Reference voltage generating circuit

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a reference voltage generating circuit that generates a DC reference voltage, and more specifically, a transistor base-emitter voltage Vbe having a negative temperature coefficient and a voltage having a positive temperature coefficient (base of two transistors). The present invention relates to an improvement of a bias circuit based on a band gap voltage having a low temperature coefficient by weighting and adding the difference ΔVbe) between the emitters.

【0002】

[Conventional technology]

Conventionally, this type of voltage generation circuit has been well known. For example, US Pat. No. 3,887,863 shows a voltage generation circuit as shown in FIG. This circuit has paired transistors Q01 and Q02 connected to the positive power supply line 1 via resistors RL1 and RL2, and the emitter of one of the transistors Q02 has a negative voltage via the resistors RE2 and RE1 connected in series. It is connected to line 2, and the emitter of the other transistor Q1 is connected to the common connection point of resistors R2 and R1.

【0003】

Further, the collector voltage of the transistors Q02 and Q01 is connected to the input terminal of the high gain operational amplifier 3, and the output of the operational amplifier 3 is connected to the output terminal 4 and connected to the base of the transistors Q02 and Q01.

【0004】

The difference between the base-emitter voltage of the two transistors Q01 and Q02 ΔVbe has a positive temperature coefficient, and the base-emitter voltage Vbe of the transistor Q01 has a negative temperature coefficient. It acts to cancel each other out. The output voltage Vout is set to approximately the energy bandgap voltage Vgo to bring the temperature coefficient (TC) closer to zero. Vgo is 1.205V for silicon, but excellent results can be obtained by setting the output voltage Vout to a voltage slightly higher than this.

【0005】

For example, the output voltage to make TC zero, Vout = Vgo + (m-1) kT₀/ q Set to. Here, m is a constant, almost 1.5, k is Boltzmann's constant, T₀Is the operating temperature and q is the charge of the electron.

【0006】

This output voltage Vout can be adjusted to a desired value by appropriately selecting the resistor RE1. Then, when the output Vout falls below the preset optimum level, the current ratio I of the transistors Q02 and Q01₂/ I₁Becomes larger than the resistivity ratio RL1 / RL2, the output of amplifier 3 increases, and the output voltage Vout is raised to the optimum level. When the output Vout becomes higher than the optimum level, the output of the amplifier 3 decreases and the output voltage Vout is lowered to the optimum level.

【0007】

The circuit shown in FIG. 4 operating as described above can continuously maintain the output voltage at a desired level with a low temperature coefficient.

【0008】

[Problems to be Solved by the Invention]

However, such a conventional circuit has the following problems. High-precision trimming such as laser trimming is required for optimum weighting by resistance. Even if appropriate weighting is applied, the temperature characteristic of ΔVbe is linear, whereas the temperature characteristic of Vbe is non-linear, so the temperature dependence of about ± 25 ppm / ° C remains.

【0009】

The present invention solves such a problem, and an object of the present invention is to provide a reference voltage generation circuit that generates a reference voltage that is not affected by changes in ambient temperature, based on a bandgap voltage having a low temperature coefficient. Is what you do.

【0010】

[Means for solving problems]

In order to achieve such an object, in the invention of claim 1, the emitters of a pair of transistors having different current densities are commonly connected to each other, and a voltage having a difference in voltage between the base and the emitter proportional to the temperature T is generated._TGeneration circuit and this V_TA non-linear ΔVbe generator that receives the output of the generator circuit and generates a ΔVbe with a current density ratio proportional to the temperature and outputs it by multiplying it by m, and a constant current Ic that flows through the transistor and the voltage Vbe between the base and emitter of this transistor. It is characterized in that it includes a Vref output circuit that outputs by adding the output of the non-linear ΔVbe generation circuit, and is configured so that an output voltage equal to the band cap voltage can be obtained from this Vref output circuit.

