# Patent

## Title
Current amplifier circuit, integrator, and ad converter

## Abstract

In one embodiment, a current amplifier circuit includes a first transistor, a first resistor, a second transistor, a second resistor, a first passive element, and a control circuit. The first transistor has a first terminal, a second terminal, and a control terminal. The first resistor has one end connected to the first terminal of the first transistor. The second transistor has a first terminal, a second terminal, and a control terminal. The second resistor has one end connected to the first terminal of the second transistor. The first passive element is connected between the first terminals of the first transistor and the second transistor. The control circuit controls at least one of voltage at the control terminals of the first transistor and the second transistor such that the voltage at the other end of the first resistor becomes equal to the voltage at the other end of the second resistor.

## Background
CROSS REFERENCE TO RELATED APPLICATION(S)
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2013-235298, filed on Nov. 13, 2013, and prior Japanese Patent Application No. 2014-215707, filed on Oct. 22, 2014, the entire contents all of which are incorporated herein by reference.
FIELD
Embodiments described herein relate generally to a current amplifier circuit, integrator, and AD converter.
BACKGROUND
In the related art, there are cases in which a sensor that detects a state of an object by changing a resistance value has a small change rate of the resistance value, such as one percent, corresponding to a state change. In the case of using such a sensor, a change of resistance value is converted to an electrical signal and then the electrical signal is amplified by an amplifier circuit. In the case where the change of the resistance value is converted to current, a current amplifier circuit is used. However, the current amplifier circuit in the related art, there is a problem in which most of bias current is consumed.
For example, it is known that a current mirror circuit is used as the current amplifier circuit in the related art. In the case of using this kind of current amplifier circuit, the change of the resistance value is converted to the current at first. Provided that the change rate of the resistance value is ΔR and the bias current is Ib, the converted current becomes: Ib (1+ΔR). In other words, the change of the resistance value is converted to the current in which signal current IbΔR is superimposed on the bias current Ib.
The converted current is received in the current mirror circuit and amplified by a multiple of a device size ratio. Here, when the device size ratio is K, the current amplified by the current mirror circuit is KIb(1+ΔR). In this case, a ratio between the bias current consumed in an entire circuit and signal current to be output (hereinafter referred to as “ratio between the bias current and the signal current”) is: KIbΔR/(Ib+KIb)=KΔR/(1+K). Since normally K is a value of one or larger, the ratio between the bias current and the signal current KΔR/(1+K) becomes ΔR or less. Thus, the signal current becomes K-fold, but the bias current is also increased, thereby not improving the ratio between the bias current and the signal current.
As a method of improving the above situation, there is a proposed method in which the ratio between the bias current and the signal current is improved by subtracting predetermined current Ib1 from the converted current Ib(1+ΔR) before being received in the current mirror circuit. According to such a current amplifier circuit, output of the current mirror circuit becomes: K (Ib−Ib1+IbΔR). Therefore, the ratio between the bias current and the signal current becomes: KIbΔR/{Ib+K (Ib−Ib1)}.
For example, in the case where Ib=200 μA, ΔR=0.01 (=1%), Ib1=197.8 μA, and K=80, total bias current becomes 376 μA (=200 μA+80×(200 μA−197.8 μA)), and the signal current becomes 160 μA (=80×200 μA×0.01). Therefore, the ratio between the bias current and the signal current is: 160/376=0.43.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating a current amplifier circuit according to a first embodiment;
FIGS. 2 to 17 are diagrams illustrating respective working examples according to the first embodiment;
FIG. 18 is a diagram of a current amplifier circuit according to a second embodiment;
FIG. 19 is a diagram illustrating an example of a passive element in FIG. 18;
FIG. 20 is a diagram illustrating another example of the passive element in FIG. 18;
FIG. 21 is a diagram illustrating a current amplifier circuit according to a third embodiment;
FIG. 22 is a diagram illustrating a current amplifier circuit according to a fourth embodiment;
FIG. 23 is a diagram of a current amplifier circuit according to a fifth embodiment;
FIGS. 24A to 24F are explanatory diagrams illustrating signal changes caused by operation of a switching circuit;
FIG. 25 is a diagram illustrating a first working example according to the fifth embodiment;
FIG. 26 is a diagram of a current amplifier circuit according to a sixth embodiment;
FIG. 27 is a diagram illustrating a first working example according to the sixth embodiment;
FIG. 28 is a diagram of a current amplifier circuit according to a seventh embodiment;
FIG. 29 is a diagram illustrating a first working example according to the seventh embodiment;
FIG. 30 is a diagram illustrating a second working example according to the seventh embodiment;
FIG. 31 is a diagram of a current amplifier circuit according to an eighth embodiment;
FIG. 32 is a diagram illustrating an example of a passive element in FIG. 31;
FIG. 33 is a diagram illustrating an integrator according to a ninth embodiment;
FIGS. 34 to 39 are diagrams illustrating respective working examples according to the ninth embodiment;
FIG. 40 is a diagram illustrating an AD converter according to a tenth embodiment;
FIG. 41 is a diagram illustrating a first working example according to the tenth embodiment;
FIG. 42 is a diagram illustrating a second working example according to the tenth embodiment;
FIG. 43 is a diagram of a current amplifier circuit according to an eleventh embodiment;
FIG. 44 is a diagram illustrating respective working example according to the eleventh embodiment;
FIG. 45 is a diagram of a current amplifier circuit according to a twelfth embodiment;
FIG. 46 is a diagram illustrating respective working example according to the twelfth embodiment;
FIG. 47 is a diagram of a current amplifier circuit according to a thirteenth embodiment;
FIG. 48 is a diagram illustrating an example of a voltage-current conversion circuit in FIG. 47;
FIG. 49 is a diagram of a current amplifier circuit according to a fourteenth embodiment;
FIG. 50 is a diagram illustrating an example of a voltage-current conversion circuit in FIG. 49;
FIG. 51 is a diagram of a current amplifier circuit according to a fifteenth embodiment; and
FIGS. 52 and 53 are diagrams illustrating another example of the current amplifier circuit in FIG. 51.



