JPH09204233A - Circuit for generating reference voltage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the influence of temp. change by keeping the linearity of a voltage between the base and the emitter of a transistor which obtains a bandcap voltage. SOLUTION: The voltage obtained by the transistors Q19 and 20 of a level- shift circuit 5 is level-shifted to the emitter of the third transistor Q 18 and its voltage is added to the base of the second transistor Q2. The collector of the transistor Q2 is connected to a second current source S2 and a third current mirror circuit 3 so that prescribed current is permitted to flow in a connection point 9 and the current is equal to the one which flows in the third current mirror circuit 3. The current is also equal to the collector current Ic1 of the first transistor Q1. Therefore, the collector current Ic1 of the transistor Q1 perfectly changes by the square characteristic as against temp. change. Then, collector current Ic1 having a positive coefficient for the square term is permitted to flow so that the term which changes in accordance with the square characteristic of the voltage VBE1 between the base and the emitter is cancelled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference voltage generating circuit capable of obtaining an accurate bandgap voltage without being affected by temperature change.

[0002]

2. Description of the Related Art The bandgap voltage is used as a reference voltage because it is not easily affected by temperature changes. FIG. 2 is a circuit diagram of a known bandgap reference circuit (hereinafter referred to as BG circuit), which includes transistors Q3, Q4, Q6.
Further, it is formed of a transistor Q5 having a multi-emitter, a resistor R1 and a resistor R2. 8 is the power supply voltage V _CC
Is a power supply terminal, and 7 is an output terminal. If the collector current I ₆ of the collector current I ₅ and the transistor Q6 of the transistor Q5 is equal, is obtained from a bandgap voltage V _G is terminal 7 shown in (1). V _G = 2I ₅ · R2 + V _BE6 = {2R2 · V _T · Ln (N) / R1} + V _BE6 (1)

Where R1 and R2 are resistance values of the resistors R1 and R2, V _BE6 is a base-emitter voltage of the transistor Q6, V _T is a thermal voltage, and Ln is a symbol of natural logarithm.
N is the number of emitters of the transistor Q5. Thermal voltage V
Temperature coefficient of _T is positive in (0.085mV / ° C), since the temperature coefficient of the base-emitter voltage V _BE6 is negative extent (-2mV / ° C), ( 1) the resistance value in the equation R1, R2 The bandgap voltage V _{G that is} not affected by temperature changes can be selected by selecting
Is obtained. However, when measured precisely, the bandgap voltage V _G is still affected by the temperature change.

This is because the base-emitter voltage V _BE of the bipolar transistor is represented by the equation (2). V _BE = {1- (T / T ₀ )} V _G0 + T · V _BE0 / T ₀ + (nkT / q) Ln (T ₀ / T) + (kT / q) Ln (I _C / I _C0 ) ( 2) Expression (2) is obtained by substituting Expression (4) into Expression (3). V _BE = (kT / q) Ln (I _C / I _S ) (3) I _S = qAn _i ² D _n / Q _B (4) In the formulas (2) to (4), q is an electron. Electric charge, A is the emitter-base junction area, _ni is the intrinsic carrier concentration of silicon, D _n is the average effective value of the diffusion coefficient of electrons in the base, Q _B is the total amount of impurities per unit area in the base, and k is Boltzmann constant, I _C is collector current, I _S
Is saturation current, T is absolute temperature, T ₀ is reference temperature, V _BE0 and I _C0 are base-emitter voltage and collector current at reference temperature T ₀ , V _G0 is estimated value of silicon bandgap voltage, and n is a constant Is.

In the equation (2), the first two terms change while maintaining a straight line with respect to the temperature change, while the third term changes due to the square characteristic. FIG. 3 is a diagram showing changes in the value of the third term, where the horizontal axis represents the absolute temperature T and the vertical axis represents the value f (T) of the third term. Since f (T) is expressed by equation (5), the coefficient of the squared term is negative. f (T) = (nk / q) Ln (T 0) · T- properties of (nk / q) Ln (T ) · T (5) such a base-emitter voltage V _BE is a bandgap voltage It is clear that the same occurs in the obtained base-emitter voltage V _BE6 of the transistor Q6. Then, does not change linearly with the temperature coefficient of exactly due to the presence of the voltage V _BE6 is the square of the term (-2mV / ° C), the band gap voltage V _G can not be avoided still the influence of temperature change. The fourth term in the equation (2) has a small value and can be ignored.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to obtain the bandgap voltage of a BG circuit from the base of a transistor in which the base-emitter voltage changes while maintaining linearity, so that the effect of temperature change is completely eliminated. It is to provide a reference voltage generation circuit that can be removed.

