Reference bias generating circuit

A reference current bias circuit includes a self-bias circuit configured to provide a bias current to an amplifier; a basic bandgap circuit coupled to inputs of the amplifier; a startup circuit configured to support an initial operation of the amplifier; a temperature compensator configured to include a first mirroring unit for mirroring current according to a positive temperature coefficient characteristic from the basic bandgap circuit; and a second mirroring unit for mirroring current according to a negative temperature coefficient characteristic from the basic bandgap circuit, and to provide a reference current by combining the current of the first mirroring unit and the current of the second mirroring unit; and a reference current mirroring unit configured to generate reference current biases based on the reference current from the temperature compensator.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority of Korean Patent Application No. 10-2008-0123456, filed on Dec. 5, 2008, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reference bias generating circuit; and, more particularly, to a low-voltage reference bias generating circuit.

2. Description of Related Art

In general, a circuit of an electronic system is formed in an integrated chip including a plurality of active elements and passive elements. Each of the elements in the electronic system requires a reference bias circuit. The reference bias circuit generates a reference voltage and a reference current for stable operation of the electronic system. Therefore, the bias circuit is an important element in an electronic system.

Overall power consumption of an electronic system has increased due to the diversification of applications and the increments of functions to provide to a user. Accordingly, it is important to improve the battery efficiency of an electronic system that is not continuously applied with a predetermined voltage. In order to reduce the power consumption, circuits with a low supply voltage have to be developed and a reference bias circuit has to be also advanced to operate in a low supply voltage.

In general, elements of an electronic system have properties that change according to a temperature. For example, passive elements such as resistors or inductors have a resistance value increasing in proportion to a temperature. Also, a semiconductor element having particular conjunction (PN junction) such as a diode or a transistor has a resistance value increasing in reverse proportion to a temperature. Such elements may have linear property or non-linear property for the temperature. Accordingly, a reference bias circuit is also generally influenced by the temperature. In a system with various ICs, the increment of an internal temperature or an external temperature influences badly the performance of an electronic system. Therefore, there has been a demand for a bias circuit that can be driven with a low supply voltage and less sensitive to a temperature variation.

Hereinafter, a bandgap bias circuit for generating uniform bias currents/voltages regardless of temperature variation will be described.

FIG. 1is a conventional bandgap bias circuit for generating a uniform bias voltage.

Referring toFIG. 1, the conventional bandgap bias circuit includes first to third transistors MM1, MM2, and MM3, first to third bipolar junction transistors Q1, Q2, and Q3, and an OP-AMP.

Here, a voltage ΔVBEapplied to a first resistor RR1is a difference between a base-emitter voltage VBE1of the first bipolar junction transistor Q1and a base-emitter voltage VBE2of the second bipolar junction transistor Q2.

A current I3flowing to the third transistor MM3by mirroring the RR1current is proportional to the current flowing through the first resistor RR1. Therefore, a reference voltage Vrefoutputted from the bandgap bias circuit is the sum of a voltage V1applied to both terminals of a second resistor RR2and a base-emitter voltage VBE3between the emitter and base of the third bipolar junction transistor Q3.

Here, the voltage V1applied to the both terminals of the second resistor RR2can be expressed as Eq. 1 based on the Ohm's law.
V1=I3×RR2Eq. 1

The voltage VBE3between the emitter and the base of the third bipolar junction transistor Q3is referred to as ‘V2’. As described above, each of the elements has its property changing according to temperature. Therefore, the reference voltage Vrefaccording to the temperature can be expressed as Eq. 2.
Vref32α1V1+α2V2Eq. 2

In Eq. 2, α1denotes a temperature coefficient for a resistance value of the second resistor RR2, and α2denotes a temperature coefficient about VBE3of the third bipolar junction transistor Q3.

In order to satisfy the reference voltage having a constant value according to the temperature, the differentiation of Eq. 2 for temperature must have relation of Eq. 3.

The sum of two differential values in Eq. 3 will be 0 if two values are the same with the opposite sign.

In a conventional bandgap bias circuit, a diode-PN junction voltage VBEof a bipolar junction transistor has negative relation in proportion to temperature variation. A base-emitter voltage difference of two bipolar junction transistors having a different current amount has positive relation in proportion to temperature variation due to a difference of voltage gradients. Therefore, a reference voltage Vrefgenerated from a bandgap bias circuit can be expressed as Eq. 4.

The reference voltage Vrefgenerated from this bandgap bias circuit is decided based on the sum of the base-emitter voltage difference ΔVBEand the base-emitter voltage VBE3of the third bipolar junction transistor Q3. Here, it is possible to provide a low reference voltage less sensitive to temperature variation by attenuating a temperature variable which can be controlled a resistance ratio RR1/RR2and a coefficient k having a temperature characteristic gradient opposite to the base-emitter voltage VBE3of the third bipolar junction transistor Q3.