DETAILED DESCRIPTION
Embodiments will now be explained with reference to the accompanying drawings. The present invention is not limited to the embodiments.
In one embodiment, a current amplifier circuit includes a first transistor, a first resistor, a second transistor, a second resistor, a first passive element, and a control circuit. The first transistor has a first terminal, a second terminal, and a control terminal. The first resistor has one end connected to the first terminal of the first transistor. The second transistor has a first terminal, a second terminal, and a control terminal. The second resistor has one end connected to the first terminal of the second transistor. The first passive element is connected between the first terminal of the first transistor and the first terminal of the second transistor. The control circuit controls at least one of voltage at the control terminal of the first transistor and voltage at the control terminal of the second transistor such that the voltage at the other end of the first resistor becomes equal to the voltage at the other end of the second resistor.
The current amplifier circuit amplifies a differential signal received from input terminals T1 (first input terminal) and T2 (second input terminal), and executes output from output terminals T3 and T3. In the following, a current amplifier circuit formed of a MOS transistor will be described, but the current amplifier circuit can be also formed of a bipolar transistor. The current amplifier circuit can be formed of the bipolar transistor by substituting the MOS transistor described below with the bipolar transistor and further substituting a source terminal with an emitter terminal, a drain terminal with a collector terminal, and a gate terminal with a base terminal.
Further, in the following, an embodiment mainly using an N-channel MOS transistor will be described, but it is also possible to configure a current amplifier circuit mainly using a P-channel MOS transistor or a PNP type bipolar transistor. The current amplifier circuit mainly using the P-channel MOS transistor or the PNP type bipolar transistor can be formed by substituting the N-channel (P-channel) MOS transistor described below with the P-channel (N-channel) MOS transistor or with the PNP type (NPN type) bipolar transistor, and connecting a terminal connected to a ground (power source) to the power source (ground).
(First Embodiment)
In the following, a current amplifier circuit according to a first embodiment will be described with reference to FIGS. 1 to 17. Here, FIG. 1 is a diagram illustrating the current amplifier circuit according to the first embodiment. As illustrated in FIG. 1, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, a passive element Z1, and a control circuit.
The transistor M1 (first transistor) is an N-channel MOS transistor (hereinafter referred to as “NMOS transistor”). The transistor M1 has a source terminal (first terminal) connected to the resistor R1 and the passive element Z1 at a node N3, a drain terminal (second terminal) connected to an output terminal T3, and a gate terminal (control terminal) connected to the control circuit. The voltage at the gate terminal of the transistor M1 is controlled by the control circuit, and drain current IM1 flows in the transistor M1.
One end of the resistor R1 (first resistor) is connected to the source terminal of the transistor M1 and the passive element Z1 at the node N3, and the other end is connected to the control circuit at a node N1. The resistor R1 may be a fixed resistor having a constant resistance value, or may also be a sensor device that detects a state of an object by change of the resistance value.
The transistor M2 (second transistor) is an NMOS transistor. The transistor M2 has a source terminal (first terminal) connected to the resistor R2 and the passive element Z1 at a node N4, a drain terminal (second terminal) connected to an output terminal T4, and a gate terminal (control terminal) connected to the control circuit. The voltage at the gate terminal of the transistor M2 is controlled by the control circuit, and drain current IM2 flows in the transistor M2.
One end of the resistor R2 (second resistor) is connected to a source terminal of the transistor M2 and the passive element Z1 at the node N4, and the other end is connected to the control circuit at a node N2. The resistor R2 may be a fixed resistor having a constant resistance value, or may also be a sensor device that detects a state of an object by change of the resistance value. Meanwhile, in the case where the resistor R1 has the fixed resistor, preferably the resistor R2 has the fixed resistor having a resistance value equal to the resistance value of the resistor R1 (R1=R2). Additionally, in the case where the resistor R1 is the sensor device, preferably the resistor R2 is the sensor device having a same absolute value with an opposite sign of a change rate of the resistance value of the resistor R1 as next: (R1=RC(1−ΔR), and R2=RC(1+ΔR)).
The passive element Z1 (first passive element) is connected to the source terminal of the transistor M1 and one end of the resistor R1 at the node N3, and further connected to the source terminal of the transistor M2 and one end of the resistor R2 at the node N4. The passive element Z1 may be formed of resistor or capacitor. For example, the passive element Z1 may be formed of resistor and capacitor connected in series. In this case, when a frequency of an input signal is low, impedance element Z1 of the passive element Z1 is substantially determined by a capacitance component, and when the frequency is high, the impedance element Z1 is substantially determined by a resistance component. Thus, the impedance element Z1 may include frequency characteristic.
The control circuit is connected to the gate terminal of the transistor M1, the gate terminal of the transistor M2, the other end of the resistor R1, the other end of the resistor R2, and the input terminals T1 and T2. The control circuit controls at least one of the voltage at the gate terminal of the transistor M1 and the voltage at the gate terminal of the transistor M2 such that voltage V1 (first predetermined voltage) at the other end of the resistor R1 becomes equal to voltage V2 (second predetermined voltage) at the other end of the resistor R2, more specifically, the voltage V1 at the node N1 becomes equal to the voltage V2 at the node N2. Further, the control circuit executes control such that current I1 received from the input terminal T1 is applied to the resistor R1 and current I2 received from input terminal T2 is applied to the resistor R2.
Next, operation of the current amplifier circuit according to the present embodiment will be described. In the following description, note that the resistor R1 and the resistor R2 are the fixed resistor: R1=R2=RC, and the passive element Z1 is resistor. Further, the voltage V1 and voltage V2 at the nodes N1 and N2 are controlled to be VC by the control circuit (V1=V2=VC). Additionally, the current I1 and the current I2 are differential signals which are: I1=Ib(1+ΔR), and I2=Ib(1−ΔR). In other words, a description will be given for a case in which the current amplifier circuit is connected to the sensor device, and signal current is differentially received from the terminals T1 and T2.
When the current I1 and current I2 are received from the input terminals T1 and T2, voltage V3 at the node N3 and voltage V4 at the node N4 become: V3=V1+R1I1 and V4=V2+R2I2. Here, in the case of plugging following values (R1=R2=RC, I1=Ib(1+ΔR), I2=Ib(1−ΔR), and V1=V2=VC) into the mentioned formula, the voltage V3 and V4 become: V3=VC+RCIb+RCIbΔR and V4=VC+RCIb−RCIbΔR.
Accordingly, the voltage of V3−V4=2RCIbΔR is applied to the passive element Z1, and following current IZ1 flows: IZ1=2RCIbΔR/Z1. Due to this, the current IM1 flowing in the transistor M1 becomes: IM1=I1+IZ1=Ib+ΔRIb+2RCIbΔR/Z1. The current IM2 flowing in the transistor M2 becomes: IM2=I2−IZ1=Ib−ΔRIb−2RCIbΔR/Z1. According to the present embodiment, the current IM1 and current IM2 are the output signals to be output from the output terminals T3 and T4.
Here, note that bias current IB flowing in the entire circuit is a sum of bias current contained in the output signals (current IM1 and IM2), and therefore the bias current IB becomes: IB=2Ib. This is equal to a sum of the bias current contained in the input signals (current I1 and I2). In other words, according to the present embodiment, the bias current contained in the input signal is not amplified.
On the other hand, signal current ISIG output from the current amplifier circuit is a difference between the two output signals (current IM3 and IM4), and therefore the signal current becomes: ISIG=IM1−IM2=2ΔRIb+4RCIbΔR/Z1.
For example, in the case of RC=4 kΩ, ΔR=0.01, Ib=100 μA, and Z1=100Ω, the signal current contained in the input signal becomes: I1−I2=2IbΔR=2 μA. The signal current ISIG contained in the output signal becomes: ISIG=162 μA. In other words, the signal current is amplified 81-fold. Further, the bias current IB consumed in the current amplifier circuit becomes: IB=200 μA, and the ratio between the bias current and the signal current becomes 0.81. Thus, the ratio between the bias current and the signal current in the current amplifier circuit according to the present embodiment becomes larger than the ratio between the bias current and the signal current in the current amplifier circuit according to the related art.
As described above, in the current amplifier circuit according to the present embodiment, the voltage (V3−V4) corresponding to the signal current contained in the input signal is applied to the passive element Z1, thereby allowing the current IZ1 corresponding to the signal current to flow in the passive element Z1. The signal current is amplified and amplification of the bias current can be suppressed by adding the current IZ1 to the input signals (I1, I2) and generating the output signals. In this manner, the ratio between the bias current and the signal current can be improved and power consumption in the current amplifier circuit can be suppressed, compared to the current amplifier circuit in the related art.
Meanwhile, in the current amplifier circuit, only the bias current may be received from one of the input terminals T1 and T2. For example, the input signals may be: I1=Ib(1+ΔR) and I2=Ib. In this case, the signal current to be received is: I1−I2=IbΔR=1 μA. The signal current to be output is: ISIG=ΔRIb)+2RCIbΔR/Z1=81 μA. In other words, an amplification factor of the signal current is same as the case where both input signals contain the signal current. In this case, the bias current in the entire current amplifier circuit is: IB=2Ib=200 μA. Therefore, the ratio between the bias current and the signal current becomes 0.405.
(First Working Example)
FIG. 2 is a diagram illustrating a first working example according to the present embodiment. In the present working example, the current amplifier circuit includes an amplifier circuit A1 and an amplifier circuit A2 as the control circuits. The amplifier circuit A1 (A2) has a positive input terminal from which predetermined voltage VC is applied, and a negative input terminal connected to the other end of the resistor R1 (R2) at the node N1 (N2), and an output terminal connected to the gate terminal of the transistor M1 (M2). Further, the input signals I1 and I2 are received from current sources I1 and I2. Note that, in the following, the input terminals T1 and T2 correspond to the nodes N1 and N2 unless otherwise specified.
Now, operation of the control circuit according to the present working example will be described. The amplifier circuit A1 forms a feedback circuit together with the transistor M1 and the resistor R1, and executes feedback control such that voltage at the positive terminal and negative terminal in the amplifier circuit A1 become equal. More specifically, the amplifier circuit A1 controls the voltage at the gate terminal of the transistor M1 such that the voltage at the negative input terminal (voltage V1 at the node N1) becomes equal to predetermined voltage VC. In the same manner, the amplifier circuit A2 forms the feedback circuit together with the transistor M2 and the resistor R2, and executes the feedback control such that voltage at the positive terminal and negative terminal in the amplifier circuit A2 become equal. More specifically, the amplifier circuit A2 controls the voltage at the gate terminal of the transistor M2 such that the voltage at the negative input terminal (voltage V2 at the node N2) becomes equal to predetermined voltage VC. With this configuration, the voltage V1 and V2 at the nodes N1 and N2 are controlled to be equal to the voltage VC applied to the positive input terminals in the respective amplifier circuits A1 and A2.
Meanwhile, the current consumed in the operation of the amplifier circuits A1 and A2 is smaller than the bias current received in the current amplifier circuit. Therefore, in the current amplifier circuit according to the present working example, the ratio between the bias current and the signal current can be improved, compared to the current amplifier circuit in the related art.
(Second Working Example)
FIG. 3 is a diagram illustrating a second working example according to the present embodiment. According to the present working example, the resistors R1 and R2 are the sensor devices that change the resistance values in the opposite sides, centering a predetermined resistance value RC (R1=RC(1−ΔR), and R2=RC(1+ΔR)). Further, the control circuit is connected to the current sources I1 and I2 at the nodes N1 and N2, and receives the bias current (I1=Ib and I2=Ib). The configurations of other components are same as the first working example. In other words, according to the present working example, the sensor devices are disposed inside the current amplifier circuit and the input signals are generated inside the current amplifier circuit.
According to the present working example, when the current I1 and current I2 flow in the resistor R1 and R2, the voltage at the node N3 becomes: V3=VC+IbRC(1−ΔR). The voltage at the node N4 becomes: V4=VC+IbRC(1+ΔR). Therefore, the current IZ1 flowing in the passive element Z1 becomes: IZ1=−2IbRCΔR/Z1. Due to this, the current IM1 flowing in the transistor M1 becomes: IM1=Ib−2RCIbΔR/Z1. The current IM2 flowing in the transistor M2 becomes: IM2=Ib+2RCIbΔR/Z1.
With this configuration, the bias current IB in the entire current amplifier circuit becomes: IB=2Ib. And, the signal current ISIG to be output becomes: ISIG=4IbRCΔR/Z1. In other words, according to the present working example, the signal current can be amplified without amplifying the bias current in the current amplifier circuit as described above. Therefore, the ratio between the bias current and the signal current can be improved, compared to the current amplifier circuit in the related art.
Meanwhile, either the resistor R1 or R2 may be the fixed resistor having the resistance value RC. In this case, the signal current is generated at only one of the resistors R1 and R2, and the bias current IB becomes: IB=2Ib. And, the signal current ISIG becomes: ISIG=−2IbRCΔR/Z1.
(Third Working Example)
FIG. 4 is a diagram illustrating a third working example according to the present embodiment. The present working example is a modified example of the first working example, and the current amplifier circuit includes resistors R3 and R4 instead of the current sources I1 and I2 of the first embodiment. The resistor R3 and R4 are the sensor devices that change the resistance values in the opposite direction, centering the predetermined resistance value RC (R3=RC(1+ΔR), R4=RC(1−ΔR)) and the resistor R3 and R4 are respectively connected at the node N1 and N2 respectively. According to the present working example, the current I1 and I2 generated at the resistor R3 and R4 are to be the input signals.
According to the present working example, the voltage at the nodes N1 and N2 is controlled at the predetermined voltage VC, and therefore the current I1 flowing in the resistor R3 is: I1=VC/{RC(1+ΔR}, and the current I2 flowing in the resistor R4 is I2=VC/{RC(1−ΔR)}. In the case of 1>>ΔR, the current I1 and I2 can be approximated as follows: I1≦VC/RC−VCΔR/RC, I2≈VC/RC+VCΔR/RC. More specifically, the current amplifier circuit according to the present working example differentially receives, from the nodes N1 and N2, the input signal on which the signal current (VCΔR/RC) is superimposed on the bias current (VC/RC). Therefore, the current amplifier circuit according to the present working example operates in the same manner as the first working example, and the ratio between the bias current and the signal current can be improved, compared to the current amplifier circuit in the related art.
(Fourth Working Example)
