TWI385500B - Bandgap reference voltage generator for low supply voltage - Google Patents

Description

Low-supply voltage bandgap reference voltage generator

The present invention relates to a bandgap reference voltage generator, and more particularly to a bandgap reference voltage generator of low supply voltage.

1 is a conventional bandgap reference voltage generator, including a current source 10 providing a current I _PTAT having a positive temperature coefficient, a current source 12 providing a bias current I _BIAS , a transistor P2 having an emitter connected current source 12, and a resistor R22 Connected between the emitter and the base of the transistor P2, the resistor R23 is connected between the base of the transistor P2 and the ground GND, and the buffer 14 is connected to the base of the transistor P2. The buffer 14 buffers the reference voltage Vref, which includes an operational amplifier 16 connected to a voltage follower having a positive input coupled to the base of the transistor P2 and a negative input coupled to its output. This bandgap reference generator provides a reference voltage

Vref=I _R23 ×R23, Equation 1

The current I _{R23 of the} resistor R23 is equal to the sum of the current I _PTAT and the current I _PTVBE . Current I _PTVBE = Vbe1/R22, Vbe1 is the emitter-base voltage of transistor P2, with a negative temperature coefficient, Equation 1 can be rewritten as

Vref = (I _PTAT + Vbe1/R22) × R23. Formula 2

2 is the current source 10 of FIG. 1, wherein the transistors M1 and M2 are respectively connected between the power supply terminal Vcc and the positive and negative inputs of the operational amplifier 20, and the output of the operational amplifier 20 is connected to the gates of the transistors M1 and M2. The resistor R0 is connected in series with the transistor Q1 between the positive input of the operational amplifier 20 and the ground GND. The transistor Q2 is connected between the negative input of the operational amplifier 20 and the ground GND, and the transistors Q1 and Q2 are connected to the diode. The size ratio of the two is N:1, the transistor M6 and the transistor M1 form a current mirror, and the current I1 that is mirrored through the transistor M1 generates a current I _PTAT , and the starting circuit 22 is used to activate the current source 10 . In the startup circuit 22, the transistor M3 is connected between the power supply terminal Vcc and the negative input of the operational amplifier 20, and the transistor M4 is connected between the power supply terminal Vcc and the gate of the transistor M3, and forms a current mirror with the transistor M1. The transistor M5 is connected between the gate of the transistor M3 and the ground GND, and its gate is connected to the power supply terminal Vcc.

When the power source voltage Vcc is applied to start the current source 10, the transistors M3 and M5 are turned on, the transistor M5 is equivalent to the resistor, and the negative input of the operational amplifier 20 is connected to the power supply terminal Vcc via the transistor M3, so that the voltage of the negative input of the operational amplifier 20 rises. The output of the operational amplifier 20 is thus lowered, which in turn conducts the crystal M1 to generate the current I1, and the transistor M4 mirrors the current I1 to generate the current I3, causing the gate voltage of the transistor M3 to rise. After the gate voltage of the transistor M3 rises to a certain threshold, the transistor M3 turns off, thereby turning off the startup circuit 22, and the current source 10 is started.

When the current source 10 is in a steady state, the operational amplifier 20 maintains the voltages of its two inputs equal, the transistors M1 and M6 have the same size, and the transistors Q1 and Q2 have a size ratio N:1, so the current

I _PTAT =I1=[VT×ln(N)]/R0, Equation 3

Where VT is a thermal voltage with a positive temperature coefficient. Substituting formula 3 into formula 2 can be obtained

Vref={[VT×ln(N)]/R0+Vbe1/R22}×R23=R23/R22×[Vbe1+VT×ln(N)×R22/R0]. Formula 4

It can be known from Equation 4 that adjusting the value of R22/R0 can make the temperature coefficient of the reference voltage Vref be 0, but the reference voltage Vref can be made only when [Vbe1+VT×ln(N)×R22/R0] is about 1.24V. The temperature coefficient is zero. Adjust the value of R23/R22 to adjust the value of the reference voltage Vref.

However, the bandgap reference voltage generator of FIG. 1 can adjust the reference voltage Vref to be lower than 1 V, but cannot be driven with a power supply voltage Vcc lower than 1 V. For example, if the reference voltage Vref=0.8V, the voltage on the emitter of the transistor R2 will be 0.8V+Vbe1, so the power supply voltage Vcc must be greater than 0.8V+Vbe1, and Vbe1 is about 0.5V~0.7V, so The power supply voltage Vcc must not be lower than 1V. Furthermore, the transistor P2 will generate the base current Ib through the resistor R23, and the greater the base current Ib, the greater the influence on the reference voltage Vref. According to the current formula of the bipolar junction transistor, the base current of the transistor P2

Ib=Ic/β, Equation 5

Where Ic is the collector current of the transistor P2 and β is the current gain of the transistor P2. Therefore, the bandgap reference voltage generator of FIG. 1 is susceptible to the current gain β of the transistor P2.

Therefore, a bandgap reference voltage generator having a low power supply voltage and being unaffected by the current gain β of the transistor P2 is what it is.

One of the objects of the present invention is to provide a bandgap reference voltage generator with a low supply voltage.

One of the objects of the present invention is to provide a bandgap reference voltage generator that is unaffected by the current gain of the transistor.