【0011】

V_TThe m × ΔVbe is obtained by the generation circuit and the non-linear ΔVbe generation circuit, and the voltage Vref obtained by adding Vbe to the m × ΔVbe is output in the Vref output circuit. The voltage Vref at this time is as follows. Voltage Vref = Vbe + m × ΔVbe = Vgo-(kT / q) ln {(KT)^r) / (IcN^m)} However, Vgo is the bandgap voltage of Si at an absolute temperature of 0 degrees, k is the Boltzmann constant, T is the absolute temperature, q is the elementary charge, K is the constant independent of temperature, r is the constant that is alien to the process, and Ic is the constant current. , N is V_TCurrent density ratio in the generator circuit, m is the magnification of the nonlinear ΔVbe generator circuit [0012]

At this time, N^m= KT^r/ Ic = AT^rBy setting (A is a term that does not include temperature), Vref = Vgo can be set, and a bandgap reference voltage generation circuit that does not depend on temperature can be realized.

【0013】

In this case, as a non-linear ΔVbe generating circuit, V, for example, as in claim 2._TA current proportional to the temperature output from the generating circuit via the resistor and a current obtained by passing a constant voltage from the regulated voltage source through a resistor having a temperature coefficient equal to the resistor are allowed to flow into the pair of transistors. , Can be configured to generate ΔVbe with a current density ratio proportional to temperature.

【0014】

Further, as a non-linear ΔVbe generation circuit, for example, as in claim 3, V_TObtain the log of the current corresponding to the voltage difference between the base and emitter voltage proportional to the temperature T from the generating circuit. Obtain the log of the current corresponding to the constant voltage from the first log amplifier and the regulated voltage source. It can be composed of a logarithmic conversion circuit that outputs the difference in output from the second log amplifier and an m times circuit that multiplies the voltage of the difference between the outputs of the two log amplifiers by m.

【0015】

Also, as in claim 4, V_TA pair of transistors of the generation circuit and the non-linear ΔVbe generation circuit can be configured by connecting the transistors in series in three stages. Such a configuration has the effect of reducing the influence of package stress when the circuit of the present invention is made into an IC.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail. The present invention is a reference voltage generation circuit based on a bandgap voltage.

【0017】

The output voltage (bandgap reference voltage Vref) in the circuit of the present invention can be expressed by the following model equation. Vref = Vbe + m × ΔVbe = {Vgo- (kT / q) ln (KT^r/I c)} + {m × (kT / q) ln (N)} = Vgo-(kT / q) ln (KT^r/ (IcN^m)} ...... (1) Here, m is a coefficient representing the magnification, Vgo is the bandgap voltage of silicon (Si) at zero degrees of absolute temperature, T is the absolute temperature, ln is the natural logarithm symbol, N is the current density ratio, and r is a process-dependent constant. , Ic is the current value, k is the Boltzmann constant, and K is a temperature-independent constant.

【0018】

Here, the expansion formula of Vbe in the formula (1) will be described. First, the general formula of Vbe is as follows. Vbe = (kT / q) ln (Ic / Is) ...... (2) Here, Is is the reverse saturation current and has the following relationship.

【0019】

Is = qDAn²/ Q However, D is the diffusion coefficient, A is the junction area of the emitter base, n is the intrinsic carrier density, and Q is the amount of impurities per unit area in the base. Of these, q, A, and Q are invariant with respect to temperature, and if this is a constant B, the above equation will be: Is = BDn² ...... (3) Will be.

【0020】

Substituting Einstein's relation D = kTμ / q (μ is the carrier mobility) Is = kTμBn²/ q ...... (4) Will be. Furthermore, since k and q are invariant to temperature, if this is included in B and a new constant C is used, Is = CT μn² ......(Five) Will be.

【0021】

Carrier mobility μ is μ = ET^xCan be expressed as. Here, E is a temperature-invariant term, and the multiplier x of T is a value that changes with the impurity concentration in the base region. Also, as is well known, the intrinsic carrier density is known. n²= (FT³) exp (-Vgo / Vt) ...... (6) Is. Here, F is a value that is invariant to temperature. Also, Vt = kT / q.

【0022】

Μ and n above²Is substituted into Eq. (2) and expanded, the relational expression in Eq. (1), Vbe = Vgo-(kT / q) ln (kT^γ/I c) Is obtained.

