Reference voltage generator

A reference voltage generator includes a voltage generation circuit, an amplifier, a diode unit and a transistor. The voltage generation circuit includes an output terminal for outputting a reference voltage, a first terminal having an operational voltage, and a second terminal. The amplifier includes an input terminal coupled to the first terminal of the voltage generation circuit, an output terminal, a first terminal coupled to a first voltage terminal, and a second terminal. The diode unit includes a first terminal coupled to the second terminal of the amplifier, and a second terminal coupled to the second terminal of the voltage generation circuit and a second voltage terminal. The transistor includes a first terminal coupled to the first terminal of the amplifier, a second terminal coupled to the output terminal of the voltage generation circuit, and a control terminal coupled to the output terminal of the amplifier.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Taiwan Patent Application No. 107100166, filed Jan. 3, 2018, and incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a reference voltage generator, and more particularly, a reference voltage generator for providing a substantially constant reference voltage being substantially unaffected by temperature.

BACKGROUND

In the field of electrical circuit application, a reference voltage is usually provided by using a reference voltage generator such as a bandgap voltage generator. However, in a conventional reference voltage generator, a control voltage may be as low as 1.2 volt. Then, an operational amplifier may be used to amplify the 1.2 volts voltage to generate a 3.3 volts reference voltage. In this sort of circuit structure, an operational amplifier is necessary, and a compensation capacitor of the operational amplifier will make it difficult to reduce circuit area. In addition, it is also difficult to improve the power supply rejection ratio (PSRR) when using a conventional reference voltage generator. In other words, the provided reference voltage is easily affected by noise of a power supply. When manufacturing a conventional reference voltage generator, limitation of process is a problem. For example, it is hard to use a Gallium arsenide (GaAs) Heterojunction Bipolar Transistor (HBT) process. For example, in a conventional reference voltage generator, a current source including P-type metal oxide semiconductor field-effect transistor (MOSFET) is often required, and a circuit including N-type MOSFET is also needed. Hence, a GaAs process is hard to be used in manufacture.

SUMMARY

An embodiment of the present invention provides a reference voltage generator. The reference voltage generator includes a first resistor, a first transistor, a second transistor, a third transistor, a fourth transistor, a second resistor, a third resistor, a fourth resistor, a fifth transistor, a diode unit and a sixth transistor. The first resistor includes a first terminal and a second terminal. The first transistor includes a first terminal, a second terminal coupled to the second terminal of the first resistor, and a control terminal coupled to an operation node. The second transistor includes a first terminal, a second terminal coupled to the first terminal of the first resistor, and a control terminal coupled to the operation node. The third transistor includes a first terminal, a second terminal coupled to the first terminal of the first transistor, and a control terminal coupled to the first terminal of the third transistor. The fourth transistor includes a first terminal, a second terminal coupled to the first terminal of the second transistor, and a control terminal coupled to the control terminal of the third transistor. The second resistor includes a first terminal coupled to an output terminal for outputting a reference voltage, and a second terminal coupled to the first terminal of the fourth transistor. The third resistor includes a first terminal coupled to the first terminal of the second resistor, and a second terminal coupled to the first terminal of the third transistor. The fourth resistor includes a first terminal and a second terminal. The fifth transistor includes a first terminal coupled to the second terminal of the fourth resistor, a second terminal, and a control terminal coupled to the first terminal of the fourth transistor. The diode unit includes a first terminal coupled to the second terminal of the fifth transistor, and a second terminal coupled to the second terminal of the first resistor. The sixth transistor includes a first terminal coupled to the first terminal of the fourth resistor, a second terminal coupled to the first terminal of the second resistor, and a control terminal coupled to the second terminal of the fourth resistor. The operation node is coupled to the first terminal of the first transistor or the first terminal of the second transistor.

