JPH07230332A - Band gap type constant voltage generating circuit - Google Patents

Abstract

PURPOSE:To reduce the influence of variance of the power voltage to the output voltage in a comparatively simple constitution of a band gap type constant voltage generating circuit. CONSTITUTION:A band gap type constant voltage generating circuit consists of a band gap circuit 3 which includes the transistors TR Q1, Q2 and Q3 and the resistances R1, R2 and R3 and outputs the output voltage Vo, a current inverting amplifier 1 which includes the TR Q4, Q5 and Q6 between the circuit 3 and a supplied power Vcc, and a starting circuit 2 which includes the diodes D1, D2 and D3 and a resistance R4. In such a constitution, the voltage generating circuit can reduce the variance of the voltage Vo that is caused by the variance of the supplied power Vcc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandgap constant voltage generating technique, and more particularly, to reducing output voltage fluctuations caused by fluctuations in power supply voltage in a bandgap constant voltage generating circuit constructed on an integrated circuit. Related to effective technology.

[0002]

2. Description of the Related Art For example, in designing an analog circuit, it is necessary to obtain a stable voltage against various factors of variation. For example, in a high-resolution A / D converter, a D / A converter, or the like, a high-precision reference voltage circuit that also considers temperature compensation is required to guarantee the resolution. For such a purpose, for example, a bandgap type constant voltage generating circuit as illustrated in FIG. 3 has been used.

In the following description, the base current of the transistor and the influence of the Early effect will be ignored for simplicity. Therefore, the term "current of a transistor" means its emitter current (or collector current) unless otherwise specified. _{Also, I n, V BEn, I} sn, A En (n is a number) in the symbols in the formula, and the current of the transistors Q _n, the base-emitter voltage, reverse saturation current, as indicating the emitter area, in particular Use without notice.

The output voltage V _O in the conventional band gap type constant voltage generating circuit of FIG. 3 is expressed by the following equation.

[0005]

[Equation 1]

In a bipolar transistor, the base-emitter voltage is expressed by the following equation.

[0007]

[Equation 2]

Where k is Boltzmann's constant, T is absolute temperature, q is elementary charge of electron, V _T is thermal voltage, I _s is reverse saturation current (proportional to emitter area), and I is current of transistor. . Therefore, the base-emitter voltage V _BE11 of Q _11, Q _12, V _BE12 is

[0009]

[Equation 3]

[0010]

[Equation 4]

Then, the following equation holds.

[0012]

[Equation 5]

[0013]

[Equation 6]

Further, the following equation is established from the circuit configuration.

[0015]

[Equation 7]

[0016]

[Equation 8]

By selecting an appropriate value of R ₁₄ , the current of the transistor Q ₁₃ can be determined, and V _BE11 = V
It can be _BE13 . At this time, from equations 7 and 8,

[0018]

[Equation 9]

Substituting this into Equation 6, the following equation is obtained.

[0020]

[Equation 10]

Variables R ₁₁ , R ₁₂ included in the right side of the equation 10
Since both A _E11 and A _E12 are fixed constants in terms of the circuit and are designed so that R ₁₁ · A _E11 <R ₁₂ · A _E12 , K is a constant of 1 or more.

Using the equation 5, the equation 1 becomes the following equation.

[0023]

[Equation 11]

Considering the temperature coefficient of the output voltage,
The temperature coefficient of the base-emitter voltage of the transistor Q ₁₃ , which is the first term on the right side of Equation 11, is negative, and the second term on the right side is K>.
Since it is 1, it becomes positive, so that the temperature coefficient of the output voltage can be made zero by setting K appropriately. When the temperature coefficient of the output voltage V _O is calculated from Equation 11, the following equation is obtained.

[0025]

[Equation 12]

When the left side of the equation 12 is set to 0 (when the temperature compensation constant is set), the following equation holds.

[0027]

[Equation 13]

Substituting this into equation 11,

[0029]

[Equation 14]

The base-emitter voltage of Q ₁₃ is 0.7 V, its temperature coefficient is -1.8 mV / ° C, and absolute temperature is 300 K (2
7 ° C), the output voltage value is

[0031]

[Equation 15]

It becomes That is, the output voltage of the band gap type constant voltage generating circuit having the configuration of FIG. 3 is about 1.2 to 1.3V.

[0033]

However, in the conventional bandgap type constant voltage generating circuit illustrated in FIG. 3, the current of the transistor Q ₁₃ fluctuates under the influence of the power supply voltage as shown by the following equation. To do.

[0034]

[Equation 16]

Here, V _cc is the power supply voltage supplied.

Clearly from the equation (16), due to the fluctuation of V _cc ,
I ₁₃ varies. As a result, V _{BE 13} fluctuates (relationship of Expression 2), and the output voltage V _O changes from the relationship of Expression 14.
The ratio of the variation (dV _O / dV _cc) is about 1%.