【0023】

Now, in equation (1), N^m= KT^rBy setting / Ic = AT (A is a temperature-independent coefficient), that is, V_TBy making the current density ratio N in the generation circuit proportional to the temperature and setting m = r, the second term of Eq. (1) can be made zero, so the term including the variation of the element can be canceled and the term can be canceled. A temperature-independent bandgap reference voltage can be obtained. The present invention has realized a reference voltage generation circuit that is not affected by changes in ambient temperature based on such a principle.

【0024】

FIG. 1 is a configuration diagram showing an embodiment of a reference voltage generation circuit according to the present invention. In this reference voltage generation circuit, the emitters of a pair of transistors with different current densities are commonly connected to generate a voltage difference between the base and emitter that is proportional to the temperature._TGeneration circuit 10 and this V_TA non-linear ΔVbe generation circuit 20 that generates ΔVbe with a current density ratio proportional to the temperature from the output of the generation circuit 10 and multiplies it by m, and a constant current Ic is passed through a transistor to generate Vbe and is added to the output of the non-linear ΔVbe generation circuit 20. It is composed of a Vref output circuit 30 that generates a reference voltage Vref.

【0025】

Each part will be described in more detail below. V_TIn the generation circuit 10, the pair transistors Q0 and Q3 with the emitters commonly connected and the resistors R0 and R1 (resistors) with one end connected to the high-voltage side power supply (voltage Vcc) and the other end connected to the collectors of the transistors Q0 and Q3, respectively. The ratio is N to 1), the constant current source 17 with one end connected to the emitter of the transistors Q0 and Q3 and the other end connected to the low voltage source (voltage Vee), and the collector voltage of the transistors Q0 and Q3 are differential. It is composed of an arithmetic amplifier OP10 whose output is connected to the base of transistor Q3 and a resistor R2 which is connected between the bases of transistors Q0 and Q3.

【0026】

According to such a connection, between the bases of transistors Q0 and Q3, V_T= (kT / q) lnN Voltage V_TTherefore, the resistance R2 (the resistance value is R)₂) I₁= (kT / qR₂) lnN Current I₁Flows.

【0027】

The non-linear ΔVbe generation circuit 20 is composed of a pair of logarithmic amplifiers Q6 and Q9, an operational amplifier OP11, a resistor R3, an operational amplifier OP12 as a buffer amplifier, and a series connection circuit formed by connecting resistors R4 and R5 in series. To.

【0028】

Transistors are used here as log amplifiers Q6 and Q9 (Q6 is called the first log amplifier and Q9 is called the second log amplifier). V for the collector of Q6_TCurrent generated in generating circuit 10 I₁On the other hand, the current I flowing through the resistor R3 goes to the collector of Q9.₂Inflow. This current I₂Is a resistor R3 (resistor value is R)₃) Reference voltage V_AJIt is possible to adjust by. The base of transistor Q9 is connected to the common line gnd.

【0029】

The non-inverting input terminal of the operational amplifier OP11 is connected to the common line, the inverting input terminal is connected to the collector of the transistor Q9, and the output terminal is commonly connected to the emitters of the transistors Q6 and Q9. In this case, the inverting input terminal of the operational amplifier OP11 has a common line potential equivalently, and one end of the resistor R3 has a common line potential.

【0030】

The non-inverting input terminal of the operational amplifier OP12 is connected to the collector of the transistor Q6, and the output terminal connected to the inverting input terminal is connected to the resistors R4 and R5 in a series connection circuit. The common connection point of the resistors R4 and R5 is connected to the base of the transistor Q6.

【0031】

When the resistor R4 and the resistor R5 are m = (R4 + R5) / R5, a voltage m × ΔVbe, which is m times the voltage ΔVbe at the midpoint of the series connection circuit, is generated at the output end of the operational amplifier OP12. , The part consisting of the operational amplifier OP12 and the series connection circuit is called an m times circuit here. The voltage ΔVbe at the midpoint of the series connection circuit is the difference between the base-emitter voltage of the transistor Q6 and the transistor Q9.

【0032】

The Vref output circuit 30 includes a constant current source 18, a buffer 16, and a transistor Q12. One end of the constant current source 18 is connected to the high-voltage side power supply, and the other end is connected to the collector of the transistor Q12. The emitter of the transistor Q12 is connected to the output end of the operational amplifier OP12 of the nonlinear ΔVbe generation circuit 20.