However, such a bandgap bias circuit according to the prior art has an excellent temperature compensation characteristic at around a reference voltage of 1.25V theoretically as shown in Eq. 4. Therefore, it cannot be applied to circuits using a supply voltage lower than 1.2V. So, there is a demand for developing an apparatus and method for stably and uniformly providing a reference current and a reference voltage even in a low supply voltage such as lower than 1.2V.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to providing a reference bias generating circuit for providing a stable voltage.

Another embodiment of the present invention is directed to providing a reference bias generating circuit for providing a stable current.

Another embodiment of the present invention is directed to providing a reference bias circuit for reducing power consumption.

Another embodiment of the present invention is directed to providing a reference bias circuit for reducing a chip area.

In accordance with an aspect of the present invention, there is provided a reference current bias circuit, including a self-bias circuit configured to provide a bias current to an amplifier; a basic bandgap circuit coupled to inputs of the amplifier; a startup circuit configured to support an initial operation of the amplifier; a temperature compensator configured to include a first mirroring unit for mirroring current according to a positive temperature coefficient characteristic from the basic bandgap circuit; and a second mirroring unit for mirroring current according to a negative temperature coefficient characteristic from the basic bandgap circuit, and to provide a reference current by combining the current of the first mirroring unit and the current of the second mirroring unit; and a reference current mirroring unit configured to generate reference current biases based on the reference current from the temperature compensator.

In accordance with another aspect of the present invention, there is provided a reference voltage bias circuit including a self-bias circuit configured to provide a bias current to an amplifier; a basic bandgap circuit coupled to inputs of the amplifier; a startup circuit configured to support an initial operation of the amplifier; a temperature compensator configured to include a first mirroring unit for mirroring current according to a positive temperature coefficient characteristic from the basic bandgap circuit, a second mirroring unit for mirroring current according to a negative temperature coefficient characteristic from the basic bandgap circuit, and to provide a reference current by combining the current of the first mirroring unit and the current of the second mirroring unit; and a reference voltage providing unit configured to generate reference voltage biases based on the reference current from the temperature compensator.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The advantages, features and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.

FIG. 2Ais a diagram illustrating a reference current bias circuit for low supply voltage in accordance with an embodiment of the present invention.

Referring toFIG. 2A, the reference current bias circuit according to the present embodiment includes a start-up circuit100and a bandgap reference current circuit200. The start-up circuit100supports an initial operation of the reference current bias circuit to quickly reach a normal state without falling into an abnormal zero state. The bandgap reference current circuit200includes an amplifier210, a self-bias unit220for driving the amplifier210, a basic bandgap unit230having two input terminals, a temperature compensator240for eliminating a temperature variation characteristic, and a reference current mirroring unit250for generating reference currents. The bandgap reference current circuit200stably provides reference currents in a low supply voltage although temperature changes.

The basic bandgap unit230includes a fifth transistor M5, a first diode D1, a ninth transistor M9, a second resistor R2, and a second diode D2. The amplifier210includes five transistors M2, M3, M4, M7and M8, and the self-bias unit220includes two transistors M1and M6and a first resistor R1. The temperature compensator240includes four transistors M10to M13and third and fourth resistors R3and R4. The reference current mirroring unit250includes a fourteenth transistor M14and n transistors for mirroring the temperature compensated current of the fourteenth transistor M14to provide the mirrored bias currents to sub circuit blocks.

Hereinafter, the operation of the bandgap reference current circuit200according to the present embodiment will be described with reference toFIG. 2A.

When power is applied to the bandgap reference current circuit200, the start-up circuit100prevents the abnormal state of the amplifier210and the self-bias circuit220gives a bias current to the amplifier210by a feedback loop. Since the start-up circuit100is well known to those skilled in the prior art, detail description thereof is omitted. The amplifier210makes two nodes V1and V2of The basic bandgap circuit230to be same. Therefore, a voltage applied to the second resistor R2is equal to a value obtained by subtracting a voltage V3of the second diode D2from a voltage V1of the first diode D1. Herein, currents flowing through the first and second diodes D1and D2are controlled by a junction area ratio of each diode. For example, if the junction area ratio of the first and second diodes D1and D2is 1:P, current as much as P flows through the second diode D2and current as much as 1 flows through the first diode D1. The junction area ratio of the diodes can be controlled by the number of the parallel connections of a diode with same area.

In order to reduce the number of used diodes, a current i1flowing through the fifth transistor M5and a current i2flowing through the ninth transistor M9have a current ratio of K:1 where K>1. That is, if the current i2flowing through the ninth transistor M9is 1, the current i1flowing through the fifth transistor M5is K. It can be done by controlling the dimension W/L of M5and M9. The current i2of the ninth transistor M9is equal to the current of the second resistor R2and can be calculated by Ohm's law. The voltage of the second resistor R2can be expressed as difference between the voltage V2and the voltage V3due to the voltage V2is same with the voltage V1. If the ninth transistor M9and the thirteenth transistor M13have a same dimension W/L, the current i2flowing through the ninth transistor M9is mirrored to the thirteenth transistor M13with the same current. Such the current i5of the thirteenth transistor M13can be expressed as Eq. 5.