FIG. 5 is a diagram illustrating a fourth working example according to the present embodiment. The current amplifier circuit according to the present working example is formed by combining the current amplifier circuit of the second working example with that of the third working example, and all of the resistors R1 to R4 are sensor devices. The resistor R1 has opposite polarity of resistance value change with respect to the resistor R2, and the resistor R3 has the opposite polarity of the resistance value change with respect to the resistor R4. More specifically, the resistors are: R1=R4=RC(1−ΔR), and R2=R3=RC(1+ΔR).
In this case, as described in the third working example, the input signal is: I1≈VC/RC−VCΔR/RC, and I2≈VC/RC+VCΔR/RC. Therefore, the voltage V3 at the node N3 can be approximated as next: V3≈VC+I1R1=2VC−2VCΔR+VC(ΔR)2≈2VC−2VCΔR. Further, the voltage V4 at the node N4 can be approximated as next: V4≈VC+I2R2=2VC+2VCΔR+VC(ΔR)2≈2VC+2VCΔR. Therefore, the current IZ1 flowing in the passive element Z1 becomes: IZ1≈4VCΔR/Z1. Here, provided that the bias current Ib=VC/RC and the signal current contained in the input signal is I1−I2=2VCΔR/RC, the bias current and the signal current become as next: IB=2Ib, and ISIG=2VCΔR/RC+8VCΔR/Z1. In other words, according to the present working example, the signal current is further amplified and amplification of the bias current is suppressed. Therefore, the ratio between the bias current and the signal current can be improved, compared to the current amplifier circuit in the related art.
(Fifth Working Example)
FIG. 6 is a diagram illustrating a fifth working example according to the present embodiment. The present working example is a concrete example of the fourth working example, in which each of the amplifier circuits A1 and A2 according to the fourth working example are formed of an amplifier circuit including a plurality of transistors.
The amplifier circuit A1 (A2) includes a transistor MA11 (MA21), a transistor MA12 (MA22), a transistor MA13 (MA23), a transistor MA14 (MA24), and a current source IbA1 (IbA2). The transistors MA11, MA12, MA21, and MA22 are NMOS transistors, and the transistors MA13, MA14, MA23, and MA24 are PMOS transistors.
The transistor MA11 (MA21) has a gate terminal from which the predetermined bias voltage VC is received, and a source terminal connected to the current source IbA1 (IbA2). The transistor MA12 (MA22) has a gate terminal connected to the node N1 (N2), and a source terminal connected to the current source IbA1 (IbA2). The transistor MA13 (MA23) and the transistor MA14 (MA24) form the current mirror circuit, and the transistor MA14 (MA24) has a drain terminal connected the gate terminal of the transistor M1 (M2).
With this configuration, when the voltage V1 (V2) at the node N1 (N2) becomes higher than the bias voltage VC, the drain current at the transistor MA11 (MA21) is decreased and the drain current is copied at the current mirror circuit. Then, the output of the amplifier circuit A1 (A2) is decreased, i.e., the voltage at the gate terminal of the transistor M1 (M2) is decreased and the voltage V1 (V2) is decreased. In the same manner, when the voltage V1 (V2) at the node N1 (N2) becomes lower than the bias voltage VC, the drain current at the transistor MA11 (MA21) is increased and the drain current is copied at the current mirror circuit. Then, the output of the amplifier circuit A1 (A2) is increased, i.e., the voltage at the gate terminal of the transistor M1 (M2) is increased and the voltage V1 (V2) is increased. Therefore, the voltage at the gate terminal of the transistor M1 (M2) is controlled by the amplifier circuit A1 (A2) such that the voltage V1 (V2) at the node N1 (N2) becomes equal to the bias voltage VC.
(Sixth Working Example)
FIG. 7 is a diagram illustrating a sixth working example according to the present embodiment. The present working example is a modified example of the fifth working example, in which the amplifier circuits A1 and A2 of the fifth working example are formed of a single amplifier circuit. In other words, according to the present working example, the control circuit is formed of the single amplifier circuit.
The control circuit includes transistors MA121, MA122, and MA123 each having a source terminal connected to the current source IbA, and transistors MA124, MA125, and MA126 forming the current mirror circuit. The transistors MA121, MA122, and MA123 are NMOS transistors, and the transistors MA124, MA125, and MA126 are PMOS transistors.
The transistor MA123 has a gate terminal from which the bias voltage VC is applied. The transistor MA121 has a gate terminal connected to the node N1, and the transistor MA122 has a gate terminal connected to the node N2. Further, transistor MA121 has a drain terminal connected to the gate terminal of the transistor M1, and the transistor MA122 has a drain terminal connected to the gate terminal of the transistor M2.
The operation of the amplifier circuit A1 according to the fifth working example is implemented by the amplifier circuit including the transistors MA121, MA123, MA124, and MA126, and the operation of the amplifier circuit A2 is implemented by the amplifier circuit including the transistors MA122, MA123, MA125, and MA126. In the control circuit according to the present working example, noise generated from the transistors MA123, MA126, and the current source IbA is superimposed on a common-mode output signal and is not superimposed on a differential output signal. Therefore, the current amplifier circuit having low noise can be achieved. Additionally, since the control circuit is configured of one single amplifier circuit, thereby achieving to reduce the current consumed at the control circuit.
(Seventh Working Example)
FIG. 8 is a diagram illustrating a seventh working example according to the present embodiment. The present working example is a modified example of the fourth working example, and further includes the transistors M3, M4 and a current source Ib—add. The transistor M3 (M4) is an NMOS transistor, having a gate terminal connected to the source terminal of the transistor M1 (M2) at a node N5 (N6), a source terminal connected to the current source Ib—add, and a drain terminal connected to the output terminal T3 (T4).
With this configuration, the voltage V3 at the node N3 is applied to the gate terminal of the transistor M3, and the voltage V4 at the node N4 is applied to the gate terminal of the transistor M4. Therefore, when the voltage V3 (V4) becomes higher than voltage V4 (V3) due to the signal current, the drain current at the transistor M3 (M4) is increased and the drain current at the transistor M4 (M3) is decreased. Due to this, the signal current can be further amplified because it is possible to generate an output signal in which the drain current of the transistor M3 (M4) having been increased (decreased) corresponding to the signal current is added to the drain current of the transistor M1 (M2).
(Eighth Working Example)
FIG. 9 is a diagram illustrating an eighth working example according to the present embodiment. The present working example is a modified example of the fifth working example, and the resistors R3 and R4 are connected to the current source I0. With this configuration, the input signals (current I1 and I2) generated at the resistor R3 and R4 can be set without depending on manufacturing variation of the resistors R3 and R4 or the bias voltage VC. For example, in the case where the current Io to be input from the current source I0 has a current value 2Ib, the current I1 and I2 become: I1=Ib(1−ΔR), and I2=Ib(1+ΔR).
(Ninth Working Example)
FIG. 10 is a diagram illustrating a ninth working example according to the present embodiment. The present working example is a modified example of the first working example, and the control circuit includes an inverting amplifier circuit A1 (A2) formed of a transistor MA11 (MA21) and a current source IbA1 (IbA2). The transistor MA11 (MA21) is an NMOS transistor, having a source terminal grounded, a gate terminal connected to the node N1 (N2), and a drain terminal connected to the current source IbA1 (IbA2) and to the gate terminal of the transistor M1 (M2).
With this configuration, the voltage at the gate terminal of the transistor M1 (M2) is controlled such that the voltage at the gate terminal of the transistor MA11 (MA21), namely, the voltage V1 (V2) at the node N1 (N2) becomes the gate-source voltage VGS—MA11 (VGS—MA21) of the transistor MA11 (MA21) determined in accordance with current at the current source IbA1 (IbA2). Therefore, the voltage V1 (V2) can be equal to the gate-source voltage VGS—MA11 (VGS—MA21) by equalizing the device size of the transistors MA11 and MA21 or the current values at the current sources IbA1 and IbA2. According to the present working example, the number of components in the control circuit can be reduced and the voltage V1 (V2) at the nodes N1 and N2 can be equalized with a more simple circuit.
(Tenth Working Example)
FIG. 11 is a diagram illustrating a tenth working example according to the present embodiment. The present working example is a modified example of the first working example, and further includes transistors M3 and M4 and output terminals T5 and T6. The transistor M3 (M4) is an NMOS transistor, having a drain terminal connected to the output terminal T5 (T6), a source terminal connected to the source terminal of the transistor M1 (M2) at the node N5 (N6), and a gate terminal connected to the control circuit. The voltage at the gate terminal of the transistor M3 (M4) is controlled by the control circuit.
With this configuration, the number of output terminals is increased and the larger number of multiple output signals can be output. A current value of the output signal output from each of the output terminals is determined by the device size ratio of each of the transistors. Note that the number of the transistors and the output terminals to be increased may be optionally selected, for example, same on the right side and left side of the passive element Z1 or may be different in each side.
(Eleventh Working Example)
FIG. 12 is a diagram illustrating an eleventh working example according to the present embodiment. The present working example is a modified example of the first working example, and includes transistors M1a (M2a) and M1b (M2b) instead of the transistor M1 (M2). The amplifier circuit A1 (A2) forming the control circuit has the negative input terminal from which the bias voltage VC1 is applied, and has the positive input terminal connected to the node N1 (N2). The transistor M1a (M2a) is a PMOS transistor, having a drain terminal connected to the resistor R1 (R2) and to the passive element Z1 at the node N3 (N4), a gate terminal connected to the control circuit, and a source terminal connected to a source terminal of the transistor M1b (M2b). The transistor M1b (M2b) is an NMOS transistor, having the source terminal connected to the source terminal of the transistor M1a (M2a), a gate terminal from which a predetermined bias voltage VC2 is applied, and a drain terminal connected to the output terminal T3 (T4).
With this configuration, when the voltage at the gate terminal of the transistor M1a (M2a) becomes high, the gate-source voltage at the transistor M1a (M2a) and transistor M1b (M2b) becomes low, thereby decreasing the current flowing in the transistor M1a (M2a) and transistor M1b (M2b). In other words, the polarity becomes opposite to the transistor M1 (M2) of the first working example. Therefore, the bias voltage VC1 is received from the negative input terminal of the amplifier circuit A1 (A2) and the positive input terminal is connected to the node N1 (N2), thereby forming a feedback circuit and achieving to control the voltage V1 (V2) at the node N1 (N2) to be the bias voltage VC1.
Further, according to the first working example, a gain from the gate terminal to the source terminal in the transistor M1 (M2) is substantially one; however, the gain from the gate terminal to the drain terminal in the transistor M1a (M2a) can be set at one or larger according to the present working example. Due to this, it is possible to make an open loop gain large and make a voltage difference between the positive input terminal and the negative input terminal of the amplifier circuit A1 (A2) small. Therefore, the control circuit according to the present working example is capable of accurately controlling the voltage at the gate terminal of the transistor M1a (M2a).
(Twelfth Working Example)
FIG. 13 is a diagram illustrating a twelfth working example according to the present embodiment. The present working example is a modified example of the eleventh working example, and further includes level shift circuits LS1 and LS2. The level shift circuit LS1 (LS2) is connected to the control circuit, the gate terminal of the transistor M1a (M2a) and the gate terminal of the transistor M2b (M1b). The level shift circuit LS1 (LS2) converts the output voltage of the amplifier circuit A1 (A2) so as to match an operating point of the transistor M2b (M1b), and applies the converted voltage to the gate terminal of the transistor M2b (M1b).
With this configuration, when the output voltage of the amplifier circuit A1 (A2), namely, the voltage at the gate terminal of the transistor M1a (M2a) becomes high, operation is executed such that the voltage at the gate terminal of the transistor M1b (M2b) becomes low. Due to this, the drain current at the transistor M1a (M2b) is further decreased, compared to the twelfth working example. Therefore, it is possible to make the gain from the gate terminal to the drain terminal at the transistor M1a (M2a) large and make the voltage difference between the positive input terminal and the negative input terminal at the amplifier circuit A1 (A2) small. As a result, the voltage at the gate terminal of the transistor M1a (M2a) can be accurately controlled.
(Thirteenth Working Example)
FIG. 14 is a diagram illustrating a thirteenth working example according to the present embodiment. The present working example is a concrete example of the twelfth working example, in which the level shift circuits LS1 and LS2 are formed of a plurality of the transistors inside the control circuit. The configuration of the control circuit is same as the eighth working example.
The level shift circuit LS1 (LS2) includes a transistor MLS11 (MLS21) and a transistor MLS12 (MLS22). The transistor MLS11 (MLS21) is a PMOS transistor, having a drain terminal connected to the gate terminal of the transistor M1a (M2a) and to the drain terminal of the transistor MA11 (MA21), a gate terminal diode-connected to the drain terminal, and a source terminal connected to a source terminal of the transistor MLS12 (MLS22). The transistor MLS12 (MLS22) is an NMOS transistor, having the source terminal connected to the source terminal of the transistor MLS11 (MLS21), a drain terminal connected to the gate terminal of the transistor M2b (M1b) and to the drain terminal of the transistor MA13 (MA23), and a gate terminal diode-connected to the drain terminal. Thus, the bias current between the level shift circuit LS1 (LS2) and the amplifier circuit A1 (A2) can be shared by disposing the level shift circuit LS1 (LS2) inside the control circuit (amplifier circuits A1 and A2). Therefore, increase of the bias current in the entire current amplifier circuit can be suppressed.
(Fourteenth Working Example)
FIG. 15 is a diagram illustrating a fourteenth working example according to the present embodiment. The present working example is a modified example of the fourth working example, in which the control circuit is formed of a single amplifier circuit A1. The amplifier circuit A1 has the negative input terminal connected to the resistor R1 at the node N1, and the positive input terminal connected to the resistor R2 at the node N2. Further, the transistor M2 has the gate terminal from which the bias voltage VC is applied. The amplifier circuit A1 compares the voltage V1 at the node N1 with the voltage V2 at the node N2, and controls the voltage at the gate terminal of the transistor M1 such that the voltage V1 and V2 become equal to a predetermined voltage set by the bias voltage VC. With this configuration, the number of components in the control circuit can be reduced.
(Fifteenth Working Example)
FIG. 16 is a diagram illustrating a fifteenth working example of the present embodiment. The present working example is a modified example of the eleventh working example, in which the control circuit is formed of the single amplifier circuit A1, same as the fourteenth working example. In this case, the polarity of the transistor M1a is opposite to the polarity of the transistor M1 of the fourteenth working example. Therefore, the amplifier circuit A1 has the positive input terminal connected to the resistor R1 at the node N1, and the negative input terminal connected to the resistor R2 at the node N2. With this configuration, the number of components in the control circuit can be reduced.
(Sixteenth Working Example)
FIG. 17 is a diagram illustrating a sixteenth working example of the present embodiment. The present working example is a modified example of the eleventh working example, in which the control circuit is formed of a common-gate circuit including transistors M5 and M6. The transistor M5 (M6) is a PMOS transistor, having a gate terminal from which the bias voltage VC1 is applied, a source terminal connected to the resistor R1 (R2) at the node N1 (N2), and a drain terminal connected to the gate terminal of the transistor M1a (M2a) and the current sources I1 and I2.
