JPH0195610A - voltage buffer circuit - Google Patents

Abstract

PURPOSE:To constitute a voltage buffer circuit with high accuracy with a few element number by making each output current of an input/output transistor(TR) equal to each other at an times. CONSTITUTION:An input TR Q1 is connected to an output TR Q2 so that the output from the TR Q1 is given to the TR Q2. Then a means operating the input TR Q1 and the output TR Q2 so as to have an identical current at all times is provided. Since the operating current of both the TRs Q1, Q2 is made always identical in this way, the error voltage is independent of the output voltage and the input/output voltage error is decreased. Thus, a voltage buffer circuit with a few element number and high accuracy is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage buffer circuit having high human power impedance and low output impedance characteristics suitable for IC implementation.

[Prior Art J] A voltage follower circuit using an operational amplifier (OPA) is normally used as a voltage buffer circuit, as shown in FIG.

Although this circuit has excellent characteristics such as high human power impedance, low output impedance, and little input/output voltage error, when integrated into an IC, it requires an operational amplifier circuit, so it takes up a large area. There is a drawback. In particular, since the voltage follower circuit is used with full feedback, it is necessary to increase the value of the internal capacitor for oscillation prevention, which is also disadvantageous in terms of the area of the IC. Therefore, in a voltage buffer circuit whose accuracy is not high enough to require the use of an operational amplifier, a circuit that can be configured with a small number of elements is desired.

In such a case, a voltage buffer circuit as shown in FIG. 3 can be considered from the prior art. Here, Ql is an input side PNP transistor that receives human power v1 as a base,
R1 is its load resistance. Transistor q2 is connected in cascade with transistor Q1, and the collector output of transistor Q1 is supplied to the output side NIN)--to the base of transistor Q2. Transistor Q2 connects load resistor R2 in the form of an emitter follower, and outputs V from its emitter. Take out. VCC is a power supply voltage.

Here, the output voltage V. is the following formula.

Vo=V++ (VBEI VBE2)
(1) v1□ and VBE2 are the base-emitter voltages of transistors Q1 and Ql, respectively.

(In equation 11, the value in parentheses is the error voltage. Here,
VBE□ and VBE2 are expressed by the following equations.

Here, ”-thermal i pressure (T-300°k te 26 mV) I1・
. . . emitter current of transistor Ql, I2 . . . collector current of transistor q2, ISl+IS2 . . . emitter base junction reverse saturation current. Therefore, what is in parentheses in equation (1) is as follows.

[Problems to be solved by the invention] I+ and 12 in equation (4) change significantly depending on the input side terminal v1, so the input/output voltage error also changes greatly depending on the input side terminal, and depending on the application. may not be available.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the conventional circuit and provide a voltage buffer circuit with a small number of elements and high accuracy.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a voltage buffer circuit configured by connecting an output from an input transistor to an output transistor. The present invention is characterized in that a means is provided between the side transistor and the output side transistor to cause the input side transistor and the output side transistor to always operate at the same current value.

[Function 1] In the present invention, in the circuit shown in FIG. 3, the operating currents of both transistors are always equal, so the error voltage shown in equation (4) does not depend on the output voltage, and therefore It is possible to reduce voltage errors and realize a voltage buffer circuit with improved accuracy.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

An embodiment of the present invention is shown in FIG. In FIG. 1, the same parts as in FIG. 3 are given the same reference numerals.

In FIG. 1, Q3 is a PNP transistor for starting, and a resistor R3 is connected between its emitter and power supply voltage VCC.
, the collector is grounded, and the base is connected to the transistor q
It is connected to the connection point between the emitter of transistor Q1 and the base of transistor Q2. The value of the resistor R3 is set so that a slight base current flows through the transistor Q3. This small base current activates transistor q2.

Q4 and Q5 are PNPs forming a current mirror circuit.
It is a transistor, and each emitter is connected to the power supply voltage VCC. Both bases are connected in common, and the common connection point is connected to the collector of transistor Q5. The collector of transistor Q4 is connected to the emitter of transistor Ql. The collector of transistor Q5 is connected to transistor q2.
Connect to the collector of

Since transistors Q4 and Q5 constitute a current mirror circuit, the emitter current of transistor Q1 and the collector current of transistor Q2 are always equal. Therefore,
When the output voltage v0 of the transistor Q2 changes and the output current of this transistor Q2 changes, the transistor Q
Since the current value of 1 changes in the same way, the error voltage does not depend on the output voltage, as seen from equation (4), and therefore,
Accuracy is improved because the input/output voltage error is reduced.

Note that the present invention is not limited to the above-described embodiments; for example, the conductivity type of each transistor may be PNP or N.
Even if the polarity of the power supply voltage is reversed with respect to PN and the polarity of the power supply voltage is made negative, a voltage buffer circuit can be constructed in the same way.

[Effects of the Invention] As is clear from the above, according to the present invention, since the output currents of the input and output transistors are always equal, it is possible to configure a highly accurate voltage buffer circuit with a small number of elements. Therefore, compared to the case where an operational amplifier is used, there is an advantage that the chip area when integrated into an IC can be significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing an example of a normal voltage buffer circuit using an operational amplifier, and Fig. 3 is another example of a voltage buffer circuit according to the prior art. FIG. Ql...Input side transistor, Ql...Output side transistor, Q3...Starting transistor, Q4. Q5...Transistor for current mirror circuit,
R1, R2...Load resistance, R3...Resistor, VCC...Power supply voltage. λ (Yu Goro Mon/Tuesday - Hiroshi Eun I row's turn betting diagram Figure 1 Figure 9 coins gift money crystal 1 winter use - Kota term 1st room Oe million 9 mabufa turn 40 times Reto diagram Figure 2 I Mi → (Hard 1 d) Gyre Kidney Cause Figure 3

Claims (1)

[Claims] In a voltage buffer circuit configured by connecting an output from an input transistor to an output transistor, the input transistor and the output transistor are always connected between the input transistor and the output transistor. A voltage buffer circuit characterized in that it is provided with means for operating at mutually equal current values.