A curvature compensation method and circuit immune to process variations

Abstract

The present invention discloses a curvature compensation method and circuit that are immune to process variations. This method primarily addresses the problem that existing curvature compensation technologies are susceptible to process variations and are unable to achieve immunity to these variations. This method divides the reference voltage in a reference circuit using resistors. The divided voltage is applied to the bases of two identically sized bipolar junction transistors forming a differential pair structure. The difference in collector currents of the two bipolar junction transistors is used to generate a compensation current with a nonlinear component, thereby offsetting the nonlinear component in the reference voltage. This method can be used not only in bandgap reference circuits but also in Zener reference circuits. Its curvature compensation effect is unaffected by process variations, and the magnitude and direction of the curvature compensation can be easily adjusted by the user.

Description

Technical Field

[0001] The present invention belongs to the technical field of reference source curvature compensation, and in particular relates to a curvature compensation method and circuit that are immune to process variations. Background Art

[0002] In the field of analog circuits, voltage references are widely used in high-precision systems such as analog-to-digital converters (ADCs) and low-dropout linear regulators (LDOs). In these applications, to meet the high-precision requirements of the system, a sufficiently low temperature coefficient of the reference voltage is generally desired.

[0003] Bandgap reference (BGR) and Zener reference are the most common types of reference voltage sources. The bandgap reference uses two BJT tubes with a fixed current density ratio. The difference between the base-emitter voltage drop ΔV BE With a positive temperature coefficient, the base-emitter voltage drop V BE It has a negative temperature coefficient. By adding a positive temperature coefficient voltage and a negative temperature coefficient voltage, a reference voltage with a temperature coefficient close to zero can be obtained. Unlike BGR, the Zener reference source generates a voltage drop V with a positive temperature coefficient through a Zener diode. ZN , and use the BJT tube's V BE The negative temperature coefficient of the reference voltage is compensated to achieve a reference voltage with zero temperature coefficient.

[0004] However, both the Zener diode voltage drop V ZN , or the V of the BJT tube BE , neither of which varies strictly linearly with temperature. Conventional bandgap and Zener reference circuits only compensate for the slope of the output voltage without considering higher-order nonlinearities. Consequently, the actual reference output voltage exhibits significant nonlinearity. Therefore, temperature coefficient curvature compensation technology is often employed to reduce the temperature coefficient. The principle behind this technology is to offset the inherent nonlinearity (curvature) in the circuit by introducing an additional nonlinear variable, thereby achieving a constant reference voltage output.

[0005] Furthermore, achieving an ultra-high-precision reference voltage (<0.5ppm / °C temperature coefficient) in a Zener reference circuit is often challenging. This is because, unlike a classic bandgap reference circuit, the curvature in a Zener reference circuit originates from the Zener transistor, not the BJT. Therefore, the classic curvature compensation techniques used in bandgap reference circuits cannot be applied to Zener references.

[0006] like Figure 1 As shown in the figure, a bandgap reference circuit of the prior art is provided. The circuit ensures that the resistor R 1A 、R 1BThe currents on the BJT tubes Q1 and Q2 are equal, thus ensuring that the currents on the BJT tubes Q1 and Q2 are equal. Since the area ratio of the BJT tubes Q1 and Q2 is 1:N, the difference between the base-emitter voltages V BE1 -V BE2 is a positive temperature coefficient voltage, and the base-emitter voltage V BE1 By adjusting the ratio of resistors R1, R2 and R3, the positive and negative temperature coefficients can be offset, thereby generating a reference voltage V with a zero temperature coefficient. BG .

[0007] The curvature compensation technology of existing solutions is as follows: Figure 2 By setting the reference voltage V BG Applied to the polysilicon resistor with a low temperature coefficient, a constant current I R At the same time, an additional BJT tube Q3 is introduced. Here, the area ratio of BJT tubes Q1 and Q3 is 1:M. The collector current flowing through BJT tube Q1 has a positive temperature coefficient, while the collector current I flowing through BJT tube Q3 R For BJT tube, the V generated by working under PTAT current and constant current is BE There are different nonlinear components. According to the analysis, by using the difference ΔV between the base-emitter voltage drop of BJT tubes Q1 and Q3 at different collector currents, BE , can achieve V BE The nonlinear component of curvature is compensated.