According to the present invention, a bandgap reference voltage generator for providing a reference voltage includes a T-type resistor network connecting two current sources and a transistor, the two current sources respectively providing a current having a positive temperature coefficient and a bias current, The T-type resistor network determines the temperature coefficient of the reference voltage. The reference voltage is taken from the T-type resistor network

The power supply voltage of the bandgap reference voltage generator and the reference voltage differ only in the voltage across the first current source. Since the current source cross-voltage can be small, the bandgap reference voltage generator requires only a very low supply voltage. In addition, the base of the transistor is grounded, so its base current flows to the ground, so its current gain does not affect the reference voltage.

3 is an embodiment of the present invention, in addition to the current sources 10 and 12, the transistor P2, and the buffer 14 of FIG. 1, a T-type network composed of resistors R1, R2, and R3. In the bandgap reference voltage generator, the emitter of the transistor P2 is connected to the current source 12, the collector and the base are grounded, the first terminal 30 of the resistor R1 is connected to the current source 10, and the resistor R2 is connected to the transistor P2. Between the pole and the second end 32 of the resistor R1, the resistor R3 is connected between the second end 32 of the resistor R1 and the base of the transistor P2, and the buffer 14 is connected to the first end 30 of the resistor R1 to buffer the reference of the supply. The voltage Vref, the buffer 14 also has an operational amplifier 16 connected to a voltage follower. The current source 10 provides a current I _PTAT having a positive temperature coefficient to the resistors R1 and R3, and the resistors R2 and R3 connected between the emitter and the base of the transistor P2 are negatively generated according to the emitter-base voltage Vbe1 of the transistor P2. Temperature coefficient current

I _PTVBE = Vbe1/(R2+R3). Formula 6

The reference voltage Vref is equal to the sum of the voltages of the resistors R1 and R3, so the reference voltage

Vref = I _PTAT × (R1 + R3) + I _PTVBE × R3. Formula 7

Substituting Equation 3 and Equation 6 into Equation 7

Vref=[R3/(R2+R3)]×{Vbe1+VT×ln(N)×[(R1+R3)/R0]×[(R2+R3)/R3]}, Equation 8

Therefore, adjusting the value of [(R1+R3)/R0]×[(R2+R3)/R3] can make the temperature coefficient of the reference voltage Vref 0, and adjust the value of R3/(R2+R3) to adjust the reference voltage Vref. Value.

The bandgap reference voltage generator of FIG. 3 draws the reference voltage Vref from the first terminal 30 of the resistor R1 instead of the base of the transistor P2, so that the power supply voltage Vcc is greater than the sum of the voltage across the reference voltage Vref and the current source 10 The bandgap reference voltage generator can be driven, and the voltage across the current source 10 is very small, about 0.1V, so when the reference voltage Vref=0.8V, the power supply voltage Vcc is sufficient as long as 0.9V, so the energy gap of FIG. The reference voltage generator can still operate at a low supply voltage Vcc. The base of the transistor P2 is grounded, so the base current Ib flows to the ground GND without affecting the reference voltage Vref, that is, the bandgap reference voltage generator is not affected by the current gain β of the transistor P2. The voltage of an alkaline battery is about 0.9V~1.6V. If the reference voltage Vref=0.8V provided by the bandgap reference voltage generator in Figure 3, and the power supply voltage Vcc is provided by an alkaline battery, then the energy gap reference The voltage generator's reference voltage Vref can be generated directly from an alkaline battery.

10. . . Battery

12. . . Battery

14. . . buffer

16. . . Operational Amplifier

20. . . Operational Amplifier

twenty two. . . Startup circuit

30. . . First end of resistor R1

32. . . Second end of resistor R1

Figure 1 is a conventional bandgap reference voltage generator;

Figure 2 is a current source providing a positive temperature coefficient current in Figure 1;

Figure 3 is an embodiment of the invention.

10. . . Battery

12. . . Battery

14. . . buffer

16. . . Operational Amplifier

30. . . First end of resistor R1

32. . . Second end of resistor R1

Claims (8)

A low-supply voltage bandgap reference voltage generator for providing a reference voltage, comprising: a first resistor having a first end and a second end, the first end supplying the reference voltage; the first current source being connected to the power source Providing a current having a positive temperature coefficient between the terminal and the first end of the first resistor; a transistor having an emitter, a collector and a base; and a second current source connected to the power terminal and the transistor Between the poles, a bias current is provided; a second resistor is coupled between the emitter of the transistor and the second end of the first resistor; and a third resistor coupled to the second end of the first resistor and the Between the bases of the transistor. The energy gap reference voltage generator of claim 1, further comprising a buffer connected to the first end of the first resistor to buffer the reference voltage. A gapped reference voltage generator as claimed in claim 2, wherein the buffer comprises an operational amplifier connected to a voltage follower. The gap reference voltage generator of claim 1, wherein the reference voltage is equal to a sum of voltages of the first and third resistors. The energy gap reference voltage generator of claim 1, wherein the resistance values of the second and third resistors determine the magnitude of the reference voltage. The gap reference voltage generator of claim 1, wherein the resistance values of the first, second, and third resistors determine a temperature coefficient of the reference voltage. The gapped reference voltage generator of claim 1, wherein the first, second, and third resistors form a T-type network. A gapped reference voltage generator as claimed in claim 1, wherein the base of the transistor is grounded.