With this configuration, the input signals received from the current sources I1 and I2 are applied to the resistors R1 and R2 via the transistors M5 and M6. Further, the voltage at the source terminals of the transistors M5 and M6, namely, the voltage V1 and V2 at the nodes N1 and N2 become substantially equal in the case of ΔR<<1, because the respective current are: I1=Ib(1+ΔR) and I2=Ib(1−ΔR). With this configuration, the amplifier circuit is not used as the control circuit, and therefore increase of the bias current can be suppressed.
(Second Embodiment)
Next, a current amplifier circuit according to a second embodiment will be described with reference to FIGS. 18 to 20. Here, FIG. 18 is a diagram illustrating the current amplifier circuit according to the second embodiment. As illustrated in FIG. 18, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, a passive element Z1, and a control circuit, and impedance element Z1 of the passive element Z1 is controlled by the control signal Cont. The configurations of other components are same as the first embodiment.
The passive element Z1 according to the present embodiment may be formed of, for example, a plurality of resistors Rg1 to Rg3 connected in parallel and switches connected to the respective resistors in series, as illustrated in FIG. 19. The impedance element Z1 (resistance value in this case) can be changed by controlling opening and closing of the respective switches by the control signal Cont. Additionally, there are other possible configurations in which a plurality of capacitor is connected in parallel instead of the resistors or the resistor and the capacitor are combined.
Also, as illustrated in FIG. 20, the passive element Z1 may be configured by connecting a transistor MR and a resistor Rg in parallel. By controlling voltage at a gate terminal of the transistor MR with the control signal Cont, the passive element Z1 can be variable resistor and the impedance element Z1 can be controlled.
As described in the first embodiment, a signal current ISIG is determined by the impedance element Z1. Therefore, in the current amplifier circuit according to the present embodiment, an amplification factor of the signal current can be controlled by controlling the impedance element Z1 of the passive element Z1 by the control signal Cont.
(Third Embodiment)
Next, a current amplifier circuit according to a third embodiment will be described with reference to FIG. 21. Here, FIG. 21 is a diagram illustrating the current amplifier circuit according to the third embodiment. As illustrated in FIG. 21, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, a passive element Z1, and a control circuit. The configurations of the above components are same as the first embodiment. The current amplifier circuit according to the present embodiment further includes a transistor M3, a transistor M4, a passive element Z2, and current sources I3, I4.
The transistor M3 (third transistor) is a PMOS transistor, having a drain terminal (first terminal) connected to a drain terminal of the transistor M1 and to an output terminal T3, a gate terminal (control terminal) connected to a gate terminal of the transistor M1 and to a control circuit, and a source terminal connected to the passive element Z2 and to the current source I3.
The transistor M4 (fourth transistor) is the PMOS transistor, having a drain terminal (first terminal) connected to a drain terminal of the transistor M2 and to an output terminal T4, a gate terminal (control terminal) connected to a gate terminal of the transistor M2 and to the control circuit, and a source terminal connected to the passive element Z2 and to the current source I4.
The passive element Z2 (second passive element) is connected to a source terminal of the transistor M3 and a source terminal of the transistor M4. In the passive element Z2, current IZ2 flows. Note that the configuration of the passive element Z2 is same as the passive element Z1.
The current source I3 is connected between the source terminal of the transistor M3 and a power source and supplies bias current Ib to the transistor M3. The current source I4 is connected between the source terminal of the transistor M4 and the power source, and supplies the bias current Ib to the transistor M4.
Next, operation of the current amplifier circuit according to the present embodiment will be described. When current I1 (I2) received from an input terminal T1 (T2) becomes larger, the control circuit controls the voltage at the gate terminal of the transistor M1 (M2) such that drain current IM1 (IM2) at the transistor M1 (M2) becomes large. As a result, the voltage at the gate terminal of the transistor M1 (M2) becomes high. In this instance, voltage at the gate terminal of the transistor M3 (M4) also becomes high because the gate terminal of the transistor M3 (M4) is connected to the control circuit. Since the transistor M3 (M4) is the PMOS transistor, the drain current IM3 (IM4) becomes small when the voltage at the gate terminal becomes high.
In the same manner, when the current I1 (I2) received from the input terminal T1 (T2) becomes small, the control circuit controls the voltage at the gate terminal of the transistor M1 (M2) such that drain current IM1 (IM2) flowing in the transistor M1 (M2) becomes small. Therefore, the voltage at the gate terminal of the transistor M1 (M2) becomes low. Due to this, the voltage at the gate terminal of the transistor M3 (M4) also becomes low and the drain current IM3 (IM4) becomes large. Thus, the transistor M3 (M4) complementarily operates with respect to the transistor M1 (M2).
Therefore, when the current I1 and I2 are received from the input terminals T1 and T2, a difference between the current I1 and current I2, namely, the current IZ2 corresponding to ΔR flows in the passive element Z2, and the drain current in the transistors M3 and M4 become: IM3=Ib+IZ2, and IM4=Ib−IZ2. Due to this, the signal current ISIG contained in the output signal output from the output terminals T3 and T4 becomes a sum of IM1−IM2 and IM3−IM4.
As described above, in the current amplifier circuit according to the present embodiment, the signal current can be amplified larger than in the current amplifier circuit according to the first embodiment. Therefore, compared to the current amplifier circuit in the related art, the ratio between the bias current and the signal current can be improved.
(Fourth Embodiment)
Next, a current amplifier circuit according to a fourth embodiment will be described with reference to FIG. 22. Here, FIG. 22 is a diagram illustrating the current amplifier circuit according to the fourth embodiment. As illustrated in FIG. 22, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, a passive element Z1, a control circuit, a transistor M3, a transistor M4, a passive element Z2, and current sources I3 and I4. According to the present embodiment, a gate terminal of the transistor M3 (M4) is connected to a source terminal of the transistor M1 (M2), and the configurations of other components are same as the third embodiment.
Next, operation of the current amplifier circuit according to the present embodiment will be described. Voltage V1 (V2) at a node N1 (N2) is controlled to be same by the control circuit, and therefore, when current I1 (I2) received from an input terminal T1 (T2) becomes larger, voltage V3 (V4) at a node N3 (N4) becomes large. A gate terminal of the transistor M3 (M4) is connected to a source terminal of the transistor M1 (M2), namely, the node N3 (N4), and therefore the voltage at the gate terminal of the transistor M3 (M4) becomes high. Since the transistor M3 (M4) is a PMOS transistor, drain current IM3 (IM4) becomes small when the voltage at the gate terminal becomes high.
In the same manner, when the current I1 (I2) received from the input terminal T1 (T2) becomes small, the voltage V3 (V4) at the node N3 (N4) becomes low, and also the voltage at the gate terminal of the transistor M3 (M4) becomes low and the drain current IM3 (IM4) becomes large. Thus, the transistor M3 (M4) complementarily operates with respect to the transistor M1 (M2). Therefore, in the current amplifier circuit according to the present embodiment, signal current ISIG contained in an output signal output from the output terminals T3 and T4 is a sum of IM1−IM2 and IM3−IM4, and signal current can be amplified larger than the current amplifier circuit according to the first embodiment, same as the third embodiment. Meanwhile, according to the present embodiment, in the case where the current I1 and I2 are small and the transistors M3 and M4 operate in a saturation region, the current IM3 and IM4 change in accordance with ΔR. Therefore, the source terminals of the transistors M3 and M4 may be short-circuited (Z2=0).
(Fifth Embodiment)
Next, a current amplifier circuit according to a fifth embodiment will be described with reference to FIGS. 23 to 25. Here, FIG. 23 is a diagram illustrating the current amplifier circuit according to the fifth embodiment. As illustrated in FIG. 23, the present embodiment is a modified example of the first embodiment, and includes a switching circuit whereby paths are switched such that current IM1 flowing in a transistor M1 and current IM2 flowing in a transistor M2 are alternately switched. The switching circuit includes a switch 1 and a switch 2.
The switch 1 (first switch) is a chopper circuit that switches a path between a path of the current IM1 output from a drain terminal of the transistor M1 and a path of the current IM2 output from a drain terminal of the transistor M2. The switch 1 is disposed between output terminals T3, T4 of the current amplifier circuit and input terminals T5, T6 of a post-stage circuit where output signals are received from the current amplifier circuit. The switch 1 alternately switches the path between the path in which the output terminal T3 and the input terminal T5 are connected and also the output terminal T4 and the input terminal T6 are connected, and the path in which the output terminal T3 and the input terminal T6 are connected and also the output terminal T4 and input terminal T5 are connected.
In the case where the output terminal T3 and the input terminal T5 are connected and the output terminal T4 and the input terminal T6 are connected by the switch 1, the current IM1 output from the output terminal T3 is received in the input terminal T5 and the current IM2 output from the output terminal T4 is received in the input terminal T6. When the switch 1 switches the path, the output terminal T3 is connected to the input terminal T6 and the output terminal T4 is connected to the input terminal T5. Due to this, the current IM1 output from the output terminal T3 is received in the input terminal T6, and the current IM2 output from the output terminal T4 is received in the input terminal T5.
The switch 2 (second switch) is a chopper circuit that switches the path between a path of current I1 received from the other end of a resistor R1, namely, a node N1, and a path of current I2 received from the other end of a resistor R2, namely, a node N2. The switch 2 is disposed between the input terminals T1, T2 and the nodes N1, N2 in the current amplifier circuit. The switch 2 alternately switches the path between the path in which the input terminal T1 and the node N1 are connected and also the input terminal T2 and the node N2 are connected, and the path in which the input terminal T1 and the node N2 are connected and also the input terminal T2 and the node N1 are connected.
In the case where the input terminal T1 and the node N1 are connected and the input terminal T2 and the node N2 are connected by the switch 2, the current I1 received from the input terminal T1 is received at the node N1 via a control circuit and the current I2 received from the input terminal T2 is received at the node N2 via the control circuit. When the switch 2 switches the path, the input terminal T1 is connected to the node N2 and the input terminal T2 is connected to the node N1. Due to this, the current I1 received from the input terminal T1 is received at the node N2 via the control circuit, and the current I2 received from the input terminal T2 is received at the node N1 via the control circuit.
Switching timings of the switch 1 and the switch 2 are synchronized. The switches 1 and 2 operate such that the switch 2 connects the input terminal T1 (T2) to the node N1 (N2) in the case where the switch 1 connects the output terminal T3 (T4) to the input terminal T5 (T6), and the switch 2 connects the input terminal T1 (T2) to the node N2 (N1) in the case where the switch 1 connects the output terminal T3 (T4) to the input terminal T6 (T5).
FIGS. 24A to 24F are diagrams for describing changes of a signal by the operation of the switching circuit. In the following, a description will be given for the case in which a signal component exists in a low-frequency region of an input signal as illustrated in FIG. 24A. The current amplifier circuit sometimes generates noise in the process of amplifying the input signal. Particularly, flicker noise (1/f noise) may be generated in the low-frequency region as illustrated in FIG. 24B. In the case where such noise is generated, the output signal of the current amplifier circuit becomes a signal in which a signal component and a noise component are superimposed in the low-frequency region, as illustrated in FIG. 24C.
On the other hand, in the case where the signal is amplified while the switching circuit switches the path at a predetermined frequency, the signal component contained in the input signal is shifted to a high-frequency region by an amount of frequency switched by the switch 2 as illustrated in FIG. 24D. The output signal becomes a signal in which the signal component shifted to the high-frequency region and the noise component in the above-mentioned low-frequency region are superimposed. Therefore, as illustrated in FIG. 24E, the signal component contained in the output signal and the noise component are not overlapped.
In the output signal, switching frequency is combined again by the switch 1. Here, in the case of setting phases of the switching frequency of the switch 1 and switch 2 inversed, the signal component contained in the output signal is returned to the low-frequency region, and the noise component is shifted to the high-frequency region, as illustrated in FIG. 24F. Therefore, in the current amplifier circuit according to the present embodiment, the noise component can be easily removed from the output signal by a filter such as a lowpass filter. With this configuration, influence of the noise generated in the current amplifier circuit can be suppressed.
(First Working Example)
FIG. 25 is a first working example of the present embodiment. The present working example is a concrete example of the fifth embodiment, where the switching circuit is applied in the current amplifier circuit of the first working example according to the first embodiment. With this configuration, the noise generated at the current amplifier circuit can be easily removed from the output signal.
(Sixth Embodiment)
Next, a current amplifier circuit according to a sixth embodiment will be described with reference to FIGS. 26 and 27. Here, FIG. 26 is a diagram illustrating the current amplifier circuit according to the sixth embodiment. As illustrated in FIG. 26, the present embodiment is a modified example of the fifth embodiment, and includes a switching circuit whereby paths are switched such that current IM1 flowing in a transistor M1 and current IM2 flowing in a transistor M2 are alternately switched. In the description of the present embodiment, a control circuit portion for controlling voltage at a gate terminal of the transistor M1 is referred to as control circuit 1, and a control circuit portion for controlling voltage at a gate terminal of the transistor M2 is referred to as control circuit 2. The configurations of other components are same as the first embodiment. The switching circuit includes a switch 1, a switch 3, a switch 4, and a switch 5. Note that description for the configuration of the switch 1 will be omitted here as is same as the fifth embodiment.
The switch 3 (third switch) is a chopper circuit that switches a path between one end of a resistor R1, namely, a path of current I1 output from the side of a node N3 of the resistor R1, and one end of a resistor R2, namely, a path of current I2 output from the side of a node N4 of the resistor R2. The switch 3 is disposed between the resistors R1, R2 and the nodes N3, N4. The switch 3 alternately switches the path between the path in which the resistor R1 and the node N3 are connected and also the resistor R2 and the node N4 are connected, and the path in which the resistor R1 and the node N4 are connected and also the resistor R2 and the node N3 are connected.
