JP2567869B2 - Voltage / current conversion circuit - Google Patents

Description

The present invention relates to a voltage / current conversion circuit, and is applicable to, for example, a horizontal deflection circuit.

[Prior Art] In a conventional horizontal deflection circuit composed of an integrated circuit, a horizontal synchronizing frequency is converted into a voltage signal and then converted into a current signal to control the horizontal oscillation circuit.

A conventional voltage / current conversion circuit used in this way is shown in FIG.

In FIG. 2, the input voltage signal V1 is the one transistor of the differential amplifier circuit 2 driven by the constant current circuit 1.
A comparison operation is performed with the voltage signal V2 applied to the base of Q1 and applied to the base of the other transistor Q2.

The collector of the transistor Q1 is connected to the collector of the transistor Q3 whose emitter is connected to the power supply line L1 via the resistor R1, and the collector of the other transistor Q2 is connected to the power supply line L1 whose emitter is connected to the power supply line L1. It is connected to the collector of transistor Q4. The bases of these transistors Q3 and Q4 are transistor Q1
Of the current mirror circuit 3 is thus connected.

The collector voltage signal of the transistor Q2 obtained based on the above-mentioned comparison result is input to the emitter follower circuit 4 which is a Darlington connection of the transistors Q5 and Q6, and the output voltage V2 of this emitter follower circuit 4 is the above-mentioned transistor Q2. It is designed to be fed back to the base.

Thus, the differential amplifier circuit 2, the current mirror circuit 3, and the emitter follower circuit 4 make up the voltage follower circuit 5.
Is configured to obtain the voltage signal V2 following the input voltage signal V1 at the output terminal of the emitter follower circuit 4.

The output end of the emitter follower circuit 4 is grounded via an external variable resistor VR so that a current signal I1 corresponding to the output voltage signal V2 flows. The current signal I1 obtained in this way is applied to the transistors Q7 to Q9 provided on the collector side of the transistor Q6 of the emitter follower circuit 4.
Is supplied as a control signal to the horizontal oscillation circuit via the current mirror circuit 6 configured by.

[Problems to be Solved by the Invention] By the way, according to the above-described conventional circuit, the input voltage signal V1
The voltage signal I1 obtained by converting the current signal V2 that follows the variable resistance VR by the variable resistor VR does not directly become the output current signal. That is, the output current from the current mirror circuit 6 is the current signal I1 thus obtained plus the base current I2 of the transistor Q2 and has an offset. Therefore, even if the input voltage signal V1 is doubled, the current I1 is doubled, but the total output current I1 + I2 is not doubled due to the offset. Therefore, this output current I1
If you try to control the horizontal oscillation circuit by + I2, a tracking error will occur.

Moreover, this offset current (base current) I2 is not fixed, and the current amplification factor h of the transistor Q2 is h.
It is difficult to stabilize because it changes depending on _FEQ2 and temperature characteristics.

Therefore, the pair of transistors Q1 of the differential amplifier circuit 2
It is conceivable to connect each Q2 in Darlington connection to reduce the base current to suppress the influence of this offset current, but to reduce the dynamic range or offset the differential input voltage and the voltage actually compared. May occur and is not practically applicable.

The present invention has been made in consideration of the above points, and an object thereof is to provide a voltage / current conversion circuit capable of converting a voltage signal into a current signal without having an offset.

[Means for Solving the Problems] In order to solve the problems, according to the present invention, a differential amplifier circuit for comparing an input voltage signal with an output voltage signal of an emitter follower circuit and an emitter for inputting a comparison output thereof. A voltage provided with a voltage follower circuit consisting of a follower circuit, a resistance element for converting the output voltage signal of the emitter follower circuit into a current signal, and an output circuit for supplying the current signal flowing into the emitter follower circuit to the next stage circuit. In the current conversion circuit, a compensation transistor that allows the same base current as the base current of the transistor in the differential amplifier circuit to which the output voltage signal of the emitter follower circuit is fed back is provided, and the base current of the compensation transistor is used as the emitter follower circuit. The current signal that has been subtracted from the current signal flowing in I tried to pay.

[Operation] A voltage signal corresponding to the input voltage signal obtained through the voltage follower circuit composed of the differential amplifier circuit and the emitter follower circuit is converted into a current signal by the resistance element and output through the output circuit. At this time, the output current signal is the current signal from the resistance element plus the base current of one of the transistors of the differential amplifier circuit, and this base current serves as an offset.

