JPH0243232B2 - - Google Patents

Description

Detailed Description of the Invention The present invention applies voltage pulses that swing to the positive and negative sides with respect to a reference level such as ground potential as an input signal, so that the current waveform output by an amplifier is symmetrical with respect to the reference level. This invention relates to a voltage/current conversion circuit that obtains an output with a current waveform.

A conventional example will be explained using FIG. The non-inverting input terminal + of an operational amplifier (hereinafter referred to as an operational amplifier) 7 is connected to the ground potential 10 via a bias resistor 5.
Connected to 0. An impedance element 4 is connected between the inverting input terminal of this operational amplifier and the signal input terminal 12, and the inverting input terminal of the operational amplifier 7 is
A feedback impedance element 6 is further connected to the connection point between the impedance element 4 and the impedance element 4 . The other end of the feedback impedance element 6 is connected to a connection point through which the emitters of the transistors 1 and 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 the transistor 2 is connected to the output terminal 10, and the base is connected to the output terminal of the operational amplifier and the bases of the transistors 1 and 2. Transistor 1 has a multi-collector structure of a horizontal PNP transistor, and the first collector is connected to the connection point between the output end of the operational amplifier and the bases of transistors 1 and 2. The second collector is connected to the base of transistor 3. The emitter is connected to output terminal 11, and when there is strong input, output terminals 10 and 1
The output current at 1 is expressed by the following formula.

I ₁₀ = (V ₀ − V _BE2 )/R ₈ ………(1) I ₁₁ = (V ₀ + V _BE1 )/R ₈ ………(2) Here, I ₁₀ : Current value flowing out from the output terminal ,
I ₁₁ : Current value flowing from the output terminal, V ₀ : Voltage value of the output dynamic range in operational amplifier 7, V _BE2 : Voltage between base and emitter of transistor 2, V _BE1 : Voltage between base and emitter of transistor 1 , R _O : Value of impedance element 8.

In the voltage/current conversion circuit corrected so that the above output current values are equal, transistor 2
In contrast to f _T of the composite transistor consisting of transistor 1 and transistor 3, transistor 1 is a lateral PNP transistor, so the high frequency characteristics _are almost determined by transistor 1. Furthermore, since f _T of transistor 1 has current dependence as shown in Figure 3, f _T of the composite transistor consisting of transistor 1 and transistor 3 also decreases in response to a small input signal, and when this composite transistor operates, the operational amplifier This results in the inconvenience that the entire system including 7 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.

A feature of the present invention is that, as described above, the base emitter paths are connected in parallel between the output of the operational amplifier and the other end of the impedance element, one end of which is connected to a reference potential point. a third transistor having a base connected to the collector of the second transistor and a collector connected to the other end of the impedance element and having the same conductivity type as the first transistor; For a voltage/current conversion circuit having an output stage configuration in which outputs are obtained from the collector of a transistor and the emitter of a third transistor, a connection point between the collector of the second transistor and the base of the third transistor is used. This is because a constant current circuit is connected.

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 Figure 2, transistor 3
A constant current circuit 9 is connected to the base of the second voltage supply section 10.
Connect between 2 and 2. In other words, even when there is a small input signal, transistor 1 does not go below the current value drawn from constant current circuit 9, so f _T also does not go below a certain value, and transistors 1 and 3
The entire system including the operational amplifier 7 can be stabilized when the composite transistor consisting of the following is operated. In particular, in the present invention, since the current amplification factor of the multi-collector transistor has a peak of 100 .mu., the current value of the constant current source 9 is desirably selected to be smaller than 100 .mu.A.

FIG. 4 shows another embodiment of the present invention,
The same parts as in FIGS. 1 and 2 are designated by the same reference numerals. Resistors 18 as impedance elements 4 and 6,
21, a filter is constructed by direct and parallel connection of capacitors 19 and 20, and impedance element 5
is inserted for bias. resistance 24,
25, 26, and a capacitor 27 are for phase compensation. A transistor 13 connected to the output terminal 10,
15 and 14 and resistors 11 and 12' is a circuit that changes the direction of the current flowing through the output terminal 10 and supplies it to the output terminal 17. A voltage/current conversion circuit is configured in which a current converted depending on the direction of the voltage inputted from the output terminal 12 is outputted to either the output terminal 11 or 17.

This voltage/current conversion circuit operates as follows. At the time of weak input, the currents I ₁₀ and I _{11 appearing at the output terminals 10 and 11} are expressed by the following equations.

I ₁₁ = Z ₆ / Z ₄・V _IN ÷ R ₈ = I ₁₀ ………(3) However, Z ₄ : Impedance that constitutes impedance element 4 Z ₆ : Impedance that constitutes impedance element 6 I ₁₀ at the time of strong input , I ₁₁ is expressed by the following equation.

I ₁₀ = (V ₀ × R ₂₅ / R ₂₅ + R ₂₄ − V _BE2 ) / R ₈ ………(4) I ₁₁ = (V ₀ × R ₂₅ / R ₂₅ + R ₂₄ + V _BE1 ) / R ₈ ……… (5) However, V ₀ : Voltage during dynamic operation of the output of operational amplifier 7. Therefore, the current values of output terminals 10 and 11 are equal to each other when the voltages of the operational amplifier output during dynamic operation are equal during upper and lower amplification. The voltage that depends only on one V _BE of transistors 1 and 2 that performs
Determined by dividing by the value of _R8 . 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 possible to give the impedance elements 4 and 6 a frequency characteristic, the frequency characteristics are added to the input signal. It is possible to develop a system that can remove noise and ripple 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 f _T in a horizontal PNP. FIG. 4 is a circuit diagram showing another embodiment of the present invention. 1, 2, 3, 13, 14, 15... transistor, 7... operational amplifier, 4, 5, 6, 8... impedance element, 9... constant current source, 11, 12',
21, 22, 23, 24, 25, 26...resistance,
19, 20, 27... Capacitor, 100... Ground, 101... Positive voltage source, 102... Negative voltage source, 12... Input terminal, 10, 11, 17...
...Output terminal.

Claims (1)

[Claims] 1 an amplifier to which an input signal is applied to an inverting input terminal; a first transistor of a first conductivity type and a second transistor of a second conductivity type; and a collector of the second transistor; A third transistor of the first conductivity type whose base is connected, the emitters of the first and second transistors, and the collector of the third transistor are commonly coupled, and a signal obtained at the common coupling point is sent to the amplifier. means for negative feedback; an impedance element connected between the common coupling point and the reference potential point; and means for applying a constant current to a connection between the collector of the second transistor and the base of the third transistor. and obtains an output from both the collector of the first transistor and the emitter of the third transistor.
Current conversion circuit.