[0008] A disadvantage of this solution is that curvature compensation relies on the circuit structure of the bandgap reference circuit. This curvature compensation technology is only applicable to bandgap reference circuits and cannot be applied to Zener reference circuits. Therefore, the scope of application of the existing technical solution is relatively narrow.

[0009] In addition, the existing technical solution generates a constant current I R When applying the reference voltage to a specific polysilicon resistor, the resistance of the polysilicon resistor usually varies with the process, which also affects the curvature compensation accuracy. Summary of the Invention

[0010] The purpose of the present invention is to provide a curvature compensation method and circuit that are immune to process variations, mainly to solve the problem that the existing curvature compensation technology is affected by process variations and cannot be immune to process variations.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A curvature compensation method that is immune to process variations uses resistors to divide the reference voltage in a reference circuit. The divided voltage is applied to the bases of two bipolar junction transistors of the same size forming a differential pair structure. The difference in collector currents of the two bipolar junction transistors is used to form a compensation current with a nonlinear component, thereby offsetting the nonlinear component in the reference voltage.

[0013] Furthermore, in the present invention, by changing the base voltages applied to the two bipolar junction transistors, compensation currents of different compensation directions and arbitrary magnitudes can be obtained.

[0014] Based on the above curvature compensation method, the present invention also provides a curvature compensation circuit that is immune to process variations, including a bandgap reference circuit, a voltage divider resistor R7 and a resistor R8, one end of which is connected in series to the bandgap reference voltage output terminal of the bandgap reference circuit and the other end is grounded, and a nonlinear current generating circuit connected to both ends of the voltage divider resistor R7; the nonlinear current generating circuit is composed of two bipolar junction transistors Q with the same size and the emitter and collector connected to the same voltage divider resistor R7. X and Q Y The bipolar junction transistor Q X The base of the bipolar junction transistor Q is connected to one end of the voltage divider resistor R7. Y The base of the bipolar junction transistor Q is connected to the other end of the voltage divider resistor R7. X and Q Y The collector of the bipolar junction transistor Q is connected to the supply voltage VDD. X and Q Y The emitter tail current I PTAT Among them, I PTAT This is the PTAT current generated by the bandgap reference circuit itself.

[0015] Furthermore, in the present invention, the bandgap reference circuit includes an amplifier A1, a transistor Q4 connected to the inverting input terminal of the amplifier A1 after the emitter is grounded and the collector is connected to the base, a resistor R6 connected to the non-inverting input terminal of the amplifier A1, and a resistor R 5B , the emitter is grounded, the collector is connected to the base and then connected to the other end of the resistor R6, and one end is connected to the inverting input terminal of the amplifier A1. 5A , one end and the resistor R 5A The other end of the resistor R 5B The other end is connected to the resistor R A , and the drain and resistor R A The other end of the MOS transistor M1 is connected to the output end of the amplifier A1, the gate is connected to the output end of the amplifier A1, and the source is connected to the power supply voltage VDD; wherein the drain of the MOS transistor M1 is the bandgap reference voltage output end of the bandgap reference circuit.

[0016] Based on the above curvature compensation method, the present invention also provides another curvature compensation circuit that is immune to process variations, including a Zener reference circuit and a nonlinear current generating circuit connected to the Zener reference circuit for generating a differential compensation current; the nonlinear current generating circuit comprises two bipolar junction transistors Q with the same size and the emitter and collector connected to each other. X and Q Y The bipolar junction transistor Q X The base of the bipolar junction transistor Q is connected to one end of the voltage divider resistor in the Zener reference circuit. Y The base of the bipolar junction transistor Q is connected to the other end of the voltage divider resistor. X and Q Y The collector of the bipolar junction transistor Q is connected to the supply voltage VDD. X and Q Y The emitter tail current I PTAT Among them, I PTAT This is the PTAT current generated by the Zener reference circuit itself.