[0007]

A reference voltage generating circuit according to the present invention comprises a first, a second, a third and a fourth current mirror circuit, a level shift circuit, a first and a second current source, and a first and a second current source. The second current mirror circuit is composed of a second transistor and a BG circuit, the first current mirror circuit is composed of a pair of transistors including the one-side transistor having a multi-emitter, and the second current mirror circuit is composed of the first transistor.
Is connected as a load to the current mirror circuit, the level shift circuit is diode-connected to each other in series, and another pair of transistors through which the current of the second current mirror circuit flows and the first current source to the emitter are connected. A second transistor connected to its emitter for level shifting the voltage obtained by the other pair of transistors;
Is connected to the second current mirror circuit, the third current mirror circuit, the second current source and the level-shifted voltage is applied to the base, and the third current mirror circuit is connected to the fourth current mirror circuit. Connected as a load of the circuit, the first transistor is connected between the third current mirror circuit and the fourth current mirror circuit, the transistor for obtaining the bandgap voltage of the BG circuit and the emitter are commonly connected, and It is characterized in that the bandgap voltage is obtained from the base of the transistor.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION By flowing a collector current containing a quadratic term having a temperature as a variable in a first transistor,
While canceling the term that changes depending on the square characteristic of the base-emitter voltage, the emitter of the first transistor and the transistor for obtaining the bandgap voltage of the BG circuit are commonly connected, and the bandgap voltage is used as a reference from the base of the first transistor. It is obtained as a voltage.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the reference voltage generating circuit of the present invention will be described below with reference to FIG. The same parts as those in FIG. 2 are denoted by the same reference numerals. In FIG. 1, a transistor Q16 having M multi-emitters and a transistor Q17 form a first current mirror circuit 1, an emitter of the transistor Q16 is grounded via a resistor R3, and an emitter of a bias side transistor Q17 is directly grounded. To be done. The transistors Q12, Q13, Q14, Q15 form a second current mirror circuit 2 and are connected as a load of the first current mirror circuit 1. The collector of the bias side transistor 14 is the collector of the transistor 16 and the collector of the transistor Q15 is the transistor Q.
17 and the emitters of the respective transistors are connected to the power supply terminal 8.

The third transistor Q18 and the transistors Q19 and Q20 form a level shift circuit 5,
Transistors Q19 and Q2, which are diode-connected to each
0 are connected in series, and the collector of the transistor Q19 is the second
Of the current mirror circuit 2 is connected to the collector of the transistor Q13, and the emitter of the transistor Q20 is grounded.
The collector of the third transistor Q18 is connected to the terminal 8, and the emitter of the third transistor Q18 is grounded via the first current source S1. The collector of the second transistor Q2 is the transistor Q12.
The collector of the transistor Q9 is connected to the second current source S2, the base is connected to the emitter of the third transistor Q18, and the emitter is grounded.

Transistors Q7, Q8, Q9 form a third current mirror circuit 3 and bias side transistor 9
Is grounded via the second current source S2 and the emitter of each transistor is connected to terminal 8. The transistors Q10 and Q11 form a fourth current mirror circuit 4, and the emitters of the respective transistors are grounded. The third current mirror circuit 3 is connected as a load to the fourth current mirror circuit 4, and the collector of the transistor Q7 is connected to the collector of the transistor Q10 via the diode-connected first transistor Q1.
The collector of 8 is connected to the collector of transistor Q11.

The transistors Q3, Q4, Q5, Q6, the resistor R1, and the resistor R2 form a BG circuit 6, and a multi-emitter transistor Q5 having N emitters.
And the base of the transistor Q6 is connected. The emitter of the transistor Q5 is grounded via the resistors R1 and R2, and the connection point of the resistors R1 and R2 is connected to the emitter of the transistor Q6. The collectors of the transistors Q6 and Q4 on the bias side and the collectors of the transistors Q3 and Q5 are connected, and the emitters of the transistors Q3 and Q4 are connected to the power supply terminal 8. The emitter of the transistor Q6 for obtaining the bandgap voltage of the BG circuit 6 and the emitter of the first transistor Q1 are connected to each other, and the bandgap voltage is obtained from the output terminal 7 connected to the collector of the transistor Q1.

In the reference voltage generating circuit thus constructed, the fourth current mirror circuit 4 prevents the current flowing through the first transistor Q1 from flowing into the BG circuit 6. Further, the first current mirror circuit 1 functions as a current source circuit for flowing the current I _P shown by the equation (6). In addition,
In the formula (6), t represents temperature. I _P = {k (273 + t) / qR1} Ln (M) (6) This current I _P also flows into the second current mirror circuit 2, and the transistor Q19 connected in series in the level shift circuit 5
It also flows to Q20.

The voltage obtained by the transistors Q19 and Q20 is level-shifted to the emitter of the third transistor Q18, and the level-shifted voltage is applied to the base of the second transistor Q2. The base-emitter voltage V _BE2 of the transistor Q2 is expressed by the equation (7). _{V BE2 = V BE20 + V BE19} -V BE18 (7) V BE18, V BE19, V BE20 are each transistor Q18, Q
19 and the base-emitter voltage of Q20.

