A zero temperature coefficient reference circuit

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

Technical Field

[0001] The invention belongs to the technical field of integrated circuits, relates to power management of integrated circuits, and in particular to a bandgap reference technology, which is a reference circuit with a zero temperature coefficient. Background Art

[0002] The traditional bandgap reference is 1.25V, but some industrial applications use a 2.5V reference source, so they use a double bandgap reference voltage, and use an op amp circuit to achieve the double reference, which requires consideration of loop stability. Since the system circuit of this double bandgap reference voltage is relatively complex, the reference chip area is large, resulting in higher costs. For example Figure 1 The figure shows a traditional 2.5V reference circuit, where the voltage at the REF terminal is 2.5V. Two compensation capacitors are required inside the circuit for loop stability, namely the output Miller compensation A of the first stage of the op amp, and the compensation capacitor B of the input terminal of the Darlington tube to CATHODE. Since the capacitors in the bipolar process generally have a relatively small block value, these two capacitors occupy about half of the total chip area. Summary of the invention

[0003] The technical problem to be solved by the present invention is that in the design of the 2.5V reference source of the existing bandgap reference circuit, an additional compensation circuit is required, the circuit is complex and the circuit area is large.

[0004] The technical solution of the present invention is: a reference circuit with a zero temperature coefficient, 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, a current source VIN generates a bias current through the bias circuit to power the reference core circuit, the reference core circuit includes PNP tubes p1-p7, resistors R1-R9 and NPN tube n1, and the reference core circuit is as follows:

[0005] The bias current output is connected to ground via R1 and p1, connected to ground via p2, R2 and R3, connected to ground via R4 and p3, connected to ground via R5, p4 and R6, connected to ground via p5, R7 and p6, connected to ground via p7 and R8, and connected to ground via 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 to the collector of p5, 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;

[0006] The output end of the bias circuit is the reference voltage, and n1 is used to pull down the bias circuit current source to form a stable reference output; R1, R2, R3, p1, and p2 are used to set the temperature coefficient of the reference circuit, and by adjusting the resistance ratio of R1, R2, and R3, a negative temperature coefficient current related to the Vbe of p1 and p2 is achieved; p3, p4, R4, R5, and R6 are used to achieve a positive temperature coefficient related to ΔVbe, and are also used for level shifting to raise the reference voltage for controlling the drive pole; p5, p6, p7 and R7, R8 are used together as drive poles to control the output of n1.

[0007] Furthermore, the bias circuit includes PNP tubes p8-p10, resistor R9 and NPN tube n2, the emitters of p8 and p9 are connected to VIN, the bases are connected to each other, the base of p9 is also connected to the collector of p9 and the emitter of p10, the collector of p8 is connected to the base of p10 and the collector of n2, the collector of p10 is connected to the base of n2, the collector output of p10 is also the reference output Vref=2.5V, and the emitter of n2 is grounded via R9;

[0008] Among them, p8 and p9 mirror current source VIN, p10 is used as a negative feedback terminal to achieve the matching of p8 and p9 currents, n2 and R9 are used to set the bias current of p8 and p9, and the current value is (Vref-Vbe_n2) / R9.

[0009] The present invention provides a new 2.5V reference technology, which can achieve reference stability by using a simple loop, does not require a compensation circuit, has a simple circuit structure, a clear principle, and is easy to implement. At the same time, the present invention can achieve a 2.5V reference with a zero temperature coefficient through a small-scale circuit structure, which can save chip area and reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a circuit diagram of a 2.5V reference circuit in the prior art.

[0011] Figure 2 The circuit diagram of the zero temperature coefficient 2.5V reference circuit of the present invention is shown in FIG.

[0012] Figure 3 This is a circuit simulation effect diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0013] Combine the following Figure 2 The implementation of the present invention will be described in detail.

[0014] The reference circuit of the present invention 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. A current source VIN generates a bias current through the bias circuit to supply power to the reference core circuit. The reference core circuit includes PNP tubes p1-p7, resistors R1-R9 and an NPN tube n1. The bias circuit includes PNP tubes p8-p10, a resistor R9 and an NPN tube n2.