Therefore, the compensating transistor forms a current signal that is the same as the base current of one transistor of the differential amplifier circuit, and this current signal cancels the base current component of one transistor of the differential amplifier circuit to cancel the current signal by the resistance element. I tried to output only.

As a result, it is possible to obtain an output current signal that does not have an offset corresponding to the input voltage signal.

[Embodiment] An embodiment of the present invention will be described in detail below with reference to FIG. 1 in which parts corresponding to those in FIG.

In the voltage / current conversion circuit of this embodiment, the transistor Q2 included in the output current signal in the conventional circuit is used.
A compensating circuit 10 for canceling the base current component is provided. The compensation circuit 10 is provided with the same base voltage as that of the transistor Q11 of the constant current circuit 1, and includes a transistor Q12 that flows a constant current I0 that is half that of the transistor Q11.
With 1. The emitter of the base current compensation transistor Q13 whose collector is connected to the power supply line L1 is connected to this constant current circuit 11, and the base current determined by this constant current I0 and the current amplification factor h _FEQ13 of this transistor.
I3 (= I0 / h _FEQ13 ) flows.

This base current I3 passes through the current mirror circuit 12 composed of the transistors Q14 and Q15 and the emitter follower circuit 4
It is designed to be leaked to.

Assuming that the current determined by the variable resistor VR is I1 and the base current of the transistor Q2 is I2 as described above, these sum currents I1 + I2 flow in the emitter follower circuit 4, and
Since the current I3 is flown in by the current mirror circuit 12, the current I1 + I2-I3 flows through the transistor Q7, and the output current I OUT becomes I1 + I2-I3.

In the above configuration, when the input voltage signal V1 is stable, the same collector current I0 flows through both transistors Q1 and Q2 of the differential amplifier circuit 3. Therefore, the base current I2 of the transistor Q2 at this time is a value (I0 / h _FEQ2 ) determined by the current I0 and the current amplification factor h _FEQ2 .

Therefore, the output current I OUT becomes as shown in the following formula I OUT = I1 + I2-I3 = I1 + (I0 / h _FEQ2 )-(I0 / h _FEQ13 ) (1).

Here, since the current amplification factors h _FEQ2 and h _FEQ13 of the transistors Q2 and Q13 are formed on the same integrated circuit,
They are almost the same and have similar temperature characteristics.

 Therefore, from the above formula (1), the output current I OUT is determined by the variable resistance VR as shown in the following formula I OUT = I1 (2).

Thus, according to the embodiment described above, the input voltage signal V1
Can be converted into an output current signal I OUT having no offset component. Therefore, even when applied to a horizontal deflection circuit, it is possible to obtain an oscillation signal without causing a tracking error.

Although the present invention is applied to the horizontal deflection circuit in the above embodiment, the present invention is not limited to this.
It can be applied to various circuits having a voltage / current conversion circuit.

[Effects of the Invention] As described above, according to the present invention, a compensating transistor that allows a base current equal to the base current of one transistor of the voltage follower circuit to flow is provided, and the base current of this compensating transistor is set to the output current. Since the base current component of one transistor is added so as to be canceled, a voltage / current conversion circuit capable of converting an input voltage signal into an output current signal without having an offset component can be obtained.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of a voltage / current conversion circuit according to the present invention, and FIG. 2 is a connection diagram showing a conventional circuit. 2 ... Differential amplifier circuit, 4 ... Emitter follower circuit, 5
...... Voltage follower circuit, 6 …… Current mirror circuit, 10
... Compensation circuit, Q12 ... Compensation transistor, VR ... Variable resistance.

Claims (1)

(57) [Claims] 1. A voltage follower circuit comprising a differential amplifier circuit for comparing an input voltage signal with an output voltage signal of an emitter follower circuit and the emitter follower circuit for inputting a comparison output thereof, and an output voltage of the emitter follower circuit. In a voltage / current conversion circuit comprising a resistance element for converting a signal into a current signal and an output circuit for supplying a current signal flowing into the emitter follower circuit to a circuit in the next stage, the output voltage signal of the emitter follower circuit is A compensation transistor that supplies the same base current as the base current of the transistor in the differential amplifier circuit that is fed back is provided, and the base current of the compensation transistor is subtracted from the current signal flowing into the emitter follower circuit, and the resistance element is used. It is characterized in that the converted current signal is supplied to the circuit of the next stage. Voltage / current converting circuit.