[0017] Furthermore, in the present invention, the Zener reference circuit includes an amplifier A2, a resistor R connected to the non-inverting input terminal of the amplifier A2 at one end. B , emitter and resistor R B a transistor Q6 connected to the other end of the transistor Q6, a transistor Q7 having a base connected to the output end of the amplifier A2 and an emitter connected to ground, a Zener diode Z1 having an anode connected to the non-inverting input end of the amplifier A2 and a cathode connected to the inverting input end of the amplifier A2, a current source G1 connected between the cathode of the Zener diode Z1 and the collector of the transistor Q6, a diode D3 having a cathode connected to the collector of the transistor Q7 and an anode connected to the collector of the transistor Q6, diodes D1 and D2 having a cathode connected to the collector of the transistor Q7 in series, a transistor Q8 having a base connected to the anode of the diodes D1 and D2 in series, a current source G2 having one end connected to the power supply voltage VDD and the other end connected to the base of the transistor Q8, a current source G3 having one end connected to the non-inverting input end of the amplifier A2 and the other end grounded, and resistors R9 and R1 connected in series with one end connected to the emitter of the transistor Q8 and the other end grounded. 10 、R 11 ; Among them, the base of transistor Q6 is connected to resistors R9, R 10 The common terminal of the transistor Q8 is connected to the power supply voltage VDD; the collector of the bipolar junction transistor Q X and Q Y The bases of the resistors R 10 The emitter of transistor Q8 serves as the output end of the Zener reference voltage.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention achieves reliable curvature compensation by using simple differential BJTs (bipolar junction transistors) with a fixed base voltage differential. It can be used not only in bandgap reference circuits but also in Zener reference circuits. Its curvature compensation effect is unaffected by process variations, and the user can easily adjust the magnitude and direction of the curvature compensation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a schematic diagram of a bandgap reference circuit in the prior art.

[0021] Figure 2 For Figure 1 Schematic diagram of the curvature compensation circuit of the bandgap reference circuit.

[0022] Figure 3 This is the nonlinear current generating circuit in the present invention.

[0023] Figure 4 For Figure 3 Schematic diagram of the nonlinear current changing with temperature.

[0024] Figure 5 Schematic diagram of a bandgap reference circuit in an embodiment of the present invention.

[0025] Figure 6 For Figure 5 Schematic diagram of the curvature compensation circuit of the bandgap reference circuit.

[0026] Figure 7 Schematic diagram of a Zener reference circuit in an embodiment of the present invention.

[0027] Figure 8 For Figure 7 Schematic diagram of the curvature compensation circuit of the Zener reference circuit. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings and examples. The embodiments of the present invention include but are not limited to the following examples.

[0029] like Figure 3As shown, the present invention discloses a curvature compensation method that is immune to process variations. The reference voltage in the reference circuit is divided using resistors. The divided voltage is applied to the bases of two identically sized bipolar junction transistors forming a differential pair structure. The difference in collector currents of the two bipolar junction transistors is used to generate a compensation current with a nonlinear component, thereby offsetting the nonlinear component in the reference voltage. Furthermore, the present invention can also obtain compensation currents of varying directions and arbitrary magnitudes by varying the base voltages applied to the two bipolar junction transistors.

[0030] Example 1

[0031] When the method is used in curvature compensation of a bandgap reference circuit, the curvature compensation circuit includes a bandgap reference circuit, a voltage divider resistor R7 and a resistor R8 connected in series, one end of which is connected to the bandgap reference voltage output terminal of the bandgap reference circuit and the other end is grounded, and a nonlinear current generating circuit connected to both ends of the voltage divider resistor R7, such as Figure 3 、 6 shown.

[0032] The nonlinear current generating circuit is composed of two bipolar junction transistors Q with the same size and the emitter and collector connected respectively. X and Q Y The bipolar junction transistor Q X The base of the bipolar junction transistor Q is connected to one end of the voltage divider resistor R7. Y The base of the bipolar junction transistor Q is connected to the other end of the voltage divider resistor R7. X and Q Y The collector of the bipolar junction transistor Q is connected to the supply voltage VDD. X and Q Y The emitter tail current I PTAT Among them, the tail current I PTAT is the PTAT current generated by the bandgap reference circuit itself. In addition, the voltage V X 、V Y The two voltages are obtained by dividing the reference voltage by resistors in the reference circuit, and are applied to two differential BJT (bipolar junction transistor) tubes Q of the same size. X , Q Y The base.

[0033] The bandgap reference circuit includes an amplifier A1, a transistor Q4 connected to the inverting input terminal of the amplifier A1 after the emitter is grounded and the collector is connected to the base, a resistor R6 connected to the non-inverting input terminal of the amplifier A1, and a resistor R 5B , the emitter is grounded, the collector is connected to the base and then connected to the other end of the resistor R6, and one end is connected to the inverting input terminal of the amplifier A1.5A , one end and the resistor R 5A The other end of the resistor R 5B The other end is connected to the resistor R A , and the drain and resistor R A The other end of the MOS transistor M1 is connected to the output end of the amplifier A1, the gate is connected to the output end of the amplifier A1, and the source is connected to the power supply voltage VDD; wherein the drain of the MOS transistor M1 is the bandgap reference voltage output end of the bandgap reference circuit.