[0015] The benchmark core circuit is as follows:

[0016] The bias current output is grounded through R1 and p1, through p2, R2 and R3, through R4 and p3, through R5, p4 and R6, through p5, R7 and p6, through p7 and R8, and through n1, that is, the output of the bias circuit is grounded through 7 paths, among which 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 to the collector of p5, 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.

[0017] The bias circuit is as follows:

[0018] In the bias circuit, the emitters of p8 and p9 are connected to VIN, the bases are connected to each other, the base of p9 is also connected to the collector of p9 and the emitter of p10, the collector of p8 is connected to the base of p10 and the collector of n2, the collector of p10 is connected to the base of n2, the collector output of p10 is also the reference output Vref=2.5V, and the emitter of n2 is grounded through R9.

[0019] The output of the bias circuit is the reference voltage, that is, the collector output Vref of p10, the mirror current source VIN of p8 and p9, and p10 as the negative feedback terminal to achieve the matching of the current of p8 and p9. n2 and R9 are used to set the bias current of p8 and p9, and the current value is (Vref-Vbe_n2) / R9, and Vbe_n2 represents the Vbe of n2. 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 to set the temperature coefficient. By adjusting the resistance ratio of R1, R2, and R3, a negative temperature coefficient current related to the Vbe of p1 and p2 is achieved. p3, p4, R4, R5, and R6 are used to achieve a positive temperature coefficient related to ΔVbe, and are also used for level shifting to raise the reference voltage for controlling the driving pole. p5, p6, p7, and R7 and R8 are used together as driving poles to control the output of n1. The connection between the base and collector of p5 is conducive to the micro-conduction of p7 and avoids oscillation caused by the complete shutdown of n1.

[0020] The circuit of the present invention realizes a 2.5V reference with a zero temperature coefficient, which is explained below through an example embodiment.

[0021] In this embodiment, the PNP tubes of the reference core circuit have the same size. Assuming r is the unit resistance value, R1=7*r, R2=0.25*r, R3=6.5*r, R4=70*r, R5=6*r, R6=84*r, R7=23*r, and R8=12*r are set. Among the 7 paths of the reference core circuit, the path current corresponding to R1 is set to I1, the path current corresponding to p2 is set to I2, the path current corresponding to R4 is set to I3, and the path current corresponding to R5 is set to I4. It can be achieved that I1=I2, I3=I4, and I1=10 x I3. I3=I is used as the unit current value. In this way, the Vbe of p1 and p2 are equal, and the Vbe of p3 and p4 are equal, which simplifies the calculation.

[0022] According to the reference circuit of the present invention, for the reference voltage Vref:

[0023] Vref=Vbe_p2+Vbe_p1+I2*R3= Vbe_p3+Vbe_p4+I4*R5+ I2*(R2+R3)

[0024] It can be obtained that 2*ΔVbe= Vbe_p2+Vbe_p1-(Vbe_p3+Vbe_p4)= I2*R2+ I4*R5

[0025] For PNP tube, Vbe= VT*ln(Ic / Is) is obtained from Ic=Is*exp(Vbe / VT), where Ic is the emitter-to-collector current and Is is the saturation current. T=kT / q is the thermal voltage, k is the Boltzmann constant, q is the electron charge, and T is the temperature in Kelvin. VT is proportional to the temperature T. Vbe is the base-emitter voltage.

[0026] Therefore, there is

[0027] 2*ΔVbe= Vbe_p2+Vbe_p1-(Vbe_p3+Vbe_p4)

[0028] =VT* ln(Ic_p2 / Is)+ VT* ln(Ic_p1 / Is)- VT* ln(Ic_p3 / Is)- VT* ln(Ic_p4 / Is)

[0029] = VT* ln[Ic_p2* Ic_p1 / ( Ic_p3* Ic_p4)]

[0030] = VT* ln100=4.6*VT;

[0031] It can be obtained that ΔVbe=2.3*VT, that is, ΔVbe is proportional to VT and temperature T.

[0032] Combining the above formula, we can get: 2*ΔVbe=4.6*VT= I2*R2+ I4*R5

[0033] That is, ΔVbe is a positive temperature coefficient. At the same time, the product of the unit current I and the unit resistance r is related to VT, showing a positive temperature coefficient.