In the case where the resistor R1 and the node N3 are connected and the resistor R2 and the node N4 are connected by the switch 3, the current I1 output from one end of the resistor R1 is received at the node N3 and the current I2 output from one end of the resistor R2 is received at the node N4. When the switch 3 switches the path, the resistor R1 is connected to the node N4 and the resistor R2 is connected to the node N3. Due to this, the current I1 output from one end of the resistor R1 is received at the node N4, and the current I2 output from one end of the resistor R2 is received at the node N3.
The switch 4 (fourth switch) is a chopper circuit that switches the path for the current I1 and I2 received in the control circuit 1 in order to control the voltage at the gate terminal of the transistor M1. The switch 4 is disposed between the input terminals T1, T2 and the control circuit 1. The switch 4 alternatively switches the path between the path in which the input terminal T1 and the control circuit 1 are connected, and the path in which the input terminal T2 and the control circuit 1 are connected.
In the case where the input terminal T1 and the control circuit 1 are connected by the switch 4, the voltage at the input terminal T1, namely the voltage at the other end of the resistor R1 is received in the control circuit 1. When the switch 4 switches the path, the input terminal T2 is connected to the control circuit 1 and the voltage at the input terminal T2, namely the voltage at the other end of the resistor R2 is received in the control circuit 1.
The switch 5 (fifth switch) is a chopper circuit that switches the path for the current I1 and I2 received in the control circuit 2 in order to control the voltage at the gate terminal of the transistor M2. The switch 5 is disposed between the input terminals T1, T2 and the control circuit 2. The switch 5 alternatively switches the path between the path in which the input terminal T1 and the control circuit 2 are connected, and the path in which the input terminal T2 and the control circuit 2 are connected.
In the case where the input terminal T1 and the control circuit 2 are connected by the switch 5, the voltage at the input terminal T1, namely, the voltage at the other end of the resistor R1 is received in the control circuit 2. When the switch 5 switches the path, the input terminal T2 is connected to the control circuit 2 and the voltage at the input terminal T2, namely, the voltage at the other end of the resistor R2 is received in the control circuit 2.
Switching timings of the switches 1, 3, 4 and 5 are synchronized. In the case where the switch 1 connects an output terminal T3 (T4) to an input terminal T5 (T6), the switch 3 connects the resistor R1 (R2) to the node N3 (N4), the switch 4 connects the input terminal T1 to the control circuit 1, and the switch 5 connects the input terminal T2 to the control circuit 2. In this case, signal current of the current I1 (I2) received from the input terminal T1 (T2) is amplified and received in the input terminal T5 (T6). The control circuit 1 (control circuit 2) forms a negative feedback circuit together with the transistor M1 (M2) and the resistor R1 (R2), and controls the voltage at the gate terminal of the transistor M1 (M2) such that voltage at a node N1 (N2) becomes a predetermined voltage.
On the other hand, in the case where the switch 1 connects an output terminal T3 (T4) to an input terminal T6 (T5), the switch 3 connects the resistor R1 (R2) to the node N4 (N3), the switch 4 connects the input terminal T2 to the control circuit 1, and the switch 5 connects the input terminal T1 to the control circuit 2. In this case, the signal current of the current I1 (I2) received from the input terminal T1 (T2) is amplified and received in the input terminal T5 (T6). The control circuit 1 (control circuit 2) forms the negative feedback circuit together with the transistor M1 (M2) and the resistor R2 (R1), and controls the voltage at the gate terminal of the transistor M1 (M2) such that voltage at a node N2 (N1) becomes the predetermined voltage.
With the above-described structure, in the current amplifier circuit according to the present embodiment, noise component can be easily removed from the output signal by a filter such as a lowpass filter in the same manner as the fifth embodiment. Due to this, influence of the noise generated in the current amplifier circuit can be suppressed.
(First Working Example)
FIG. 27 is a diagram illustrating a first working example of the present embodiment. The present working example is a concrete example of the present embodiment, where the switching circuit is applied in a fourth working example of the first embodiment. In the present working example, the control circuit 1 is an amplifier circuit A1, and the control circuit 2 is an amplifier circuit A2. With this configuration, the noise generated in the current amplifier circuit can be easily removed from the output signal.
(Seventh Embodiment)
Next, a current amplifier circuit according to a seventh embodiment will be described with reference to FIGS. 28 to 30. Here, FIG. 28 is a diagram illustrating the current amplifier circuit according to the seventh embodiment. As illustrated in FIG. 28, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a passive element Z1, and a control circuit. In other words, the current amplifier circuit according to the present embodiment is formed of a current amplifier circuit according to the above-described embodiments in a single-ended configuration.
The transistor M1 (first transistor) is an NMOS transistor having a source terminal (first terminal) connected to the resistor R1 and the passive element Z1 at a node N3, a drain terminal (second terminal) connected to an output terminal T3, and a gate terminal (control terminal) connected to the control circuit. Voltage at the gate terminal of the transistor M1 is controlled by the control circuit, and drain current IM1 flows in the transistor M1.
The resistor R1 (first resistor) has one end connected to the source terminal of the transistor M1 and to the passive element Z1 at the node N3, and the other end connected to the control circuit at a node N1. The resistor R1 may be a fixed resistor having a constant resistance value, or may be a sensor device that detects a state of an object by change of the resistance value.
The passive element Z1 (first passive element) has one end connected to the source terminal of the transistor M1 and to one end of the resistor R1 at the node N3, and the other end connected to the ground (reference potential). The passive element Z1 is formed of at least a capacitor, and an operating point of the current amplifier circuit is fixed by this capacitor. The passive element Z1 may include resistor.
The control circuit is connected to the gate terminal of the transistor M1, the other end of the resistor R1, and an input terminal T1. The control circuit controls the voltage at the gate terminal of the transistor M1 such that voltage at the other end of the resistor R1 becomes equal to a predetermined voltage (first predetermined voltage), namely, such that voltage V1 at the node N1 becomes equal to the predetermined voltage. Further, the control circuit executes control such that current I1 received from the input terminal T1 is applied to the resistor R1.
Next, operation of the current amplifier circuit according to the present embodiment will be described. In the following description, the resistor R1 is a fixed resistor: R1=RC. The voltage V1 at the node N1 is controlled by the control circuit to be a voltage value VC (V1=VC). Also, the current I1 is: I1=Ib (1+ΔR). More specifically, a description will be given for a case in which the current amplifier circuit is connected to a sensor device, and signal current is received from the input terminal T1.
When the current I1 is received from the input terminal T1, the voltage V3 at the node N3 is: V3=V1+R1I1. When following values R1=RC, I1=Ib(1+ΔR), and V1=VC are plugged into the above formula, the voltage V3 becomes: V3=VC+R1Ib+R1IbΔR.
Since the passive element Z1 is connected between the node N3 and the ground, the voltage V3 at the node N3 is applied. The passive element Z1 includes the capacitor, and therefore direct current does not flow. For this reason, following current IZ1 corresponding to an AC component of the voltage V3, namely, R1IbΔR flows in the passive element Z1, and the current IZ1 is: IZ1=R1IbΔR/Z1. Due to this, the current IM1 flowing in the transistor M1 becomes: IM1=I1+IZ1=Ib+ΔRIb, +RCIbΔR/Z1. According to the present embodiment, the current IM1 becomes an output signal output from the output terminal T3.
Therefore, bias current IB flowing in the entire circuit becomes: IB=Ib. And, signal current ISIG contained in the output signal becomes: ISIG=ΔRIb+RCIbΔR/Z1. As described above, the signal current is amplified and further amplification of the bias current can be suppressed in the current amplifier circuit according to the present embodiment, same as the above-described embodiment. Due to this, the ratio between the bias current and the signal current can be improved and power consumption in the current amplifier circuit can be suppressed, compared to the current amplifier circuit according to the related art.
(First Working Example)
FIG. 29 is a first working example of the present embodiment. According to the present working example, the current amplifier circuit includes an amplifier circuit A1 as a control circuit. The amplifier circuit A1 has a positive input terminal from which predetermined bias voltage VC is applied, a negative input terminal connected to the other end of the resistor R1 at the node N1, and an output terminal connected to the gate terminal of the transistor M1. Further, a resistor R3 is connected to the input terminal T1, and current I1R3 generated at the resistor R3 becomes an input signal. The resistors R1 and R3 are sensor devices having following resistance values that change in the opposite direction, centering a predetermined resistance value RC: R1=RC(1−ΔR) and R3=RC(1+ΔR).
In the following, operation of the control circuit (amplifier circuit A1) according to the present working example will be described. The amplifier circuit A1 forms a feedback circuit together with the transistor M1 and the resistor R1, and executes feedback control such that the voltage at the positive and negative terminals of the amplifier circuit A1 become equal. In other words, the amplifier circuit A1 controls the voltage at the gate terminal of the transistor M1 such that the voltage at the negative input terminal (voltage V1 at the node N1) becomes equal to the bias voltage VC. With this configuration, the voltage V1 at the node N1 is controlled to be equal to the bias voltage VC applied to the positive input terminal of the amplifier circuit A1.
Note that the current consumed by the operation of the amplifier circuit A1 is smaller than the bias current received in the current amplifier circuit. Therefore, the ratio between the bias current and the signal current can be improved in the current amplifier circuit according to the present working example, compared to the current amplifier circuit according to the related art.
(Second Working Example)
FIG. 30 is a second working example of the present embodiment. The present working example is a concrete example of the first working example, and formed of an amplifier circuit in which the amplifier circuit A1 of the first working example includes a plurality of transistors. Further, the passive element Z1 includes the capacitor and the resistor. The amplifier circuit A1 includes a transistor MA11, a transistor MA12, a transistor MA13, a transistor MA14, and a current source IbA1. The transistors MA11 and MA12 are NMOS transistors and the transistors MA13 and MA14 are PMOS transistors.
The transistor MA11 has a gate terminal from which the predetermined bias voltage VC is applied, and a source terminal connected to the current source IbA1. The transistor MA12 has a gate terminal connected to the node N1, and a source terminal connected to the current source IbA1. The transistor MA13 and the transistor MA14 form a current mirror circuit, and a drain terminal of the transistor MA14 is connected to the gate terminal of the transistor M1. With this configuration, the voltage at the transistor M1 is controlled by the amplifier circuit A1 such that the voltage V1 at the node N1 becomes equal to the bias voltage VC.
(Eighth Embodiment)
Next, a current amplifier circuit according to an eighth embodiment will be described with reference to FIGS. 31 and 32. Here, FIG. 31 is a diagram illustrating the current amplifier circuit according to the eighth embodiment. As illustrated in FIG. 31, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a passive element Z1, and a control circuit, and impedance element Z1 of the passive element Z1 is controlled by a control signal Cont. The configurations of other components are same as the seventh embodiment.
The passive element Z1 according to the present embodiment may include, for example, a plurality of resistors connected in parallel, switches connected to the respective resistors in series, and a single capacitor connected to the respective resistors in series, as illustrated in FIG. 32. The impedance element Z1 can be changed by controlling opening and closing of each switch with the control signal Cont. In the current amplifier circuit according to the present embodiment, an amplification factor of the signal current can be controlled by controlling the impedance element Z1 of the passive element Z1 with the control signal Cont. Meanwhile, the passive element Z1 may include a plurality of capacitor connected in series to each of the resistors. Frequency characteristics of the passive element Z1 can be optionally set by adjusting time constant of the resistor and the capacitor connected in series. For example, the frequency characteristics of the passive element Z1 can be set constant by matching the time constant before and after switching of the switch.
(Ninth Embodiment)
Next, an integrator according to a ninth embodiment will be described with reference to FIGS. 33 to 39. Here, FIG. 33 is a diagram illustrating the integrator according to the ninth embodiment. As illustrated in FIG. 33, the integrator according to the present embodiment includes a current amplifier circuit according to the above-described embodiments and an integrating element that integrates an output signal of the current amplifier circuit, and includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, a passive element Z1, and a control circuit. The configurations of the above components are same as a current amplifier circuit according to the first embodiment.
The integrator according to the present embodiment further includes a capacitor element C connected to output terminals T3 and T4. The capacitor element C is formed including at least the capacitor. The capacitor element C integrates the output signal from the output terminals T3 and T4. The integrator can be easily created by the capacitor element C because the output signal of the current amplifier circuit is current.
(First Working Example)
FIG. 34 is a first working example of the present embodiment. The present working example is a modified example of the first working example according to the first embodiment, and includes a capacitor C0 as the capacitor element C and further includes current sources I3 and I4. The capacitor C0 is connected to the output terminals T3 and T4, and integrates the output signals. Current I3 and I4 of the current sources I3 and I4 are: I3=I4=Ib. Therefore, only signal current ISIG contained in the output signal can be integrated by the capacitor CO.
(Second Working Example)
FIG. 35 is a second working example of the present embodiment. The present working example is a modified example of the first working example, and includes the capacitor C0 and a resistor RC connected to the capacitor C0 in series. With this configuration, phase compensation can be executed by inserting a zero point into the frequency characteristics. In this manner, the operation can be stabilized.
(Third Working Example)
FIG. 36 is a third working example of the present embodiment. The present working example is a modified example of the first working example, and includes capacitor C1 and C2 as the capacitor element C. The capacitor C1 (first capacitor) is connected between ground and the output terminal T3, namely, between the ground and a drain terminal of the transistor M1. The capacitor C2 (second capacitor) is connected between the ground and the output terminal T4, namely, between the ground and a drain terminal of the transistor M2. In the capacitor C1 and C2, the signal current contained in the output signal from the output terminals T3 and T4 is integrated. Meanwhile, in the case of using the integrator according to the present working example as a filter, the resistor may be connected to the capacitor C1 and C2 in series, same as the second working example. Due to this, the zero is introduced into the frequency characteristics, thereby achieving to perform the phase compensation and stabilize the operation.
