CN119396245B - Zero temperature coefficient reference circuit - Google Patents

Abstract

A zero temperature coefficient reference circuit is a reference circuit of a 2.5V reference source composed of a triode and a resistor, the reference circuit includes a bias circuit and a reference core circuit, and a current source VIN generates a bias current through the bias circuit to power the reference core circuit. The invention provides a new 2.5V reference circuit, which can achieve the stability of the reference by using a simple loop, does not require a compensation circuit, has a simple circuit structure, a clear principle, and is easy to implement. Through a small-scale circuit structure, a 2.5V reference with a zero temperature coefficient can be achieved, which saves chip area and reduces costs.

Description

Zero temperature coefficient reference circuit

Technical Field

The invention belongs to the technical field of integrated circuits, relates to power management of integrated circuits, in particular to a band gap reference technology, and provides a zero temperature coefficient reference circuit.

Background

The conventional bandgap reference is 1.25V, but some industrial applications use a 2.5V reference source, and therefore, a double bandgap reference voltage is used, and an operational amplifier circuit is used to realize a double reference, which needs to consider the problem of loop stability. Because the system circuit of the double band gap reference voltage is complex, the area of the reference chip is large, and the cost is high. For example, fig. 1 shows a conventional 2.5V reference circuit, with a voltage at the REF terminal of 2.5V. Two compensation capacitors are needed in the circuit for loop stabilization, namely an output miller compensation A of the first stage of the operational amplifier and a compensation capacitor B of the input end of the Darlington tube to CATHODE. Since the capacitance in bipolar technology is generally small in square value, the two capacitors occupy about half of the total chip area.

Disclosure of Invention

The invention aims to solve the technical problems that an additional compensation circuit is needed in the design of a reference source of 2.5V of the existing band gap reference circuit, the circuit is complex, and the circuit area is large.

The reference circuit with zero temperature coefficient comprises a reference circuit of a 2.5V reference source composed of a triode and a resistor, wherein the reference circuit comprises a bias circuit and a reference core circuit, a current source VIN generates bias current through the bias circuit to supply power for the reference core circuit, the reference core circuit comprises PNP transistors p1-p7, resistors R1-R9 and an NPN tube n1, and the reference core circuit comprises the following components:

The bias current output is respectively grounded through R1 and p1, grounded through p2, R2 and R3, grounded through R4 and p3, grounded through R5, p4 and R6, grounded through p5, R7 and p6, grounded through p7 and R8 and grounded through n1, wherein the base of p1 is connected between R2 and R3, the base of p2 is connected between R1 and p1, the base of p3 is connected between p2 and R2, the base of p4 is connected between R4 and p3, the base of p5 is connected with p5 collector, the base of p6 is connected between p4 and R6, the base of p7 is connected between R7 and p6, and the base of n1 is connected between p7 and R8;

The output end of the bias circuit is a reference voltage, n1 is used for pulling down a bias circuit current source to form stable reference output, R1, R2, R3, p1 and p2 are used for setting temperature coefficients of the reference circuit, negative temperature coefficient currents related to Vbe of the p1 and the p2 are realized by adjusting resistance ratio of the R1, R2 and R3, p3, R4, R5 and R6 are used for realizing positive temperature coefficients related to DeltaVbe and are used for level shift, the reference voltage is raised and used for controlling a driving pole, and p5, p6, p7, R7 and R8 are used as driving poles together and used for controlling output of n 1.

Further, the bias circuit comprises PNP pipes p8-p10, a resistor R9 and NPN pipes n2, the p8 and p9 emitters are connected with VIN, the bases are connected with each other, the base of the p9 is also connected with a p9 collector and a p10 emitter, the collector of the p8 is connected with the base of the p10 and the collector of the n2, the collector of the p10 is connected with the base of the n2, the collector output of the p10 is simultaneously a reference output Vref=2.5V, and the emitter of the n2 is grounded through the R9;

The p8 and p9 mirror current sources VIN, p10 are used as negative feedback ends to realize the matching of p8 and p9 currents, and n2 and R9 are used for setting the bias currents of p8 and p9, and the current value is (Vref-Vbe_n2)/R9.

The invention provides a novel 2.5V reference technology, which can realize the stability of the reference by adopting a simple loop, does not need a compensation circuit, has a simple circuit structure, clear principle and is easy to realize. Meanwhile, the invention can realize the reference of 2.5V with zero temperature coefficient through a small-scale circuit structure, thereby saving the chip area and reducing the cost.

Drawings

Fig. 1 is a circuit schematic diagram of a 2.5V reference circuit in the prior art.

Fig. 2 is a circuit schematic of a zero temperature coefficient 2.5V reference circuit of the present invention.