Another embodiment of the present invention provides a reference voltage generator. The reference voltage generator includes a constant voltage generation circuit, an amplifier, a diode unit and a transistor. The constant voltage generation circuit includes an output terminal for outputting a reference voltage, a first terminal having a first operational voltage, and a second terminal. The amplifier includes an input terminal coupled to the first terminal of the constant voltage generation circuit, an output terminal, a first terminal coupled to a first voltage terminal, and a second terminal. The diode unit includes a first terminal coupled to the second terminal of the amplifier, and a second terminal coupled to the second terminal of the constant voltage generation circuit and a second voltage terminal. The transistor includes a first terminal coupled to the first terminal of the amplifier, a second terminal coupled to the output terminal of the constant voltage generation circuit, and a control terminal coupled to the output terminal of the amplifier.

DETAILED DESCRIPTION

FIG. 1illustrates a reference voltage generator10according to an embodiment. The reference voltage generator10may include transistors Q1to Q4and resistors R11to R14. The transistor Q1may include a first terminal, a control terminal and a second terminal, and the control terminal is coupled to the first terminal. The transistor Q2may include a first terminal, a control terminal and a second terminal, and the control terminal is coupled to the control terminal of the transistor Q1. The resistor R11may include a first terminal and a second terminal, the first terminal is coupled to the second terminal of the transistor Q2, and the second terminal is coupled to the second terminal of the transistor Q1and a voltage terminal Vg. The resistor R12may include a first terminal and a second terminal where the first terminal is coupled to an output terminal Nout for outputting a reference voltage VBG, and the second terminal is coupled to the first terminal of the transistor Q2. The reference voltage VBGmay be a bandgap voltage. The resistor R13may include a first terminal and a second terminal where the first terminal is coupled to the output terminal Nout and the second terminal is coupled to the first terminal of the transistor Q1. The transistor Q4may include a first terminal, a control terminal and a second terminal where the first terminal is coupled to a voltage terminal Vh, and the second terminal is coupled to the first terminal of the resistor R12and the first terminal of the resistor R13. The resistor R14may include a first terminal and a second terminal where the first terminal is coupled to the voltage terminal Vh, and the second terminal is coupled to the control terminal of the transistor Q4. The transistor Q3may include a first terminal, a control terminal and a second terminal where the first terminal is coupled to the second terminal of the resistor R14, the control terminal is coupled to the first terminal of the transistor Q2, and the second terminal is coupled to the second terminal of the transistor Q1. The resistors R12and R13may have identical resistance substantially. The first terminal of the transistor Q2(i.e. the second terminal of the resistor R12) and the first terminal of the transistor Q1(i.e. the second terminal of the resistor R13) may have an identical voltage Vx. There may be a voltage Vbelacross the control terminal and the second terminal of the transistor Q1. There may be a voltage Vbe2across the control terminal and the second terminal of the transistor Q2. There may be a voltage ΔV11across the resistor R11. There may be a voltage ΔV12across the resistor R12. Currents flowing through the resistors R12and R13may be I12and I13respectively. The current I12may be identical to the current I13substantially, and it can be expressed as I12=I13=1. The saturation currents of the transistors Q1and Q2may be currents IS1and IS2respectively. The area of the transistor Q2may be adjusted to be four times the area of the transistor Q1, so the equation IS2=4×IS1may be derived. In this case, the multiplier four is an example. According to another embodiment, the area of the transistor Q2may be adjusted to be n times the area of the transistor Q1. The following embodiments may be used to adjust the area of the transistor Q2to be n times the area of the transistor Q1. For example, on a circuit layout, the transistor Q1may be copied n times to form the transistor Q2. In another example, the number of the transistor Q2may be n times the number of the transistor Q1, where n is a positive integer.

According to the above description andFIG. 1, the following derivation may be obtained.

In the above equations, VTmay be a thermal voltage, k may be the Boltzmann constant, T may be an absolute temperature, and q may be elementary electric charge. Hence, it may be derived that ΔV11is a positive temperature coefficient. Since the cross voltage Vbelis a negative temperature coefficient, the reference voltage VBGmay be kept without being affected by temperature substantially by adjusting a ration of R12/R11. For example, when using a GaAs process, the reference voltage VBGinFIG. 1may be 1.6 volts approximately.