(Fourth Working Example)
FIG. 37 is a fourth working example of the present embodiment. The present working example is a modified example of the third embodiment, and includes the capacitor C0 connected between the output terminals T3 and T4 as the capacitor element C. According to the present working example also, only the signal current ISIS contained in the output signal can be integrated by the capacitor CO.
(Fifth Working Example)
FIG. 38 is a fifth working example of the present embodiment. The present working example is a modified example of the fourth embodiment, and includes the capacitor C1 and C2 as the capacitor element, and further includes an amplifier circuit Ainteg. The amplifier circuit Ainteg has differential inputs and differential outputs, and has a positive input terminal connected to the output terminal T3 and a negative input terminal connected to the output terminal T4. The capacitor C1 (C2) is connected between the positive input terminal T3 (negative input terminal T4) and the negative output terminal T7 (positive output terminal T8) of the amplifier circuit Ainteg. With this configuration, the input terminals of the amplifier circuit Ainteg are virtually shorted, and the voltage between input terminals becomes equal. Therefore, even when an output voltage range of the current amplifier circuit is narrow, the output signal can be integrated.
(Sixth Working Example)
FIG. 39 is a diagram illustrating a sixth working example of the present embodiment. The present working example is a modified example of the first working example of the seventh embodiment, and includes the capacitor C1 and C2 as the capacitor element, and further includes the amplifier circuit Ainteg. The configurations of the capacitor C1, C2 and the amplifier circuit Ainteg are same as the fifth working example. With this configuration, the input terminals of the amplifier circuit Ainteg are virtually shorted, and the voltage between the input terminals of the amplifier circuit Ainteg becomes equal. Therefore, even when an output voltage range of the current amplifier circuit is narrow, the output signal can be integrated. Further, the voltage between input and output of a switch 1, namely, between the output terminals T3, T4 and the input terminals T5 and T6 becomes small, and therefore, in the case of implementing the switch 1 in a MOS transistor, it is possible to suppress distortion of a signal caused by fluctuation of ON-resistance of the switch.
(Tenth Embodiment)
Next, an AD converter according to a tenth embodiment will be described with reference to FIGS. 40 to 42. Here, FIG. 40 is a diagram illustrating the AD converter according to the tenth embodiment. As illustrated in FIG. 40, the AD converter according to the present embodiment includes the current amplifier according to the above-described embodiments, a current-voltage conversion circuit, and an AD conversion circuit ADC. In FIG. 40, the configuration of the current amplifier is same as the first embodiment.
The current-voltage conversion circuit is connected to output terminals T3 and T4 of the current amplifier circuit and the AD conversion circuit ADC. The current-voltage conversion circuit converts differential signal current (output signal) output from the current amplifier circuit to differential signal voltage, and the differential signal voltage is received in the AD conversion circuit ADC. Meanwhile, in the case where the input signal of the AD conversion circuit ADC is current, the current-voltage conversion circuit is unnecessary. In this case, for example, the output terminals T3 and T4 of the current amplifier circuit may be directly connected to the AD conversion circuit ADC.
The AD conversion circuit ADC converts the differential signal voltage received via the current-voltage conversion circuit to a digital signal. This enables a state change of an object detected by a sensor to be output as the digital signal. In the AD converter according to the present embodiment, the AD conversion circuit ADC can be optionally selected. For example, it is possible to use a pipeline AD conversion circuit, a successive-approximation type AD conversion circuit, a single slope AD conversion circuit, a discrete time ΔΣAD conversion circuit, a continuous time ΔΣAD conversion circuit, and so on.
(First Working Example)
FIG. 41 is a diagram illustrating a first working example of the AD converter according to the present embodiment. The present working example is a concrete example of the AD converter in FIG. 40, and the current-voltage converter includes current sources I3, I4 and a resistor RV. The current sources I3 and I4 apply bias current Ib, and the resistor RV is connected between the output terminals T3 and T4. The differential signal current flows in the resistor RV, thereby generating voltage at both ends of the resistor RV, and the generated voltage is received by the AD conversion circuit ADC as the differential signal voltage.
(Second Working Example)
FIG. 42 is a diagram illustrating a second working example of the AD converter according to the present embodiment. The present working example is a modified example of the first working example, and the current-voltage converter includes resistors RV1, RV2 and transistors MV1, MV2. The resistors RV1 and RV2 are connected between the output terminals T3 and T4 in series. The transistor MV1 (MV2) is a PMOS transistor, having a gate terminal mutually connected with a gate terminal of the other transistor, a source terminal connected to a power source, and a drain terminal connected to the output terminals T3 (T4). The resistors RV1 and RV2 have nodes connected to nodes of the transistors MV1 and MV2. With this configuration, the output signal of the current amplifier circuit can be converted to the voltage.
(Eleventh Embodiment)
Next, a current amplifier circuit according to an eleventh embodiment will be described with reference to FIGS. 43 and 44. Here, FIG. 43 is a diagram illustrating the current amplifier circuit according to the eleventh embodiment. As illustrated in FIG. 43, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, a passive element Z1, and a control circuit. The configurations of the above components are same as the first embodiment. The current amplifier circuit according to the present embodiment further includes a transistor MC1 and a transistor MC2.
The transistor MC1 (fifth transistor) is an NMOS transistor, having a source terminal (first terminal) connected to an input terminal T1 and a drain terminal (second terminal) connected to the control circuit and the other end of the resistor R1 at a node N1, and applied with a predetermined bias voltage Vc2 (third predetermined voltage) from a gate terminal (control terminal). In other words, the transistor MC1 forms a common-gate circuit.
The transistor MC2 (sixth transistor) is an NMOS transistor, having a source terminal (first terminal) connected to an input terminal T2 and a drain terminal (second terminal) connected to the control circuit and the other end of the resistor R2 at the node N2, and applied with the predetermined bias voltage Vc2 from a gate terminal (control terminal). In other words, the transistor Mc2 forms a common-gate circuit.
With this configuration, the current amplifier circuit according to the present embodiment can suppress influence of the noise of the control circuit onto the output signal. The reason is as follows.
In a case where the control circuit and the input terminals T1 and T2 are directly connected as illustrated in the current amplifier circuit according to the first embodiment, a noise component is superimposed on current I1 and I2 input from the input terminals T1 and T2 respectively due to the influence of the noise of the control circuit. Then, the noise component contained in the current I1 and I2 is converted by the resistors R1 and R2 respectively to the voltage, converted by the passive element Z1 to the current, and superimposed on the output signal. For this reason, for the use of low noise to be required, the control circuit for the low noise is necessary.
On the other hand, in the current amplifier circuit according to the present embodiment, the transistors Mc1 and Mc2 are respectively connected between the control circuit and the input terminals T1 and T2, the impedance when the input terminals T1 and T2 are viewed from the control circuit becomes high, the noise component contained in the current I1 and I2 can be reduced. Therefore, influence of the noise of the control circuit on the output signal can be suppressed.
(First Working Example)
FIG. 44 is a diagram illustrating a first working example of the present embodiment. The present working example is a concrete example of the present embodiment, where the transistors Mc1 and Mc2 are provided in the third working example (see FIG. 4) according to the first embodiment.
As described in the present working example, in a case where the transistor Mc1 is provided between an amplifier circuit A1 and a resistor R3, an input conversion noise Vn1 of the amplifier circuit A1 is applied to the node N1, the impedance of the input terminal T1 viewed from the amplifier circuit A1 becomes R3×gmMc1×roMc1. Here, gmMc1 is the transconductance of the transistor Mc1, and roMc1 is the output resistance of the transistor Mc1. In the case of 1<<gmMc×roMc1, the voltage (noise voltage) according to the noise component applied to the source terminal of the transistor M1 (the node N3) becomes Vn1+Vn1×R1/(R3×gmMc1×roMc1)≈Vn1.
On the other hand, as described in the third working example of the first embodiment, in a case where the amplifier circuit A1 and the resistor R3 are directly connected, the input conversion noise Vn1 of the amplifier circuit A1 is applied to the node N1, the impedance of the input terminal T1 viewed from the amplifier circuit A1 becomes R3. Therefore, the noise component of Vn1/R3 is superimposed on the current I1, and the noise component is converted into a voltage by the resistor R1. As a result, the noise voltage applied to the source terminal of the transistor M1 (the node N3) becomes Vn1+Vn1×R1/R3=Vn1(R1+R3)/R3.
Thus, the noise voltage applied to the node N3 can be reduced by disposing the transistor Mc1 compared to the case where the amplifier circuit A1 and the resistor R3 are directly connected. The same thing is applied for the transistor Mc2. Therefore, as described above, influence of the noise of the control circuit onto the output signal can be suppressed.
(Twelfth Embodiment)
Next, a current amplifier circuit according to a twelfth embodiment will be described with reference to FIGS. 45 and 46. Here, FIG. 45 is a diagram illustrating the current amplifier circuit according to the twelfth embodiment. As illustrated in FIG. 45, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a passive element Z1, and a control circuit. The configurations of the above components are same as the seventh embodiment. The current amplifier circuit according to the present embodiment further includes a transistor MC1.
The transistor MC1 (second transistor) is an NMOS transistor, having a source terminal (first terminal) connected to an input terminal T1 and a drain terminal (second terminal) connected to the control circuit and the other end of the resistor R1 at a node N1, and a predetermined bias voltage Vc2 (second predetermined voltage) is input from a gate terminal (control terminal). In other words, the transistor Mc1 forms a common-gate circuit.
With this configuration, the current amplifier circuit according to the present embodiment can suppress influence of the noise of the control circuit onto the output signal.
(First Working Example)
FIG. 46 is a diagram illustrating a first working example of the present embodiment. The present working example is a concrete example of the present embodiment, where the transistor Mc1 is provided in the first working example (see FIG. 29) of the seventh embodiment.
As described in the present working example, in a case where the transistor Mc1 is provided between an amplifier circuit A1 and a resistor R3, an input conversion noise Vn1 of the amplifier circuit A1 is applied to the node N1, the impedance of the input terminal T1 viewed from the amplifier circuit A1 becomes R3×gmMc1×roMc1. Here, gmMc1 is the transconductance of the transistor Mc1, and roMc1 is the output resistance of the transistor Mc1. In the case of 1<<gmMc1×roMc1, the voltage (noise voltage) according to the noise component applied to the source terminal of the transistor M1 (the node N3) becomes Vn1+Vn1×R1/(R3×gmMc1×roMc1)≈Vn1.
On the other hand, as described in the first working example of the seventh embodiment, in a case where the amplifier circuit A1 and the resistor R3 are directly connected, the input conversion noise Vn1 of the amplifier circuit A1 is applied to the node N1, the impedance of the input terminal T1 viewed from the amplifier circuit A1 becomes R3. Therefore, the noise component of Vn1/R3 is superimposed on the current I1, and the noise component is converted into a voltage by the resistor R1. As a result, the noise voltage applied to the source terminal of the transistor M1 (the node N3) becomes Vn1+Vn1×R1/R3=Vn1 (R1+R3)/R3.
Thus, the noise voltage applied to the node N3 can be reduced by disposing the transistor Mc1 compared to the case where the amplifier circuit A1 and the resistor R3 are directly connected. Therefore, as described above, influence of the noise of the control circuit onto the output signal can be suppressed.
(Thirteenth Embodiment)
Next, a current amplifier circuit according to a thirteenth embodiment will be described with reference to FIGS. 47 and 48. Here, FIG. 47 is a diagram illustrating the current amplifier circuit according to the thirteenth embodiment. As illustrated in FIG. 47, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, and a control circuit. The configurations of the above components are same as the first embodiment. In the present embodiment, the configuration of the passive element Z1 is different from the first embodiment. In addition, a voltage-current conversion circuit Gm is connected to the passive element Z1.
The passive element Z1 includes a resistor RZ11 (third resistor), a capacitor CZ1, and a resistor RZ12 (fourth resistor). One end of the resistor RZ11 is connected to one end of the resistor R1 and the source terminal of the transistor M1 at the node N3, and the other end is connected to one end of the capacitor CZ1. One end of the resistor RZ12 is connected to one end of the resistor R2 and the source terminal of the transistor M2 at the node N4, and the other end is connected to the other end of the capacitor CZ1. In other words, the resistor RZ11, the capacitor CZ1, and the resistor RZ12 are connected in series.
The voltage-current conversion circuit Gm includes two input terminals InP (first input terminal) and InM (second input terminal) and two output terminals OutP (first output terminal) and OutM (second output terminal). The voltage-current conversion circuit Gm converts voltages input from the input terminals InP and InM into currents by a predetermined voltage-current conversion coefficient Gm, and outputs the converted currents to the output terminals OutP and OutM, respectively.
The input terminal InP of the voltage-current conversion circuit Gm is connected to the other end of the resistor RZ11, the output terminal OutP is connected to one end of the resistor RZ11, the input terminal InM is connected to the other end of the resistor RZ12, and the output terminal OutM is connected to one end of the resistor RZ12.
In the present embodiment, a voltage V3 at the node N3 becomes V3=V1+R1I1, and a voltage V4 at the node N4 becomes V4=V2+R2I2. Here, for example, in the case where R1=R2=RC, I1=Ib1(1+ΔR), I2=Ib2(1−ΔR), and V1=V2=VC, the voltages V3 and V4 become: V3=VC+RCIb1+RCIb1ΔR, and V4=Vc+RCIb2−RCIb2ΔR.
Therefore, a voltage applied to the passive element Z1 becomes V3−V4=RC(Ib1−Ib2)+RC(Ib1+Ib2)ΔR. In other words, the signal components RC(Ib1+Ib2)ΔR and RC(Ib1−Ib2) are applied to the passive element Z1. RC(Ib1−Ib2) is a direct current offset voltage generated by deviation in bias current Ib1 and Ib2 contained in the current I1 and I2.
In the current amplifier circuit according to the present embodiment, since the passive element Z1 is configured by the resistor RZ11, the capacitor CZ1, and the resistor RZ12 connected in series, the direct current offset voltage is not converted into the current. Therefore, according to the present embodiment, the power consumption of the current amplifier circuit can be reduced.
In addition, the direct current offset voltage applied to the capacitor CZ1 can be converted into the current by the voltage-current conversion circuit Gm, and supplied to the transistors M1 and M2. At this time, the current is desirably supplied such that a difference between the drain current IM1 of the transistor M1 and the drain current IM2 of the transistor M2 becomes small.