Fig. 3 is a circuit simulation effect diagram of an embodiment of the present invention.

Detailed Description

The practice of the invention is described in detail below with reference to fig. 2.

The reference circuit comprises a reference circuit of a 2.5V reference source composed of triodes and resistors, wherein the reference circuit comprises a bias circuit and a reference core circuit, a current source VIN generates bias current through the bias circuit to supply power for the reference core circuit, the reference core circuit comprises PNP tubes p1-p7, resistors R1-R9 and an NPN tube n1, and the bias circuit comprises PNP tubes p8-p10, a resistor R9 and an NPN tube n2.

The reference core circuit is as follows:

The bias current output is respectively grounded through R1 and p1, grounded through p2, R2 and R3, grounded through R4 and p3, grounded through R5, p4 and R6, grounded through p5, R7 and p6, grounded through p7 and R8, and grounded through n1, namely the output of the bias circuit is respectively grounded through 7 paths, wherein the base of p1 is connected between R2 and R3, the base of p2 is connected between R1 and p1, the base of p3 is connected between p2 and R2, the base of p4 is connected between R4 and p3, the base of p5 is connected with p5 collector, the base of p6 is connected between p4 and R6, the base of p7 is connected between R7 and p6, and the base of n1 is connected between p7 and R8.

The bias circuit is as follows:

in the bias circuit, p8 and p9 emitters are connected with VIN, bases are connected with each other, a p9 collector and a p10 emitter are also connected with the base of p8, the collector of p8 is connected with the base of p10 and the collector of n2, the collector of p10 is connected with the base of n2, the collector output of p10 is reference output Vref=2.5V, and the emitter of n2 is grounded through R9.

The output end of the bias circuit is reference voltage, namely collector outputs Vref of p10, p8 and p9 mirror current sources VIN, p10 are used as negative feedback ends, matching of p8 and p9 currents is achieved, n2 and R9 are used for setting bias currents of p8 and p9, the current value is (Vref-Vbe_n2)/R9, and Vbe_n2 represents Vbe of n 2. n1 is used to pull down the current source of p10 to form a stable reference output vref=2.5v. R1, R2, R3, p1 and p2 are used for setting temperature coefficients, and negative temperature coefficient currents related to Vbe of the p1 and the p2 are realized by adjusting the resistance ratio of the R1, the R2 and the R3. p3, p4, R5, R6 are used to achieve a positive temperature coefficient related to avbe, and are used for level shifting, and the reference voltage is raised for controlling the drive pole. p5, p6, p7, and R7, R8 are commonly used as the drive poles for controlling the output of n 1. The p5 base electrode and the collector electrode are connected, so that micro-conduction of p7 is facilitated, and oscillation caused by complete turn-off of n1 is avoided.

The circuit of the present invention achieves a zero temperature coefficient 2.5V reference, as illustrated by the example analysis below.

In this embodiment, the PNP transistor size of the reference core circuit is the same, assuming that R is a unit resistance value, r1=7xr, r2=0.25×r, r3=6.5×r, r4=70xr, r5=6xr, r6=84×r, r7=23xr, r8=12xr is set, among the 7 paths of the reference core circuit, let the path current corresponding to R1 be I1, the path current corresponding to p2 be I2, the path current corresponding to R4 be I3, and the path current corresponding to R5 be I4, i1=i2, i3=i4 can be implemented, and i1=10xi3 is adopted, and i3=i is the unit current value, so that Vbe of p1 and p2 is equal, and Vbe of p3 and p4 is equal, thereby simplifying the calculation.

According to the reference circuit of the present invention, there is:

Vref=Vbe_p2+Vbe_p1+I2*R3= Vbe_p3+Vbe_p4+I4*R5+ I2*(R2+R3)

can obtain 2 x delta Vbe =vbe_p2+ Vbe_p1- (Vbe_p3+ Vbe_p4) Vbe/u p 4)

For a PNP transistor, vbe=vt×ln (Ic/Is) Is obtained from ic=is×exp (Vbe/VT), ic Is the emitter-to-collector current, and Is the saturation current. T=kt/q is the thermal voltage, k is the b boltzmann constant, q is the electron charge amount, T is the temperature in kelvin, and VT and temperature T are proportional. Vbe is the base-emitter voltage.

Thus there is

2*ΔVbe= Vbe_p2+Vbe_p1-(Vbe_p3+Vbe_p4)

=VT* ln(Ic_p2/Is)+ VT* ln(Ic_p1/Is)- VT* ln(Ic_p3/Is)- VT* ln(Ic_p4/Is)

= VT* ln[Ic_p2* Ic_p1/( Ic_p3* Ic_p4)]

= VT* ln100=4.6*VT;

It is possible to obtain avbe=2.3×vt, i.e. avbe and VT and temperature T are proportional.