Since the relation between the base-emitter voltage and the collector current of each transistor is expressed by the equation (3),
The collector current I _C2 of the transistor Q2 is expressed by the equation (8). I _C2 = I _C20 · I _C19 / I _S1 = I _P ² / I _S1 (8) I _C20 and I _C19 are the collector currents of the transistors Q 20 and Q 19, respectively, and I _S1 is the current of the current source S 1. The collector of the second transistor Q2 is connected to the second current mirror circuit 2, the second current source S2, and the third current mirror circuit 3, so that the connection point 9 has the current represented by the formula (9). Flows, and this current is equal to the current flowing through the third current mirror circuit 3. Also, this current is equal to the collector current I _C1 of the first transistor Q1. I _C1 = {(I _P ² / I _S1 ) −I _P + I _S2 } (9) I _S2 is the current of the second current source S2.

Since the current I _P represented by the equation (6) is a linear equation having the temperature t as a variable, it is represented by (at + b). Equation (10) is obtained from equation (9). ^{_{I C1 = {(at) 2}} + 2abt + b 2 -I S1 (at + b) + I S1 I S2} / I S1 = {(at) 2 + (2ab-aI S1) t-I S1 b + b 2 + I S1 I S2} / I _S1 (10) The first term of the temperature of the equation (10), that is, (2ab-aI _S1 )
t can be eliminated by the set value of the current I _S1 . The coefficient of the squared term is positive.

Therefore, the collector current I _C1 of the transistor Q1 changes completely with the square characteristic with respect to the temperature change. The temperature coefficient of the current I _P may be either positive or negative. FIG. 4 is a diagram showing changes in the current I _C1 , and the horizontal axis represents the absolute temperature T. The shape of the curve of the squared characteristic can be adjusted by the current I _S2 of the current source S2. The collector current I _C1 and the base-emitter voltage V _BE1 of the transistor Q1, (3) V _BE, the I _C V _BE1, I in the equation
_Since there is a relationship in which the squared term is replaced with _C1 , the term that changes according to the squared characteristic of the base-emitter voltage V _BE1 represented by the equation (2) is canceled by flowing the collector current I _C1 having a positive coefficient. be able to. And the voltage V
_BE1 can change with temperature while maintaining linearity. Then, the bandgap voltage V _G obtained from the output terminal 7 is expressed by the equation (11). V _G = 2I ₅ · R2 + V _BE1 = {2R2 · V _T · Ln (N) / R1} + V _BE1 (11) By changing the voltage V _BE1 while maintaining the linearity, the temperature to the band gap voltage V _G is changed. The effects of change can be completely eliminated.

FIG. 5 shows a reference voltage generating circuit according to the present invention and FIG.
FIG. 7 is a diagram showing how the bandgap voltage of the conventional BG circuit changes with temperature. However, the difference between the theoretical value and the measured value when the base-emitter voltage of the transistor that finally obtains the bandgap voltage changes at (-2 mV / ° C) is shown. The solid line is the difference between the measured value of the bandgap voltage of the circuit of the present invention and the theoretical value when the temperature coefficient of the base-emitter voltage V _{BE1 in} the equation (11) is (-2 mV / ° C). The dotted line is the difference between the theoretical value when measured values of the band gap voltage of the circuit of FIG. 2 and (1) the temperature coefficient of the base-emitter voltage V _BE6 of the equation (-2 mV / ° C). According to the invention, -40 ° C to 120 ° C
, The difference from the theoretical value is within ± 1 mV, and it is understood that the linearity of the voltage V _BE1 is maintained.

[0019]

As described above, the reference voltage generating circuit of the present invention maintains the linearity of the base-emitter voltage of the transistor that obtains the bandgap voltage, so that the accurate band excluding the influence of the temperature change is obtained. The invention is extremely practical when a gap voltage can be obtained as a reference voltage and a precise reference voltage is required.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a reference voltage generating circuit of the present invention.

FIG. 2 is a circuit diagram of a conventional BG circuit.

FIG. 3 is a diagram showing states of terms that change depending on a square characteristic of a base-emitter voltage of a transistor.

FIG. 4 is a diagram showing changes in the collector current of the first transistor of the reference voltage generation circuit of the present invention.

FIG. 5 is a diagram showing how the bandgap voltage of a reference voltage generation circuit of the present invention and a conventional BG circuit changes with temperature.

[Explanation of symbols]

 Q1 first transistor Q2 second transistor S1 first current source S2 second current source

Claims (1)

[Claims] 1. A first, a second, a third, and a fourth current mirror circuit, a level shift circuit, first and second current sources, first and second transistors, and a bandgap reference circuit. The current mirror circuit of No. 1 is composed of a pair of transistors including a transistor on one side having multiple emitters, the second current mirror circuit is connected as a load of the first current mirror circuit, and the level shift circuit is diode-connected, respectively. Connected to each other in series, and another pair of transistors through which the current of the second current mirror circuit flows, and the voltage obtained by the other pair of transistors are level-shifted to their emitters and connected to the first current source. The third transistor is connected to the second current mirror circuit, the third current mirror circuit, the second current source and the level of the second transistor is connected to the base. And a third current mirror circuit is connected as a load of the fourth current mirror circuit, a first transistor is connected between the third current mirror circuit and the fourth current mirror circuit, A reference voltage generating circuit characterized in that a transistor for obtaining a bandgap voltage of a bandgap reference circuit and an emitter are commonly connected, and a bandgap voltage is obtained from the first transistor.