FIG. 2illustrates a reference voltage generator100according to another embodiment. The reference voltage generator100may include resistors R1to R4, transistors T1to T6and a diode unit D1. The transistors T1and T2inFIG. 2may be similar to the transistors Q1and Q2inFIG. 1, but the transistors T1and T2may be coupled to the transistors T3and T4respectively to form stack structures. As shown inFIG. 2, the resistor R1may include a first terminal and a second terminal. The transistor T1may include a first terminal, a second terminal and a control terminal where the second terminal is coupled to the second terminal of the resistor R1, and the control terminal is coupled to an operation node N1. The transistor T2may include a first terminal, a second terminal and a control terminal where the second terminal is coupled to the first terminal of the resistor R1, and the control terminal is coupled to the operation node N1. The transistor T3may include a first terminal, a second terminal and a control terminal where the first terminal has an operational voltage Vy, the second terminal is coupled to the first terminal of the transistor T1, and a control terminal is coupled to the first terminal of the transistor T3. The transistor T4may include a first terminal, a second terminal and a control terminal where the first terminal has an operational voltage Vx, the second terminal is coupled to the first terminal of the transistor T2, and the control terminal is coupled to the control terminal of the transistor T3. The resistor R2may include a first terminal and a second terminal where the first terminal is coupled to an output terminal Nout for outputting a reference voltage Vr, and the second terminal is coupled to the first terminal of the transistor T4. The resistor R3may include a first terminal and a second terminal where the first terminal is coupled to the first terminal of the resistor R2, and a second terminal is coupled to the first terminal of the transistor T3. The resistor R4may include a first terminal and a second terminal. The transistor T5may include a first terminal, a second terminal and a control terminal where the first terminal is coupled to the second terminal of the resistor R4, and the control terminal is coupled to the first terminal of the transistor T4. The diode unit D1may include a first terminal and a second terminal where the first terminal is coupled to the second terminal of the transistor T5, and the second terminal is coupled to the second terminal of the resistor R1. The transistor T6may include a first terminal, a second terminal and a control terminal where the first terminal is coupled to the first terminal of the resistor R4, the second terminal is coupled to the first terminal of the resistor R2, and the control terminal is coupled to the second terminal of the resistor R4. As shown inFIG. 2, the first terminal of the resistor R4may be coupled to a voltage terminal Vh, and the second terminal of the resistor R1may be coupled to a voltage terminal Vg. According to an embodiment, a voltage of the voltage terminal Vh may be higher than a voltage of the voltage terminal Vg. For example, the voltage terminal Vh may be a supply voltage terminal, and the voltage terminal Vg may be a low voltage terminal or a ground terminal. When being operated, the control terminal of the transistor T6may have a higher voltage than the second terminal of the transistor T6. A unidirectional feedback from the control terminal of the transistor T6to the second terminal of the transistor T6may make the operational voltages Vx and Vy be unaffected by changes of the reference voltage Vr. The transistor T6may hence have an effect of isolation.

According to an embodiment, the operation node N1may be coupled to the first terminal of the transistor T1or the first terminal of the transistor T2. InFIG. 2, the operation node N1is coupled to the first terminal of the transistor T1.FIG. 3illustrates a reference voltage generator200according to another embodiment. The reference voltage generator200may be similar to the reference voltage generator100, but in the reference voltage generator200, the operation node N1may be coupled to the first terminal of the transistor N2.

