JPS5897797A - Voltage-current conversion circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention applies pulses of voltage swinging to the positive and negative sides with respect to a reference level of ground potential as an input signal, and the current waveform outputted by an amplifier This invention relates to a voltage/current conversion circuit that produces an output with a symmetrical current waveform.

A conventional example will be explained using FIG. Operational amplifier (
A non-inverting input terminal + of an operational amplifier (hereinafter referred to as an operational amplifier) 7 is connected to a ground potential 100 via a bias resistor 5.

The inverting input terminal of this operational amplifier 7 and the signal input terminal 12
An impedance element 4 is connected between them, and a feedback impedance element 6 is further connected to the connection point between the inverting input terminal of the operational amplifier 7 and the impedance element 4. The other end of the feedback impedance element 6 is connected to a connection point where the emitters of the transistors 1.2 and the collector of the transistor 3 are commonly connected, and further connected to the impedance element 8. The other end of impedance element 8 is connected to ground potential 100. The collector of transistor 2 is connected to output terminal 10, and the base is connected to the output terminal of operational amplifier 7 and transistor 1.
, connect to the base of 2. Transistor 1 is stock type Pf'
JP) Multi-collector structure of transistors, the first collector is connected to the output terminal of operational amplifier 7 and transistors 1 and 2.
Connect to the connection point with the base. The second collector is connected to the base of transistor 3. Emi, Ri is output terminal 1
1 and the output current at the output terminal 10°11 is expressed by the following formula when there is a strong input, so ■. =(■.-VB
I2)/Rs・・・・・・・・・・・・・・・・・・
・ (1) I,, = (V0+Vag1) /R,...
・・・・・・・・・・・・・・・・・・ (2) Here l,
. : Current value flowing out from the output terminal, stone: Current value flowing in from the output terminal, voltage value of the dynamic range of the output in v0 operational amplifier 7, VBE2) Pace emitter of transistor 2, voltage across the gate, VBICI) Voltage of transistor 1 Base-emitter voltage, 几. Impedance element 8
The value of the voltage corrected so that the above output current values are equal.
In the current conversion circuit, for transistor 2Of7,
Since transistor 1 is a lateral PNP transistor, fT of the composite transistor composed of transistor 1 and transistor 3 is determined by the hollow transistor 1 in its high frequency characteristics. Furthermore, since f7 of transistor 1 has current dependence as shown in Fig. 3, fT of the composite transistor composed of transistor 1 and transistor 3 also decreases in response to a small input signal, and when this composite transistor operates, operational amplifier 7 is This results in the inconvenience that the entire system including this becomes unstable.

The object of the present invention is to improve the above-mentioned drawbacks and provide a voltage/current conversion circuit that operates stably even with very small input signals.

According to the present invention, a first impedance element is connected between an inverting input terminal of an amplifier and a signal source, and a second impedance element is connected to a connection point between the first impedance element and the inverting input terminal of the amplifier. The other end of the second impedance element is connected to the respective emitters of second transistors having different conductivity types, each of which receives the output of the amplifier at its base. The collector of $1 is connected to the base of this second transistor, and the collector of @2 is connected to the base of a third transistor of the same conductivity type as the first transistor. Connect, 1st. The emitter of the second transistor, the tortoise, and the collector of the third transistor are commonly connected, and a third impedance element is connected between this common connection point and the ground potential,
A constant current source is connected to a common connection point between the second collector of the second transistor and the base of the third transistor, the collector of the first transistor is used as a first output terminal, and the third A voltage/current conversion circuit is obtained, characterized in that the emitters and iris of a transistor are used as second output terminals.

Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, and the same parts as in the conventional example shown in FIG. 1 are given the same reference numerals.

In the second section, a constant current circuit 9 is connected between the base of the transistor 3 and the second voltage supply section 102 . In other words, when the input signal is small, this transistor 1 does not exceed the current value drawn from the constant current circuit 9, so %'T
does not fall below a certain value, and the entire system including the operational amplifier 7 can be stabilized when the composite transistor consisting of the transistor 1 and the transistor 3 is operated. In particular, in the present invention, the current value of the constant current source 9 is smaller than 5, since the peak of the current amplification factor of the multi-collector transistor is at 100μ.
It is desirable to choose a value between μA and 50 μA.

Fig. 3 shows another embodiment of the present invention, and Fig. 1.2 shows another embodiment of the present invention.
The same parts as those in the figure are indicated by the same reference numerals.

A filter is constructed by connecting resistors 18.21 and capacitors 19.20 in series and parallel as impedance elements 4 and 6, and impedance element 5 is inserted for bias.
It is something that Resistance 24, 25.

26, a capacitor 27 is for phase compensation. Output terminal 1
A current mirror circuit consisting of transistors 11, 15, 14 and resistors 11, 12' connected to the output terminal 10 is a circuit that changes the direction of the current flowing to the output terminal 10 and supplies it to the output terminal 17. A voltage/current conversion circuit is configured in which a current converted according to the direction of the voltage inputted from the input terminal 12 is outputted to either of the output terminals 11 and 17.

This voltage/current conversion circuit operates as follows.

Current output 10 appearing on output terminal 10.11 during weak input
The e-work 11 is expressed by the following formula.

However, Z4: Impedance forming the impedance element 4 Z6: Impedance forming the impedance element 6 during strong input. , step 1, is expressed by the following equation.

However, vo: Dynamics of output in operational amplifier 7.

Therefore, the current value of the output terminal 10.11 is the dynamic value of the operational amplifier output, and if the voltage during operation is equal to the voltage during upper and lower amplification, then the current value of the output terminal 10.
It is determined by dividing the voltage that depends only on E by the value of resistance R. Further, even if an attenuator is inserted between the operational amplifier output and transistors 1 and 2, the relationship is the same. Furthermore, since it is also possible to make a fist in which the impedance elements 4 and 6 have frequency characteristics, they are superimposed on the input signal. It is possible to develop a system that can remove noise and wow-pull components.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example. FIG. 2 is a circuit diagram showing one embodiment of the present invention. FIG. 3 is a graph showing the current dependence of fT in a type 1 PNP. FIG. 4 is a circuit diagram showing another embodiment of the present invention. 1.2, 3, 13, 14.15...Transistor, 7...Opean 7% 4#5-6-8...
...Impedance element, 9... Constant current source, 11.12'. 21.22, 23, 24, 25.26... Resistor, 19.20, 27... Capacitor, 100.
...Ground, 101...Positive voltage source,
102... Negative voltage source, 12... Input terminal, 10, 11.17... Output terminal. 1 @ Fig. 2 1) if ke / ρ ke Yukiho 9 Fig. 3

Claims (1)

[Claims] an amplifier having at least an inverting input terminal to which an input signal is applied; a first transistor of a first conductivity type whose base receives the output of the amplifier; and a transistor of a second conductivity type; and a third transistor of the first conductivity type whose base receives the collector output of the second transistor.
a transistor, means for commonly connecting the emitter of the first transistor, the emitter of the second transistor, and the collector of the third transistor, and an output signal obtained by the common connecting means. means for providing negative feedback to the amplifier; and means for applying current to a connection between the collector of the second transistor and the base of the third transistor; A voltage/current conversion circuit characterized by obtaining an output.