【0033】

The input end of buffer 16 is connected to the collector of transistor Q12, and the output end is connected to the base of transistor Q12 and the output end Vref OUT.

【0034】

The operation in such a configuration will be described below. V_TCurrent I flowing through resistor R2 of generation circuit 10₂Is I₂= (kT / qR2) lnN This current flows through the transistor Q6. The base-emitter voltage Vbe1 of the transistor Q6 at this time is as follows. Vbe1 = (kT / q) ln (I₁/ I_s) = (kT / q) ln {(kT / (q Is R2)) lnN} [0035]

On the other hand, the transistor Q9 has the current I flowing through the resistor R3.₂= V_AJ/ R3 is input, and its base-emitter voltage Vbe2 is as follows. Vbe2 == (kT / q) ln (I₂/ I_s) = (kT / q) ln (V_AJ/ (Is R3) [0036]

Therefore, the voltage ΔVbe at the midpoint of the voltage divider circuit is ΔVbe = Vbe1-Vbe2 = (kT / q) ln (CT / V_AJ) However, C = {kR3 / (qR2)} lnN, and the voltage m × ΔVbe at the output end of the operational amplifier OP12 is m × ΔV be = m × (kT / q) ln (CT / V_AJ) = (kT / q) ln (CT / V_AJ)^mHowever, m = (R4 + R5) / R5.

【0037】

Therefore, the voltage Vref of the output terminal Vref OUT of the Vref output circuit 30 is Vref = Vbe + m × ΔVbe = Vgo-(kT / q) ln {(V_AJ^mKT^r) / (I_cC^mT^m)} Will be. Where r = m, V_AJ^mK = I_cC^mThen Vref = Vgo Therefore, a reference voltage that is not affected by changes in ambient temperature can be obtained.

【0038】

According to the present invention, by adjusting the output to the known constant voltage Vgo in this way, the variation can be canceled and the temperature coefficient ± 0 ppm / ° C can be realized. However, when this circuit is realized by an IC, the bandgap voltage in each transistor changes due to the package stress, and some constant term is added to the above logical formula, so that one-point adjustment becomes difficult to realize.

【0039】

The example configuration diagram of FIG. 2 is an example of a circuit configuration capable of reducing the influence of such package stress. That is, V_TA pair of transistors of the generation circuit 10 and the non-linear ΔVbe generation circuit 20 are stacked in several stages (three stages in the figure), and the influence of stress is easily reduced by this.

【0040】

Further, in the circuit configuration of FIG. 2, since the magnification of the m-fold circuit of the nonlinear ΔVbe generation circuit 20 can be reduced (it can be reduced to m / 3), the error is not greatly amplified and it is extremely practical. It is valid.

【0041】

Figure 3 shows the temperature characteristics of the output voltage in comparison with the conventional example. The circle plot is the characteristic of the reference voltage generation circuit of the present invention, and the square plot is the characteristic of the conventional circuit. It can be seen that the temperature characteristics of the present invention are remarkably superior to those of the conventional invention, and the fluctuation due to temperature is extremely small. The diagonal straight lines shown for reference represent temperature changes of + 25 ppm / ° C and -25 ppm / ° C.

【0042】

[Effect of the invention]

As described above, the present invention has the following effects. According to the invention of claim 1, a temperature-independent bandgap reference voltage can be easily generated.

【0043】

Further, by configuring as in claim 4, it is possible to easily realize a circuit that reduces the influence of package stress.

[Simple explanation of drawings]

[Figure 1]

It is a block diagram which shows one Example of the reference voltage generation circuit which concerns on this invention.

[Figure 2]

It is a block diagram which shows the other Example of this invention.

[Fig. 3]

It is a temperature characteristic comparison diagram of the reference voltage generation circuit of this invention and the conventional circuit.

[Fig. 4]

It is a block diagram which shows an example of the conventional reference voltage generation circuit.

[Explanation of symbols]

10 V_TGeneration circuit 16 buffer 17,18 constant current source 20 Non-linear ΔVbe generation circuit 30 Vref output circuit Q0, Q3, Q6, Q9, Q12 transistors R0, R1, R2, R3, R4, R5 resistors OP10, OP11, OP12 op amp