According to embodiments, at least one of the transistors T1to T5may be a bipolar junction transistor (BJT), and the BJT may be an NPN-type transistor. The transistor T6may be a field effect transistor (FET) or a BJT. When a transistor is a BJT, the first terminal may be a collector terminal, the second terminal may be an emitter terminal, and the control terminal may be a base terminal. When a transistor is a FET, the first terminal may be a drain terminal, the second terminal may be a source terminal, and the control terminal may be a gate terminal. The reference voltage generators100and200may be manufactured using a Bipolar Field Effect Transistor (BIFET) process or a bipolar process. According to an embodiment, the reference voltage generators100and200may be formed using Heterojunction Bipolar Transistor (HBT) process such as a GaAs HBT process. According to embodiments, the used HBT process may be an III-V process (e.g. a GaAs process) or an IV-IV process (e.g. a SiGe process). According to embodiments, the reference voltage generators100and200may be manufactured using a high-electron-mobility transistor (HEMT) process (e.g. a depletion-mode pseudomorphic HEMT (D-mode pHEMT)) so as to increase voltage headroom of the circuit.

According to an embodiment, the first terminal of the transistor T3and the first terminal of the transistor T4may have a substantially identical voltage. In other words, the operational voltages Vx and Vy may be identical substantially, that is, Vx=Vy. In addition, the current I1flowing through the resistor R2may be adjusted to be substantially identical to the current I2flowing through the resistor R3, so the current I1may be substantially identical to the current I2. A negative feedback path formed by the transistor T5, the resistor R4and the diode unit D1may reduce the influence of the voltage terminal Vh on the reference voltage Vr, so the PSRR may be improved.

InFIG. 2andFIG. 3, the resistors R2and R3may have a substantially identical resistance. ComparingFIG. 1withFIG. 2andFIG. 3, the transistors Q1, Q2, Q3and Q4shown inFIG. 1may be corresponding to the transistors T1, T2, T5and T6shown inFIG. 2andFIG. 3. The resistance of one of the resistors R2and R3may be twice the resistance of one of the resistors R12and R13. In other words, it may expressed as R12=R13=R, and R2=R3=R×2. InFIG. 2andFIG. 3, The area of the transistor T2may be substantially four times the area of the transistor T1.

According toFIG. 2andFIG. 3, the following calculation may be derived. A parameter K may be obtained by dividing the resistance of the resistor R2by the resistance of the resistor R1, and it can be expressed as K=R2/R1. There may be a voltage ΔV across the two terminals of the resistor R1. There may be a voltage ΔVbelacross the control terminal and the second terminal of the transistor T1. The voltage ΔV inFIG. 2may be corresponding to the voltage ΔV11inFIG. 1, so the voltage ΔV may be a positive temperature coefficient increasing when the temperature is raised. The voltage VbelofFIG. 2may be corresponding to the voltage VbelofFIG. 1, so the voltage Vbelmay be a negative temperature coefficient decreasing when the temperature is raised. By adjusting the parameter K, a sum of the voltage Vbeland a product of the parameter K and the voltage ΔV (that can be expressed as K×ΔV+Vbel) may be substantially unaffected by temperature. Furthermore, the sum may be proportional to the reference voltage Vr. Because the reference voltage generator100ofFIG. 2has two more additional transistors T3and T4than the reference voltage generator10ofFIG. 1, the reference voltage generator100may have a stack structure, and the reference voltage VBGofFIG. 1may be level shifted to generate the reference voltage Vr ofFIG. 2. According to an embodiment, the reference voltage Vr ofFIG. 2may be substantially twice the reference voltage VBGofFIG. 1, and it may be expressed as Vr≈m VBG×2. For example, when a GaAs process is used, the reference voltage VBGofFIG. 1may be 1.6 volts approximately, so the reference voltage Vr outputted from the output terminal Nout ofFIG. 2may substantially be 3.3 volts approximately. Because 3.3 volts may be a commonly used reference voltage, the voltage may be provided for related applications. Likewise, inFIG. 3, the outputted reference voltage Vr may also be 3.3 volts approximately and provided for related applications.