[0034] According to the block value on the circuit, that is, the resistance value of the above resistor based on the unit resistance, we can get:

[0035] I2*R2+ I4*R5=10*I*0.25r+I*6R=8.5*I*r

[0036] Equivalent to I*r=4.6*VT / 8.5.

[0037] Since I*r and VT are both proportional to ΔVbe and have positive temperature coefficients, combined with the negative temperature coefficient of Vbe, a zero temperature coefficient can be achieved by using I2*R3 with a certain constant ratio to ΔVbe, such as a constant α.

[0038] Vref=Vbe_p2+Vbe_p1+α*ΔVbe=Vbe_p2+Vbe_p1+I2*R3,

[0039] Set the appropriate resistance value so that I2*R3=65*I*r, which is approximately equal to 34.4*VT.

[0040] Theoretically, the temperature coefficient of VT is about 0.087mV / оK, and the temperature coefficient of Vbe is about -1.5 mV / оK. From the textbook, we can get that when Vref=Vbe+17.2VT is approximately zero temperature coefficient.

[0041] Corresponding to this reference circuit:

[0042] Vref=Vbe_p2+Vbe_p1+α*ΔVbe =Vbe_p2+Vbe_p1+I2*R3= Vbe_p2+Vbe_p1+34.4*VT

[0043] The theoretical zero temperature coefficient reference value Vref=2.5V of the reference circuit of the present invention can be obtained.

[0044] In summary, the present invention can realize a reference voltage of Vref=2.5V with a zero temperature coefficient by using a simple circuit, does not require a compensation circuit and a capacitor, and can significantly reduce the chip area.

[0045] right Figure 2The circuit is simulated under the following conditions: using power supply VDD = 5V, scanning temperature characteristics, the simulation results are as follows Figure 3 As shown, when the temperature T is -40 to 180 degrees, Vref changes by 37 mV, corresponding to a temperature coefficient of about 1.5%, which meets the design requirements. The circuit of the present invention can effectively achieve the effect of a zero temperature coefficient reference.

Claims

1. A zero temperature coefficient reference circuit, characterized in that The reference circuit of the 2.5V reference source is composed of a triode and a resistor. The reference circuit includes a bias circuit and a reference core circuit. The current source VIN generates a bias current through the bias circuit to power the reference core circuit. The reference core circuit includes PNP tubes p1-p7, resistors R1-R9 and NPN tube n1. The reference core circuit is as follows: The bias current output is connected to ground via R1 and p1, connected to ground via p2, R2 and R3, connected to ground via R4 and p3, connected to ground via R5, p4 and R6, connected to ground via p5, R7 and p6, connected to ground via p7 and R8, and connected to ground via 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 to the collector of p5, 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 the reference voltage, and n1 is used to pull down the bias circuit current source to form a stable reference output; R1, R2, R3, p1, and p2 are used to set the temperature coefficient of the reference circuit, and by adjusting the resistance ratio of R1, R2, and R3, a negative temperature coefficient current related to the Vbe of p1 and p2 is achieved; p3, p4, R4, R5, and R6 are used to achieve a positive temperature coefficient related to ΔVbe, and are also used for level shifting to raise the reference voltage for controlling the drive pole; p5, p6, p7 and R7, R8 are used together as drive poles to control the output of n1.

2. A zero temperature coefficient reference circuit according to claim 1, characterized in that The bias circuit includes PNP tubes p8-p10, resistor R9 and NPN tube n2. The emitters of p8 and p9 are connected to VIN, and the bases are connected to each other. The base of p9 is also connected to the collector of p9 and the emitter of p10. The collector of p8 is connected to the base of p10 and the collector of n2. The collector of p10 is connected to the base of n2. The collector output of p10 is also the reference output Vref=2.5V. The emitter of n2 is grounded through R9. Among them, p8 and p9 mirror current source VIN, p10 is used as a negative feedback terminal to achieve the matching of p8 and p9 currents, n2 and R9 are used to set the bias current of p8 and p9, and the current value is (Vref-Vbe_n2) / R9.

3. A zero temperature coefficient reference circuit according to claim 1, characterized in that The PNP tubes of the benchmark core circuits are the same size.

Images