Since the second resistor R2is a passive element and it has a positive characteristic proportional to a temperature.

The voltage V3of the second diode D2is inputted to a gate of the twelfth transistor M12with a long channel length in order to obtain a negative temperature characteristic. The use of a MOSFET transistor with the long channel length is mean to overcome channel length modulation. That is, the use of the long channel length prevents a drain current of a transistor from changing when a drain-source voltage is changed. Accordingly, the drain current is not changed although a drain-source voltage is changed. The drain current is only changed by a signal inputted to a gate. In general, a current of a long channel transistor can be expressed as Eq. 6.

The current i3of the tenth transistor M10is equal to a current of the third resistor R3. The current i3is expressed as a value obtained by dividing the source voltage of the twelfth transistor M12by the third resistor R3.

A gate-source voltage VGSof the twelfth transistor M12is a difference between the gate voltage V3and a source voltage Vsof the twelfth transistor M12(VGS=V3−VS). Therefore, the current i3can be expressed as Eq. 7.

The source voltage Vscan be expressed as Eq. 8.

The source voltage Vsof the twelfth transistor M12has a negative temperature characteristic similar to the temperature characteristic of the voltage V3having a negative gradient. The current i3can be calculated based on Eq. 7 with the source voltage Vsexpressed in Eq. 8. That is, the current i3can be expressed as Eq. 9.

In Eq. 9, the current i3includes the component of V3of the second diode D2having a negative temperature characteristic. That is, the current i3has a negative temperature characteristic.

A threshold voltage VTHis defined as VTH0+γ(√{square root over (2ΦfVSB)}−√{square root over (2Φf)}). The threshold voltage VTHhas a very small temperature characteristic that can be ignored because it is small compared to the temperature characteristic of a voltage of a diode.

As a result, a current flowing through the fourteenth transistor M14is equal to the sum of i5and i4. Where is, the current i5flowing through the thirteenth transistor M13has a positive temperature characteristic, and the current i4flowing through the fourth resistor R4has a negative temperature characteristic. Therefore, the fourteenth transistor M14can generate a reference current less sensitive to temperature variation. The current iM14can be expressed as Eq. 10.

The current i4flowing into the eleventh transistor M11can be controlled using an area ratio of the tenth transistor M10and the eleventh transistor M11. In the present embodiment, the current ratio of the current of the tenth transistor M10and the current of the eleventh transistor M11is N:1. The fourth resistor R4is used to adjust a DC-voltage level.

The current iM14expressed in Eq. 10 can generate a stable reference current regardless of temperature variation through controlling a coefficient value. This current can be applied to circuits needed the reference current bias by being mirrored through the fourteenth transistor M14having a diode connection structure.

FIG. 3Ashows a gradient of a current according to a temperature.

As shown inFIG. 3A, the current i4has a negative gradient according to a temperature. The current i5has a positive gradient according to a temperature.

FIG. 3Bshows a reference current obtained by combining two currents ofFIG. 3A. The value of the reference current has a stable bias current characteristic less sensitive to temperature variation.

FIG. 2Bis a diagram illustrating a reference voltage bias circuit for a low supply voltage in accordance with another embodiment of the present invention. Compared to the reference current bias circuit shown inFIG. 2A, the reference voltage bias generating circuit according to the present embodiment includes a reference voltage generating block instead of the reference current mirroring unit250.

The reference voltage bias circuit according to the present embodiment includes the same constituent elements of the reference current bias circuit ofFIG. 2Bexcept a reference voltage providing unit350. Therefore, detail description of the same constituent elements is omitted. Hereinafter, the reference voltage providing unit350according to the present embodiment will be described.

InFIG. 2B, the reference voltage bias circuit includes a start-up circuit100, a bandgap reference voltage circuit300, and a reference current circuit400using a reference voltage thereof. The bandgap reference voltage circuit300has the same operation property of the bandgap reference current circuit200ofFIG. 2Aand the temperature compensated current flows through a fifth resistor R5. It generates a new voltage, that is, a reference voltage expressed as Eq. 11.

In Eq. 11, the reference voltage is lower than 1V and a stable voltage regardless of temperature variation by controlling a resistance value and a mirror current ratio.

FIG. 3Cis a graph showing relation between a temperature and the output voltage.

As shown, a reference voltage, which is generated for temperature compensation through controlling a coefficient, has a stable value that is less changed although a temperature is changed.

FIG. 3Dis a graph showing a value of a reference voltage that can be provided even in supply voltage variation lower than 1.5V.

As shown inFIG. 3D, a reference voltage is sustained at about 300 mV when a supply voltage VDD is higher than 0.9V.

As described above, the bias circuit for low supply voltage according to the present invention can generate a reference current and a reference voltage less sensitive to temperature variation. That is, the proposed reference bias circuit can provide a stable voltage and a stable current although a temperature is changed. Therefore, it is possible to reduce power consumption of total system.