FIG. 4illustrates the structure of the diode unit D1inFIG. 2andFIG. 3according to an embodiment. As shown inFIG. 4, the diode unit D1may include a transistor T7. The transistor T7may include a first terminal, a second terminal and a control terminal where the first terminal is coupled to the first terminal of the diode unit D1, the second terminal is coupled to the second terminal of the diode unit D1, and the control terminal is coupled to the first terminal of the transistor T7. According to embodiments, the transistor T7may be a FET or a BJT, and the BJT may be an NPN-type transistor. When the transistor T7is a BJT, the first terminal may be a collector terminal, the second terminal may be an emitter terminal, and the control terminal may be a base terminal. When the transistor T7is a FET, the first terminal may be a drain terminal, the second terminal may be a source terminal, and the control terminal may be a gate terminal.

FIG. 5illustrates the structure of the diode unit D1inFIG. 2andFIG. 3according to another embodiment. The diode unit D1may include a diode D. The diode D may include a first terminal and a second terminal where the first terminal is coupled to the first terminal of the diode unit D1, and the second terminal is coupled to the second terminal of the diode unit D1. For example, the first terminal of the diode D may be an anode terminal, and the second terminal may be a cathode terminal.

FIG. 6illustrates a reference voltage generator600according to an embodiment. The reference voltage generator600may include a constant voltage generation circuit610, an amplifier620, a diode unit D1and a transistor T6. The constant voltage generation circuit610may include an output terminal Nout, a first terminal and a second terminal where the output terminal Nout is used for outputting a reference voltage Vr and the first terminal may have an operational voltage Vx. The amplifier620may include an input terminal, an output terminal, a first terminal and a second terminal where the input terminal is coupled to the first terminal of the constant voltage generation circuit610, and the first terminal is coupled to a voltage terminal Vh. The diode unit D1may include a first terminal and a second terminal where the first terminal is coupled to the second terminal of the amplifier620, and the second terminal is coupled to the second terminal of the constant voltage generation circuit610and a voltage terminal Vg. The transistor T6may include a first terminal, a second terminal and a control terminal where the first terminal is coupled to the first terminal of the amplifier620, the second terminal is coupled to the output terminal Nout of the constant voltage generation circuit610, and the control terminal is coupled to the output terminal of the amplifier620.

For example, the constant voltage generation circuit610inFIG. 6may include the transistors T1to T4and the resistors R1to R3ofFIG. 2andFIG. 3. The amplifier620may include the transistor T5and the resistor R4as an example. The couplings of the components may be as shown inFIG. 2orFIG. 3. In the circuits, the first terminal of the resistor R2ofFIG. 2orFIG. 3may be coupled to the output terminal of the constant voltage generation circuit610. The first terminal of the transistor T4may be coupled to the first terminal of the constant voltage generation circuit610. The second terminal of the resistor R1may be coupled to the second terminal of the constant voltage generation circuit610. In the circuit, the first terminal of the resistor R4ofFIG. 2orFIG. 3may be coupled to the first terminal of the amplifier620. The second terminal of the resistor R4ofFIG. 2orFIG. 3may be coupled to the output terminal of the amplifier620. The second terminal of the transistor T5may be coupled to the second terminal of the amplifier620. The control terminal of the transistor T5may be coupled to the input terminal of the amplifier620. The diode unit D1and the transistor T6ofFIG. 6may be corresponding to the diode unit D1and the transistor T6ofFIG. 2andFIG. 3. In addition, other suitable circuit structures are within the scope of embodiments of the application.

In summary, a reference voltage generator provided by an embodiment may have an effect of low dropout voltage without using an operational amplifier, so the circuit area occupied by compensation capacitors may be reduced. Moreover, the PSRR may be improved so as to reduce the influence of the noise of a power supply terminal. An external current source may be unneeded when using the reference voltage generator of an embodiment, so use of different types of transistors is avoided. This may lead to less limitations of the manufacture process. For example, it may be allowed to use a GaAs HBT process. A reference voltage generators provided by an embodiment may have a larger voltage headroom, and an outputted reference voltage may be substantially less sensitive to temperature. For example, a reference voltage may be provided substantially stably under an operating temperature range of −45° C. to 85° C. Hence, it is beneficial for alleviating engineering problems in the field by using a reference voltage generator provided by an embodiment.