[0034] like Figure 3 As shown, due to the BJT tube Q X , Q Y The base-emitter voltage difference is different, so the collector current flowing through the left and right branches is different. The following shows two commonly used formulas for BJT tubes, one for IV relationship and the other for transconductance:

[0035]

[0036] g m =I C / V T (2)

[0037] Among them, V BE is the base-emitter voltage, V T is the thermal voltage, I S is the saturation current, I C is the collector current, g m is the transconductance. In addition, according to the definition of transconductance, the difference between the currents of the left and right branches can be expressed as follows:

[0038] I X -I Y =g my (V X -V Y ) (3)

[0039] Among them, I X , I Y Flow through Q X , Q Y Collector current, g mY is the transistor Q Y At the same time, by Figure 3 It can be seen that the tail current I PTAT It can be expressed as:

[0040] I PTAT =I X +I Y (4)

[0041] Combining equations (2), (3) and (4), we can obtain:

[0042]

[0043]

[0044] Where ΔI is the difference between the currents of the two branches. In formula (6), V X -V Y is a constant voltage (because it is a voltage divider of the reference voltage), and I PTAT V changes linearly with temperature, so the entire numerator changes linearly with temperature. In addition, in the denominator, V X -V Y is a constant voltage, V T It increases linearly with temperature. Therefore, at high temperatures, the denominator increases, which causes the entire ΔI to decrease, thus introducing a nonlinear component to ΔI. Figure 4 The curve of ΔI changing with temperature is shown. It can be seen that ΔI has a nonlinear component, which can be used to offset the nonlinearity in the reference voltage.

[0045] In addition, if you need to adjust the curvature of ΔI, you can change V X -V y Since V X -V Y It is obtained by dividing the reference voltage. By changing the voltage division ratio, V X -V Y value.

[0046] also, Figure 4 The curve in is convex, not concave. If a concave curve is desired, it can be achieved by changing the direction of the current difference. Specifically, ΔI can be redefined as ΔI = I Y -I X , rather than the previous ΔI=I X -I Y , which changes the concavity and convexity of the ΔI curvature.

[0047] Another benefit of the present invention is that the curvature compensation technology proposed is not affected by process variations, that is, ΔI·R is not affected by process variations. Specifically, in equation (6), the value of ΔI depends on V X -V Y The value of V T The value of I PTAT The value of V X -V Y It is obtained by dividing the reference voltage. Since the reference voltage (after correction) is not affected by process changes, V X -V Y The value of is also not affected by process variations. In addition, the V Tis the thermal voltage, which is process independent and therefore not affected by process variations. The only voltage that is affected by process variations is I PTAT This is because I PTAT Usually ΔV BE / R, which is similar to the I PTAT The current generation mechanism. Fortunately, after multiplying by the resistance R, the obtained I PTAT ·R(=ΔV BE ) is a quantity that is independent of process variations because ΔV BE Proportional to the thermal voltage V T In short, the curvature compensation technology of the present invention is not affected by process changes and has obvious advantages over traditional technologies.

[0048] exist Figure 6 middle, I PTAT1 represents the PTAT current generated by the bandgap reference itself, and ΔI represents the differential current generated by the curvature compensation circuit in this embodiment. Before the introduction of curvature compensation technology, the bandgap reference voltage V BG It can be expressed as (see Figure 5 ):

[0049] V BG =V1+I PTAT1 R A (7)

[0050] In contrast, after the introduction of curvature compensation technology, the bandgap reference voltage V BG It can be expressed as (see Figure 6 ):

[0051] V BG =V1+(I PTAT1 +ΔI)R A (8)

[0052] Since the newly added ΔI·R A It has nonlinear components and can therefore be used to offset the reference voltage V BG Nonlinearity in .