For example, when the voltage-current conversion coefficient is Gm=1⁄2RC, the output current of the voltage-current conversion circuit Gm becomes ±(Ib1−Ib2)/2. When −(Ib1−Ib2)/2 is supplied to the transistor M1, the bias current of the transistor M1 becomes Ib1−(Ib1−Ib2)/2=(Ib1+Ib2)/2. In addition, when +(Ib1−Ib2)/2 is supplied to the transistor M2, the bias current of the transistor M2 becomes Ib2+(Ib1−Ib2)/2=(Ib1+Ib2)/2. In other words, the transistors M1 and M2 can be equalized in the bias current. Due to this, a direct current offset component contained in a difference between the current IM1 and the current IM2 respectively output from the output terminals T3 and T4 can be reduced.
Here, FIG. 48 is a diagram illustrating an example of the voltage-current conversion circuit Gm according to the present embodiment. As illustrated in FIG. 48, the voltage-current conversion circuit Gm includes a differential input circuit D, current mirror circuits CM1 and CM2, and current sources IGB2 and IGB3.
The differential input circuit D includes transistors MG1 and MG2, resistors RG1 and RG2, and a current source IGB1. The transistor MG1 is an NMOS transistor, having a drain terminal connected to the current mirror circuit CM1, a gate terminal connected to the input terminal InP, and a source terminal connected to one end of the resistor RG1. The transistor MG2 is an NMOS transistor, having a drain terminal connected to the current mirror circuit CM2, a gate terminal connected to the input terminal InM, and a source terminal connected to one end of the resistor RG2. The resistors RG1 and RG2 both have other ends connected to a high voltage side of the current source IGB1.
The current mirror circuit CM1 is configured by transistors MG3 and MG6, and copies the drain current IMG1 of the transistor MG1. The transistors MG3 and MG6 are PMOS transistors, having the gate terminals connected to each other. The drain terminal of the transistor MG6 is connected to the output terminal OutP and a high voltage side of the current source IGB2. Due to this, a difference between the drain current IMG1 and the current IGB2 supplied by the current source IGB2, that is, the current corresponding to a change in voltage input from the input terminal InP is output from the output terminal OutP.
The current mirror circuit CM2 is configured by transistors MG4 and MG5, and copies the drain current IMG2 of the transistor MG2. The transistors MG4 and MG5 are PMOS transistors, having the gate terminals connected to each other. The drain terminal of the transistor MG5 is connected to the output terminal OutM and a high voltage side of the current source IGB3. Due to this, a difference between the drain current IMG2 and the current IGB3 supplied by the current source IGB3, that is, the current corresponding to a change in voltage input from the input terminal InM is output from the output terminal OutM.
Here, by setting RG1=RG2=RC, IGB2=IGB3=IGB1/2, and by setting transconductances gmMG1 and gmMG2 of the transistors MG1 and MG2 to 1/gmMG1<<RC and 1/gmMG2<<RC, the voltage-current conversion coefficient Gm in the differential input circuit can be set to 1⁄2RC.
(Fourteenth Embodiment)
Next, a current amplifier circuit according to a fourteenth embodiment will be described with reference to FIGS. 49 and 50. Here, FIG. 49 is a diagram illustrating the current amplifier circuit according to the fourteenth embodiment. As illustrated in FIG. 49, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, a control circuit, a passive element Z1, and the voltage-current conversion circuit Gm. The voltage-current conversion circuit Gm of the present embodiment is different from the thirteenth embodiment in the connection method.
In the present embodiment, the output terminal OutP (the first output terminal) is connected to the other end of the resistor R1 and the control circuit at a node N1, and the output terminal OutM (the second output terminal) is connected to the other end of the resistor R2 and the control circuit at a node N2. The configurations of other components are same as the thirteenth embodiment.
In the present embodiment, a voltage V3 at a node N3 becomes V3=V1+R1(I1−IGm), and a voltage V4 at a node N4 becomes V4=V2+R2(I2+IGm). Here, −IGm and +IGm are the output current from the output terminals OutP and OutM of the voltage-current conversion circuit Gm. For example, in the case where R1=R2=RC, I1=Ib1(1+ΔR), I2=Ib2(1−ΔR), V1=V2=VC, the voltages V3 and V4 become: V3=VC+RCIb1−RCIGm+RCIb1ΔR, and V4=Vc+RCIIb2+RCIGm−RCIb2ΔR.
Therefore, a voltage applied to the passive element Z1 becomes V3−V4=RC (Ib1−Ib2)−2RCIGm+RC(Ib1+Ib2)ΔR. In other words, the signal component RC(Ib1+Ib2)ΔR, the direct current offset voltage RC(Ib1−Ib2), and a voltage −2RCIGm according to the output current of the voltage-current conversion circuit Gm are applied to the passive element Z1.
Since IGm is obtained by converting the direct current offset voltage into the current by the voltage-current conversion coefficient Gm, a relation of IGm=Gm(RC(Ib1−Ib2)−2RCIGm) is satisfied. In a case where Gm is sufficiently large and 2GmRC>>1, the current IGm becomes: IGm≈(Ib1−Ib2)/2, and the both bias currents flowing to the resistors R1 and R2 become equal to (Ib1+Ib2)/2. Due to this, it is possible to reduce the direct current offset component contained in a difference between the current IM1 and the current IM2 output from output terminals T3 and T4 respectively.
Here, FIG. 50 is a diagram illustrating an example of the voltage-current conversion circuit Gm according to the present embodiment. As illustrated in FIG. 50, the voltage-current conversion circuit Gm includes the differential input circuit D, the current mirror circuits CM1 and CM2, and current sources IGB2 and IGB3. The voltage-current conversion circuit Gm of FIG. 50 is different from the voltage-current conversion circuit Gm of FIG. 48 in the configuration of the differential input circuit D.
The differential input circuit D includes transistors MG1 and MG2 and a current source IGB1. The transistor MG1 is an NMOS transistor, having a drain terminal connected to the current mirror circuit CM1, a gate terminal connected to an input terminal InP, and a source terminal connected to a high voltage side of the current source IGB1. The transistor MG2 is an NMOS transistor, having a drain terminal connected to the current mirror circuit CM2, a gate terminal connected to an input terminal InM, and a source terminal connected to a high voltage side of the current source IGB2. In other words, the voltage-current conversion circuit Gm of FIG. 50 is different from the voltage-current conversion circuit Gm of FIG. 48, and does not include the resistors RG1 and RG2.
Therefore, in the voltage-current conversion circuit Gm of FIG. 50, a change of the output current with respect to the change of the input voltage is large compared to the voltage-current conversion circuit Gm of FIG. 48. In other words, the voltage-current conversion coefficient Gm is large. This is because, unlike the case of the thirteenth embodiment, the voltage-current conversion coefficient Gm is desirably large in the case of the present embodiment.
(Fifteenth Embodiment)
Next, a current amplifier circuit according to a fifteenth embodiment will be described with reference to FIGS. 51 to 53. Here, FIG. 51 is a diagram illustrating the current amplifier circuit according to the fifteenth embodiment. As illustrated in FIG. 51, the current amplifier circuit according to the present embodiment includes a transistor M1, a resistor R1, a transistor M2, a resistor R2, a control circuit, the passive element Z1, and a current-voltage conversion circuit. The configurations of the above components are same as the tenth embodiment. In the present embodiment, the current amplifier circuit further includes a comparison circuit and a current mirror circuit CM3.
The comparison circuit compares the output voltages from output terminals T3 and T4 with a predetermined voltage (fourth predetermined voltage), and outputs the current according to the comparison result. The comparison circuit includes transistors MB1, MB2, MB3, and MB4, a resistor RB1, and current sources IB1 and IB2.
The transistor MB1 is a PMOS transistor, having a source terminal connected to one end of the resistor RB1 and a low voltage side of the current source IB1, a gate terminal from which a predetermined bias voltage VC3 is applied, and a drain terminal connected to the drain terminal of the transistor MB4. A bias voltage VC3 is set to be lower than the bias voltage of the output voltages from the output terminals T3 and T4.
The transistor MB2 is a PMOS transistor, having a source terminal connected to the other end of the resistor RB1, the source terminal of the transistor MB3, and a low voltage side of the current source IB2, a gate terminal connected to the output terminal T4, and a drain terminal connected to the drain terminal of the transistor MB3 and the current mirror circuit CM3.
The transistor MB3 is a PMOS transistor, having a source terminal connected to the other end of the resistor RB1, the source terminal of the transistor MB2, and the low voltage side of the current source IB2, a gate terminal connected to the output terminal T3, a drain terminal connected to the drain terminal of the transistor MB2 and the current mirror circuit CM3.
The transistor MB4 is an NMOS transistor, having a source terminal grounded, a drain terminal connected to the drain terminal of the transistor MB1, and a gate terminal connected to the drain terminal.
The current mirror circuit CM3 includes transistors MB5, MB6, and MB7. The transistors MB5, MB6, and MB7 are NMOS transistors, each of which the gate terminal is connected to each other and the source terminal is grounded. In addition, the drain terminal of the transistor MB5 is connected to the drain terminals of the transistors MB2 and MB3, and the drain terminals of the transistors MB6 and MB7 are respectively connected to nodes N4 and N3.
Next, the operation of the current amplifier circuit according to the present embodiment will be described. In the following, the signal current is differentially received from input terminals T1 and T2.
First, the current-voltage conversion circuit converts the drain current IM1 and the drain current IM2 of the transistors M1 and M2 into voltages. The voltages converted by the current-voltage conversion circuit are output from the output terminals T3 and T4, and input to the comparison circuit.
Next, the comparison circuit compares the output voltages (the gate voltages of the transistors MB3 and MB2) of the output terminals T3 and T4 with a predetermined voltage. In a case where the signal components contained in the output voltages are sufficiently small, that is, the output voltages are sufficiently higher than the predetermined voltage, all the current IB2 of the current source IB2 flows to the resistor RB1, the transistors MB3 and MB2 are turned off, and the current does not flow to the current mirror circuit CM3.
On the other hand, in a case where the signal components contained in the output voltages are small and the output voltages are higher than the predetermined voltage but a difference between the voltage at the other end of the resistor RB1 and the voltage at one end of the resistor RB1 is smaller than RB1IB2, a part of current of the current IB2 of the current source IB2 starts to flow to the transistors MB2 and MB3, and flows to the current mirror circuit CM3. When the output voltages are further lowered and become smaller than the predetermined voltage, all the current IB2 of the current source IB2 and a part of the current IB1 of the current source IB1 start to flow to the transistors MB2 and MB3, and flow to the current mirror circuit CM3. Thus, the current flowing to the current mirror circuit CM3 is increased as the output voltages become small, that is, the signal components contained in the output voltages become large.
Since the output voltages are differentially input to the transistors MB2 and MB3, in a case where the signal components contained in the output voltages are sufficiently larger, one of the transistor MB2 or the transistor MB3 is turned on and the other one is turned off. Then, the drain current of the turned-on transistor is supplied to the transistor MB5.
The current output by the comparison circuit becomes the drain current IMB5 of the transistor MB5. The drain current IMB5 is copied by the transistors MB7 and MB6, and supplied from nodes N3 and N4 to the transistors M1 and M2.
With this configuration, in a case where the signal current contained in the current I1 and I2 is larger, the current amplifier circuit according to the present embodiment supplies the current to the transistors M1 and M2, and drive performance can be improved. Therefore, an amplification factor of the signal component can be improved.
As described in the first embodiment, the drain current IM1 of the transistor M1 is IM1=I1+IZ1=Ib+ΔRIb+2RCIbΔR/Z1, the drain current IM2 flowing to the transistor M2 is IM2=I2−IZ1=Ib−ΔRIb−2RCIbΔR/Z1. Therefore, in the current amplifier circuit of the first embodiment, the signal current contained in the output current from the output terminals T3 and T4 is not possible to become larger than the bias current Ib.
However, according to the present embodiment, since the current can be supplied to the transistors M1 and M2 through the current mirror circuit CM3, it is possible to make the signal current contained in the output current larger than the bias current Ib.
In addition, the output current from the comparison circuit is smoothly changed by connecting the resistor RB1 between the transistor MB1 and the transistors MB2 and MB3, and the deformation of the output current from the comparison circuit can be suppressed.
FIG. 52 is a diagram illustrating another example of the current amplifier circuit according to the present embodiment. In FIG. 52, the drain terminal of the transistor MB2 of the comparison circuit and the drain terminal of the transistor MB3 are not connected, and they are connected to the current mirror circuit CM3, respectively. The current mirror circuit CM3 includes a first current mirror circuit CM31 and a second current mirror circuit CM32.
The first current mirror circuit CM31 includes the transistor MB5 and the transistor MB6. The transistor MB5 has a drain terminal connected to a gate terminal and the drain terminal of the transistor MB2, the gate terminal connected to the gate terminal of the transistor MB6, and a source terminal grounded. The transistor MB6 has a drain terminal connected to a node N4, a gate terminal connected to the gate terminal of the transistor MB5, and a source terminal grounded. A first current mirror circuit CM31 copies the drain current IMB2 of the transistor MB2 and supplies the current from the node N4 to the transistor M2.
The second current mirror circuit CM32 includes a transistor MB7 and a transistor MB8. The transistor MB8 has a drain terminal connected to a gate terminal and the drain terminal of the transistor MB3, the gate terminal connected to the gate terminal of the transistor MB7, and a source terminal grounded. The transistor MB7 has a drain terminal connected to a node N3, a gate terminal connected to the gate terminal of the transistor MB8, and a source terminal grounded. A second current mirror circuit CM32 copies the drain current IMB3 of the transistor MB3 and supplies the current from the node N3 to the transistor M1.
The configurations of other components are same as the current amplifier circuit of FIG. 51. With this configuration, it is possible to supply the current only to the transistor M1 or the transistor M2 outputting the lower voltage in the output voltages from the output terminals T3 and T4.
FIG. 53 is a diagram illustrating another example of the current amplifier circuit according to the present embodiment. In FIG. 53, the comparison circuit further includes a resistor RB2 and a current source IB3. The transistor MB2 has a source terminal connected to one end of the resistor RB1 and a lower voltage side of the current source IB2, a gate terminal connected to the output terminal T4, and a drain terminal connected to the current mirror circuit CM31. The transistor MB3 has a source terminal connected to one end of the resistor RB2 and a lower voltage side of the current source IB3, a gate terminal connected to the output terminal T3, and a drain terminal connected to the current mirror circuit CM32. The configurations of other components are same as FIG. 52.
With this configuration, it is possible to supply the current only to the transistor M1 or the transistor M2 outputting the lower voltage in the output voltages from the output terminals T3 and T4. In addition, it is possible to separately set a voltage to be used for comparison with the output voltage from the output terminal T3 and a voltage to be used for comparison with the output voltage from the output terminal T4. Furthermore, it is possible to separately set current to be supplied from the node N3 and current to be supplied from the node N4.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