Combining the above formulas, one can get: 2 x avbe=4.6 x vt= i2+r2+. I4×r5

I.e., avbe is a positive temperature coefficient, while the product of the unit current I and the unit resistance r and VT are correlated, exhibiting a positive temperature coefficient.

According to the square value of the circuit, namely the resistance value of the resistor based on the unit resistor, the following can be obtained:

I2*R2+ I4*R5=10*I*0.25r+I*6R=8.5*I*r

reduced i×r=4.6×vt/8.5.

Since both I R and VT are proportional to avbe, there is a positive temperature coefficient, combined with a negative temperature coefficient for Vbe, a zero temperature coefficient, e.g., constant α, can be achieved with I2R 3 being proportional to avbe by a constant.

Vref=Vbe_p2+Vbe_p1+α*ΔVbe=Vbe_p2+Vbe_p1+I2*R3,

The appropriate resistance is set such that i2×r3=65×ir, approximately equal to 34.4×vt.

Theoretically, the temperature coefficient of VT is about 0.087 mV/o K, and the temperature coefficient of Vbe is about-1.5 mV/o K, and the temperature coefficient when vref=vbe+17.2vt is approximately zero can be obtained from the textbook.

Corresponding to the reference circuit:

Vref=Vbe_p2+Vbe_p1+α*ΔVbe =Vbe_p2+Vbe_p1+I2*R3= Vbe_p2+Vbe_p1+34.4*VT

the zero temperature coefficient reference value vref=2.5v of the reference circuit theory of the present invention can be obtained.

By combining the above, the invention can realize the reference voltage of Vref=2.5V with zero temperature coefficient by adopting a simple circuit, does not need a compensation circuit and a capacitor, and can obviously reduce the chip area.

The circuit of fig. 2 is simulated under the condition that when the power supply vdd=5v is used for scanning the temperature characteristic, the simulation result is shown in fig. 3, the temperature t= -40 to 180 degrees, the Vref is changed by 37mV, the corresponding temperature coefficient is about 1.5%, the design requirement is met, and the circuit of the invention can effectively realize the effect of zero temperature coefficient reference.

Claims (3)

1. The reference circuit is characterized by comprising a reference circuit of a 2.5V reference source composed of a triode and a resistor, wherein the reference circuit comprises a bias circuit and a reference core circuit, a current source VIN generates bias current through the bias circuit to supply power for the reference core circuit, the reference core circuit comprises PNP transistors p1-p7, resistors R1-R9 and an NPN tube n1, and the reference core circuit comprises the following components:

The bias current output is respectively grounded through R1 and p1, grounded through p2, R2 and R3, grounded through R4 and p3, grounded through R5, p4 and R6, grounded through p5, R7 and p6, grounded through p7 and R8 and grounded through n1, wherein the base of p1 is connected between R2 and R3, the base of p2 is connected between R1 and p1, the base of p3 is connected between p2 and R2, the base of p4 is connected between R4 and p3, the base of p5 is connected with p5 collector, the base of p6 is connected between p4 and R6, the base of p7 is connected between R7 and p6, and the base of n1 is connected between p7 and R8;

The output end of the bias circuit is a reference voltage, n1 is used for pulling down a bias circuit current source to form stable reference output, R1, R2, R3, p1 and p2 are used for setting temperature coefficients of the reference circuit, negative temperature coefficient currents related to Vbe of the p1 and the p2 are realized by adjusting resistance ratio of the R1, R2 and R3, p3, R4, R5 and R6 are used for realizing positive temperature coefficients related to DeltaVbe and are used for level shift, the reference voltage is raised and used for controlling a driving pole, and p5, p6, p7, R7 and R8 are used as driving poles together and used for controlling output of n 1.

2. The zero temperature coefficient reference circuit according to claim 1, wherein the bias circuit comprises PNP transistors p8-p10, a resistor R9, and NPN transistors n2, p8 and p9 having emitters connected VIN, bases connected to each other, p9 having a base connected to p9 collector and p10 emitter, p8 having a collector connected to p10 base and n2 collector, p10 having a collector connected to n2 base, p10 having a collector output of reference output Vref = 2.5v, n2 having an emitter connected to ground via R9;

The p8 and p9 mirror current sources VIN, p10 are used as negative feedback ends to realize the matching of p8 and p9 currents, and n2 and R9 are used for setting the bias currents of p8 and p9, and the current value is (Vref-Vbe_n2)/R9.

3. The zero temperature coefficient reference circuit of claim 1, wherein the PNP transistors of the reference core circuit are the same size.