As a circuit for improving the fluctuation of the power supply voltage, for example, P. Fufukan, first edition issued in 1990, P. R Gray / R. The circuit shown in FIG. 4 has been known as described in the publications such as "G. Meyer," translated by Minoru Nagata, "Analog Integrated Circuit Design Technology for VLSI (above)" P276, and the like.

In the circuit of FIG. 4, the current I ₂₁ of the transistor Q ₂₁ is changed.
Is

[0039]

[Equation 17]

Since the voltage between the differential input terminals of the operational amplifier 20 is almost 0, the following equation holds.

[0041]

[Equation 18]

[0042]

[Formula 19]

From the relationships of the equations 18, 19 and 2, the output voltage V _O is expressed by the following equation.

[0044]

[Equation 20]

From equations 17 and 19,

[0046]

[Equation 21]

Therefore, from equation 20,

[0048]

[Equation 22]

It becomes The circuit of FIG. 4 can almost completely cancel the influence of the fluctuation of the power supply voltage due to the circuit configuration. However, in order to realistically configure the operational amplifier 20,
It requires a considerable number of circuit elements, and the operational amplifier 2
The high gain of 0 causes other problems such as requiring a phase compensation design that does not cause circuit oscillation.

An object of the present invention is to provide a bandgap type constant voltage generating technique capable of reducing the influence of fluctuations in the power supply voltage on the output voltage with a relatively simple circuit configuration.

[0051]

In the present invention, FIG.
The feedback circuit is configured by using a simple and low-gain current inverting amplifier instead of the complex and high-gain operational amplifier as illustrated in FIG. 2, and as a result, at the stable operation point, the current of the transistor Q ₁₃ is band-gap constant. It is determined by the output voltage of the voltage generator. This makes it possible to generate a stable output voltage that is not affected by fluctuations in the power supply voltage. Further, in order to prevent the output voltage = 0V from becoming an operation stable point, a simple starting circuit is added.

[0052]

The operation of the bandgap type constant voltage generating circuit of the present invention will be described with reference to FIG.

First, the operation of the bandgap circuit 3 composed of the transistors Q ₁ , Q ₂ , Q ₃ and the resistors R ₁ , R ₂ , R ₃ is similar to that of the prior art shown in FIG. That is, the output voltage V _O is expressed by the following equation.

[0054]

[Equation 23]

The current inverting amplifier 1 inputs the current of the transistor Q ₃ and outputs the currents of the transistors Q ₁ and Q ₂ . That is, the following formula is established.

[0056]

[Equation 24]

Here, M is the amplification factor of the current inverting amplifier 1.

Further, the output voltage V _O is expressed by the following equation from the circuit configuration.

[0059]

[Equation 25]

[0060]

[Equation 26]

That is, the combination of the current inverting amplifier 1 and the bandgap circuit 3 makes the output voltage V _O that satisfies both equations (23) to (26) the stable operation point of the circuit (variables V _O , I ₁ , I ₂ , For 4 I ₃ , there are possible solutions that give stable points because of 4 equations, where V _BE1 ,
V _BE2 and V _BE3 are I ₁ and I, respectively, due to the relationship of _Equation 2.
₂ , because it is bound by I ₃ , it can be excluded from the variables. ).

In this case, after all, if the constant of temperature compensation as described in the description of the prior art of FIG. 3 is selected, V _O ≈1.2V
Is a stable point, but V _O = 0 can also be a stable point if only the relations of Expressions 23 to 26 are satisfied. That is, if V _O = 0, then I ₁ = I ₂ = I ₃ = 0, and the equations 23 to 26 are
All hold.

Therefore, when V _O = 0, a current is supplied to the bandgap circuit 3, and when V _O ≈1.2, a starter circuit 2 for shutting off the current supply to the bandgap circuit 3 is added. With the addition of the startup circuit 2, the initial state V when the power is turned on
_{When O} = 0, current is supplied and I ₁ ≠ 0. Then,
From Equation 25, V _O ≠ 0 (> 0), and the operation stable point (≈1.
Settles in 2V).

[0064]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an example of the configuration of a bandgap type constant voltage generating circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram more specifically illustrating a part of the configuration. Is. Note that, in FIG. 2, the components having the same reference numerals as those in FIG. 1 have the same functions.

The bandgap type constant voltage generating circuit of this embodiment has a structure in which the current inverting amplifier 1 and the starting circuit 2 are provided between the bandgap circuit 3 and the power supply (V _cc ).

The power supply terminal 1c of the current inverting amplifier 1 and the power supply terminal 2c of the starting circuit 2 are connected to the power supply _Vcc, and the reference power terminal 2a of the starting circuit 2 is connected to the reference potential E ₀ . Input terminal 1a of the current inverting amplifier 1
Is connected to the collector of the transistor Q ₃ , and the output terminal 1b of the current inverting amplifier 1 and the starting voltage terminal 2b of the starting circuit 2 are connected to the output voltage terminal (V _O ).

Q ₁ and Q forming the band gap circuit 3
₃ is a transistor having the same shape, Q ₂ is a transistor having an emitter area N times as large as Q ₁ , and R ₁ and R ₂ are resistors having the same resistance value.