## Claims

1. A current amplifier circuit, comprising:
a first transistor having a first terminal, a second terminal, and a control terminal;
a first resistor having one end connected to the first terminal of the first transistor;
a second transistor having a first terminal, a second terminal, and a control terminal;
a second resistor having one end connected to the first terminal of the second transistor;
a first passive element connected between the first terminal of the first transistor and the first terminal of the second transistor; and
a control circuit to control at least one of voltage at the control terminal of the first transistor and voltage at the control terminal of the second transistor such that voltage at an other end of the first resistor becomes equal to a first predetermined voltage and voltage at an other end of the second resistor becomes equal to a second predetermined voltage.

2. The circuit according to claim 1, wherein the first predetermined voltage is equal to the second predetermined voltage.

3. The circuit according to claim 1, further comprising:
a third transistor having a first terminal, a second terminal, and a control terminal connected to the control terminal of the first transistor;
a fourth transistor having a first terminal, a second terminal, and a control terminal connected to the control terminal of the second transistor; and
a second passive element connected between the first terminal of the third transistor and the first terminal of the fourth transistor,
wherein
the second terminal of the third transistor is connected to the second terminal of the first transistor, and
the second terminal of the fourth transistor is connected to the second terminal of the second transistor.

4. The circuit according to claim 1, further comprising:
a third transistor having a first terminal, a second terminal, and a control terminal connected to the first terminal of the first transistor;
a fourth transistor having a first terminal, a second terminal, and a control terminal connected to the first terminal of the second transistor; and
a second passive element connected between the first terminal of the third transistor and the first terminal of the fourth transistor,
wherein
the second terminal of the third transistor is connected to the second terminal of the first transistor, and
the second terminal of the fourth transistor is connected to the second terminal of the second transistor.

5. The circuit according to claim 1, comprising a switching circuit to switch a path such that current flowing in the first transistor and current flowing in the second transistor alternately is switched.

6. The circuit according to claim 5, the switching circuit comprising:
a first switch to switch the path between a path of current output from the second terminal of the first transistor and a path of current output from the second terminal of the second transistor; and
a second switch to switch the path between a path of current received from the other end of the first resistor and a path of current received from the other end of the second resistor.

7. The circuit according to claim 5, the switching circuit comprising:
a first switch to switch the path between a path of current output from the second terminal of the first transistor and a path of current output from the second terminal of the second transistor;
a third switch to switch the path between a path of current output from the one end of the first resistor and a path of current output from the one end of the second resistor;
a fourth switch to switch a path of voltage received in the control circuit in order to control voltage at a gate terminal of the first transistor; and
a fifth switch to switch a path of voltage received in the control circuit in order to control voltage at a gate terminal of the second transistor.

8. The circuit according to claim 1, further comprising:
a fifth transistor having a first terminal connected to a first input terminal, a second terminal connected to the other end of the first resistor, and a control terminal applied with a third predetermined voltage, and
a sixth transistor having a first terminal connected to a second input terminal, a second terminal connected to the other end of the second resistor, and a control terminal applied with the third predetermined voltage.

9. The circuit according to claim 1, wherein
the first passive element includes
a third resistor having one end connected to the first terminal of the first transistor,
a fourth resistor having one end connected to the first terminal of the second transistor, and
a capacitor connected between an other end of the third resistor and an other end of the fourth resistor,
the circuit further comprising:
a voltage-current conversion circuit having a first output terminal connected to the one end of the third resistor, a first input terminal connected to the other end of the third resistor, a second output terminal connected to the one end of the fourth resistor, and a second input terminal connected to the other end of the fourth resistor.

10. The circuit according to claim 1, wherein
the first passive element includes
a third resistor having one end connected to the first terminal of the first transistor,
a fourth resistor having one end connected to the first terminal of the second transistor, and
a capacitor connected between an other end of the third resistor and an other end of the fourth resistor,
the circuit further comprising:
a voltage-current conversion circuit having a first output terminal connected to the other end of the first resistor, a first input terminal connected to the other end of the third resistor, a second output terminal connected to the other end of the second resistor, and a second input terminal connected to the other end of the fourth resistor.

11. The circuit according to claim 1, further comprising:
a current-voltage conversion circuit to convert drain current of the first transistor and the second transistor into voltage;
a comparison circuit to compare the voltage converted by the current-voltage conversion circuit with a fourth predetermined voltage; and
a current mirror circuit to supply current according to a comparison result of the comparison circuit to at least one of the first transistor and the second transistor.

12. The circuit according to claim 1, wherein impedance of the first passive element is variable.

13. The circuit according to claim 1, wherein the control terminal is a gate terminal or a base terminal, the first terminal is a source terminal or an emitter terminal, and the second terminal is a drain terminal or a collector terminal.

14. An integrator, comprising:
a current amplifier circuit according to claim 1; and
a capacitor element to integrate an output signal of the current amplifier circuit.

15. The integrator according to claim 14, wherein the capacitor element is formed including capacitor connected between the second terminal of the first transistor and the second terminal of the second transistor.

16. The integrator according to claim 14, wherein the capacitor element is formed including a first capacitor connected to the second terminal of the first transistor, and a second capacitor connected to the second terminal of the second transistor.

17. An AD converter, comprising:
a current amplifier circuit according to claim 1;
a current-voltage conversion circuit to convert an output signal of the current amplifier circuit to a voltage signal; and
an AD conversion circuit to convert the voltage signal to a digital signal.

18. A current amplifier circuit, comprising:
a first transistor having a first terminal, a second terminal, and a control terminal;
a first resistor having one end connected to the first terminal of the first transistor;
a first passive element connected between the first terminal of the first transistor and reference potential;
a control circuit to control voltage at the control terminal of the first transistor such that the other end of the first resistor becomes a first predetermined voltage:
a second transistor having a first terminal connected to an input terminal, and
a second terminal connected to an other end of the first resistor, and a control terminal applied with a second predetermined voltage.

19. A current amplifier circuit, comprising:
a first transistor having a first terminal, a second terminal, and a control terminal;
a first resistor having one end connected to the first terminal of the first transistor;
a first passive element connected between the first terminal of the first transistor and reference potential; and
a control circuit to control voltage at the control terminal of the first transistor such that the other end of the first resistor becomes a first predetermined voltage, wherein the first passive element is formed including at least a capacitor.