[0053] Example 2

[0054] When the method is used in the curvature compensation of the Zener reference circuit, the curvature compensation circuit includes the Zener reference circuit and a nonlinear current generating circuit connected to the Zener reference circuit for generating a differential compensation current; the nonlinear current generating circuit is composed of two bipolar junction transistors Q with the same size and the emitter and collector connected to each other. X and Q Y The bipolar junction transistor Q XThe base of the bipolar junction transistor Q is connected to one end of the voltage divider resistor in the Zener reference circuit. Y The base of the bipolar junction transistor Q is connected to the other end of the voltage divider resistor. X and Q Y The collector of the bipolar junction transistor Q is connected to the supply voltage VDD. X and Q Y The emitter tail current I PTAT Among them, I PTAT This is the PTAT current generated by the Zener reference circuit itself.

[0055] The Zener reference circuit includes an amplifier A2, a resistor R connected to the positive input terminal of the amplifier A2, and a resistor R connected to the positive input terminal of the amplifier A2. B , emitter and resistor R B a transistor Q6 connected to the other end of the transistor Q6, a transistor Q7 having a base connected to the output end of the amplifier A2 and an emitter connected to ground, a Zener diode Z1 having an anode connected to the non-inverting input end of the amplifier A2 and a cathode connected to the inverting input end of the amplifier A2, a current source G1 connected between the cathode of the Zener diode Z1 and the collector of the transistor Q6, a diode D3 having a cathode connected to the collector of the transistor Q7 and an anode connected to the collector of the transistor Q6, diodes D1 and D2 having a cathode connected to the collector of the transistor Q7 in series, a transistor Q8 having a base connected to the anode of the diodes D1 and D2 in series, a current source G2 having one end connected to the power supply voltage VDD and the other end connected to the base of the transistor Q8, a current source G3 having one end connected to the non-inverting input end of the amplifier A2 and the other end grounded, and resistors R9 and R1 connected in series with one end connected to the emitter of the transistor Q8 and the other end grounded. 10 、R 11 ; Among them, the base of transistor Q6 is connected to resistors R9, R 10 The common terminal of the transistor Q8 is connected to the power supply voltage VDD; the collector of the bipolar junction transistor Q X and Q Y The bases of the resistors R 10 The emitter of transistor Q8 serves as the output end of the Zener reference voltage.

[0056] like Figure 3 、 8 As shown, in the curvature compensation of the Zener reference circuit, I PTAT2 represents the PTAT current generated by the Zener reference itself, and ΔI represents the differential current generated by the curvature compensation circuit in this embodiment. ZN It represents the conduction voltage drop of the Zener diode in the conduction state. Due to the clamping effect of amplifier A2, the node voltage V2 and the node voltage V ZN The base-emitter voltage VBE6 V ZN Before the introduction of this patented curvature compensation technology, the Zener reference voltage V OUT It can be expressed as (see Figure 7 ):

[0057]

[0058] In contrast, after the introduction of the patented curvature compensation technology, the Zener reference voltage V OUT It can be expressed as (see Figure 8 ):

[0059]

[0060] Since the newly added ΔI·R B It has nonlinear components and can therefore be used to offset the reference voltage V OUT Nonlinearity in .

[0061] In summary, the curvature compensation circuit of the present invention is simple, reliable, and unaffected by process variations. The user can freely adjust the magnitude and direction of curvature compensation. It can be used not only in bandgap reference circuits but also in Zener reference circuits. Compared with the prior art, the present invention offers outstanding substantive features and significant advancements.

[0062] The above embodiment is only one of the preferred implementation methods of the present invention and should not be used to limit the scope of protection of the present invention. Any changes or modifications that have no substantive meaning made to the main design concept and spirit of the present invention, as long as the technical problems solved are still consistent with the present invention, should be included in the scope of protection of the present invention.

Claims

1. A curvature compensation circuit that is immune to process variations, characterized in that: It includes a bandgap reference circuit, a voltage divider resistor connected in series with one end connected to the bandgap reference voltage output end of the bandgap reference circuit and the other end grounded. R 7. Resistors R 8, and connected to the voltage divider resistor R 7. A nonlinear current generating circuit at both ends of the circuit; the nonlinear current generating circuit is composed of two bipolar junction transistors of the same size with emitters and collectors connected correspondingly. Q X and Q Y constitute, Among them, bipolar junction transistor Q X The base and the voltage divider resistor R One end of 7 is connected to the bipolar junction transistor Q Y The base and the voltage divider resistor R The other end of 7 is connected to the bipolar junction transistor Q X and Q Y The collector of the bipolar junction transistor is connected to the supply voltage VDD. Q X and Q Y The emitter tail current I PTAT ;in, I PTAT The PTAT current is generated by the bandgap reference circuit itself. The curvature compensation method of the curvature compensation circuit is as follows: the reference voltage in the bandgap reference circuit is divided by a voltage-dividing resistor, the divided voltage is applied to the bases of two bipolar junction transistors of the same size forming a differential pair structure, and the difference between the collector currents of the two bipolar junction transistors is used to form a compensation current with a nonlinear component, thereby offsetting the nonlinear component in the reference voltage. Moreover, by changing the base voltage applied to the two bipolar junction transistors, compensation currents of different compensation directions and arbitrary sizes can be obtained.