[0069]

[Equation 27]

[0070]

[Equation 28]

[0071]

[Equation 29]

The current inverting amplifier 1 is composed of PNP transistors Q ₄ , Q ₅ and Q ₆ having the same shape. Therefore, in Equation 24, M = 2 (the following equation).

[0073]

[Equation 30]

The start-up circuit 2 is composed of diodes D ₁ , D ₂ , D ₃ and a resistor R ₄ of the same shape. In the starting circuit 2, when the output voltage V _O = 0, D ₁ is conductive, D ₂ and D ₃ are non-conductive, and the power supply V _cc changes to R ₄ and D _1.
A current is supplied to R ₁ and Q ₁ via. Output voltage V _O
In the vicinity of 1.2 V, D ₂ and D ₃ are conductive and D ₁ is non-conductive, so that no current is supplied from the starting circuit 2 to the bandgap circuit 3 and the current inverting amplifier 1.

At the output stable point, from the relationships of the equations 25, 26 and 2,

[0076]

[Equation 31]

When the relationship of equations 29 and 30 is substituted into equation 31,

[0078]

[Equation 32]

It becomes

The relationship between I ₁ and I ₃ is obtained from the equation 32. If I ₁ > I ₃ , the left side> 0 and the right side <0 of the equation 32 are obtained.
If I ₁ <I ₃ , conversely, the left side is <0 and the right side is> 0. That is, the relationship of I ₁ = I ₃ is derived from the equation 32. Therefore, the following relationship holds from the equation (30).

[0081]

[Expression 33]

From the relationships of the equations 23, 28, 33 and 2, the output voltage V _O is given by the following equation.

[0083]

[Equation 34]

From the equations 26 and 34, the current I ₂ (= I ₁ = I
₃ ) is determined as follows.

[0085]

[Equation 35]

That is, with the circuit configuration of this embodiment illustrated in FIGS. 1 and 2, the transistors Q ₁ , Q ₂ , and Q are formed.
The current of ₃ does not depend on the power supply V _cc at all, and the resistance value of the resistor R ₃ which is a constant determined from the circuit configuration and the transistor Q ₂
And the emitter area ratio N of Q ₁ and the temperature T alone.

That is, it is possible to reduce the influence of the fluctuation of the power supply voltage V _cc on the output voltage V _O , and by using the low gain current inverting amplifier 1 and the starting circuit 2 having a simple structure, It does not cause the circuit configuration to be complicated as in the case of using a high-gain differential amplifier or the like, and the design from being complicated due to consideration of phase compensation.

[0088]

According to the bandgap type constant voltage generating circuit of the present invention, it is possible to reduce the influence of fluctuations in the power supply voltage on the output voltage with a relatively simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of the configuration of a bandgap constant voltage generating circuit that is an embodiment of the present invention.

FIG. 2 is a circuit diagram more specifically illustrating a part of the configuration thereof.

FIG. 3 is a circuit diagram showing an example of a configuration of a conventional bandgap type constant voltage generating circuit.

FIG. 4 is a circuit diagram showing an example of a configuration of a conventional bandgap type constant voltage generating circuit.

[Explanation of symbols]

1 ... current inverting amplifier, 1a ... input terminal, 1b ... output terminal, 1c ... power supply terminal, Q ₄ to Q ₆ ... transistors,
2 ... starting circuit, 2a ... reference power supply terminal, 2b ... starting voltage terminal, 2c ... power supply terminal, D ₁ to D ₃ ... diodes, R
₄ ... resistors, 3 ... bandgap circuit, Q ₁ to Q ₃ ... transistor (first to third transistors), R ₁ to R ₃ ...
Resistance (first to third resistance), _Vcc ... Supply power (voltage),
_VO ... Output voltage (terminal)

Claims (1)

[Claims] 1. The collector and base of the first transistor are connected to the first terminal of the first resistor and the base of the second transistor, and the emitter of the first transistor and the emitter of the third transistor are at a reference potential. Connected to the
The collector of the second transistor is the first of the second resistor.
A terminal and a base of the third transistor, an emitter of the second transistor is connected to a first terminal of a third resistor, a second terminal of the third resistor is connected to a reference potential, and A second terminal of the first resistor and a second terminal of the second resistor are bandgap constant voltage generating circuits connected to a voltage output terminal, and a current inversion having an input terminal, an output terminal and a power supply terminal. An amplifier, a starting circuit having a power supply terminal, a reference power supply terminal and a starting voltage terminal,
The power supply terminal of the current inverting amplifier and the power supply terminal of the starting circuit are connected to a power supply, the reference power terminal of the starting circuit is connected to the reference potential, and the input terminal of the current inverting amplifier A bandgap constant voltage generating circuit, wherein the collector of the third transistor is connected, and the output terminal of the current inverting amplifier and the starting voltage terminal of the starting circuit are connected to the voltage output terminal. .