2. The curvature compensation circuit immune to process variations according to claim 1, characterized in that: The bandgap reference circuit includes an amplifier A 1. The emitter is grounded, the collector is connected to the base and then connected to the amplifier A 1's inverting input is connected to the transistor Q 4. One end and the amplifier A 1 is connected to the non-inverting input of the resistor R 6 and resistor R 5B , the emitter is grounded, the collector is connected to the base and then connected to the resistor R The other end of 6 is connected to the transistor Q 5. One end and the amplifier A 1 is connected to the inverting input of the resistor R 5A , one end and the resistor R 5A The other end of the resistor R 5B The other end of the resistor is connected to R A , and the drain and resistor R A The other end of the gate is connected to the amplifier A 1's output terminal is connected to the MOS tube whose source terminal is connected to the power supply voltage VDD M 1; Among them, MOS tube M The drain of 1 is the bandgap reference voltage output terminal of the bandgap reference circuit.

3. A curvature compensation circuit that is immune to process variations, characterized in that: The invention comprises a Zener reference circuit and a nonlinear current generating circuit connected to the Zener reference circuit for generating a differential compensation current; the nonlinear current generating circuit comprises two bipolar junction transistors of the same size with emitters and collectors connected correspondingly. Q X and Q Y constitute, Among them, bipolar junction transistor Q X The base of the bipolar junction transistor is connected to one end of the voltage divider resistor in the Zener reference circuit. Q Y The base of the bipolar junction transistor is connected to the other end of the voltage divider resistor. Q X and Q Y The collector of the bipolar junction transistor is connected to the supply voltage VDD. Q X and Q Y The emitter tail current I PTAT ;in, I PTAT The PTAT current is generated by the Zener reference circuit itself. The curvature compensation method of the curvature compensation circuit is as follows: the reference voltage in the Zener reference circuit is divided by a voltage-dividing resistor, the divided voltage is applied to the bases of two bipolar junction transistors of the same size forming a differential pair structure, and the difference between the collector currents of the two bipolar junction transistors is used to form a compensation current with a nonlinear component, thereby offsetting the nonlinear component in the reference voltage. By changing the base voltage applied to the two bipolar junction transistors, compensation currents of different compensation directions and arbitrary sizes can be obtained.

4. The curvature compensation circuit immune to process variations according to claim 3, characterized in that: The Zener reference circuit includes an amplifier A 2. One end and the amplifier A 2. The non-inverting input terminal is connected to a resistor R B , emitter and resistor R B The other end of the transistor is connected to Q 6. Base and amplifier A 2 output terminals connected to the transistor with the emitter grounded Q 7. The positive pole is grounded and the negative pole is connected to the amplifier A 2. The inverting input terminal is connected to a Zener diode Z 1. Connect to Zener diode Z The negative electrode of 1 and the transistor Q 6. Current source between the collectors G 1. Negative electrode and transistor Q The collector of 7 is connected to the positive electrode of the transistor Q 6. The collector of the diode is connected to D 3. After connecting the negative electrode in series with the transistor Q 7. The collector of the diode is connected to D 1. D 2. Base and series connected diode D 1. D 2's positive pole is connected to the transistor Q 8. One end is connected to the power supply voltage VDD and the other end is connected to the transistor Q 8 The base is connected to a current source G 2. One end is connected to the amplifier A 2 non-inverting input terminal and the other end of the current source grounded G 3, and one end connected in series with the transistor Q The emitter of 8 is connected to the resistor with the other end grounded R 9. R 10 、 R 11 ; Among them, the transistor Q The base of 6 is connected to the resistor R 9. R 10 The common terminal of the transistor Q The collector of 8 is connected to the supply voltage VDD; the bipolar junction transistor Q X and Q Y The bases of the resistors R 10 The two ends of the transistor Q The emitter of 8 serves as the output terminal of the Zener reference voltage.

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