JP3107590B2 - Current polarity conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current polarity conversion circuit in an electronic circuit.

[0002]

2. Description of the Related Art In electronic equipment, a current polarity conversion circuit is often used.

FIG. 3 shows a conventional example of a current polarity conversion circuit. The current input terminal 31 is connected to the npn transistor Q1
And the emitter of the pnp transistor Q2. The base of the transistor Q1 is n
The base of the pn transistor Q3 is connected to the base and the collector of the pn transistor Q3.
4 are connected to the base and collector. The bias power supply VBB is commonly used for the emitters of the transistors Q3 and Q4.
Is connected, and the collector of the transistor Q3 is connected to the current source I1.
Is connected to the power supply Vcc line through the transistor Q4.
Is connected to the ground potential GND line via the current source I2.

The collector of the transistor Q1 is connected to the power supply VBB
The collector of the transistor Q2 is connected to the current input terminal of the current mirror circuit 32 connected to the line, and the current mirror circuit 33 connected to the ground potential GND line.
Is connected to the current input terminal of The current output terminals of the current mirror circuits 32 and 33 are commonly connected to a current output terminal 34.

Now, two current mirror circuits 32 and 33
Has an input / output current ratio of 1: 1 and two current sources I1,
It is assumed that the current of I2 is I, and a current of + i flows into the current input terminal 31. Then, due to the diode characteristics of the transistors Q1 to Q4, the collector current of Q1 becomes I, Q2
Is I + i, and at the output terminal 34, i
Current is drawn. Conversely, the input terminal 33
When a current of -i flows through the output terminal 34, a current of + i flows out of the output terminal 34. That is, the above circuit outputs the current with its polarity inverted.

The main current polarity conversion circuit is used, for example, in a resistance matrix circuit for converting a luminance / color difference signal of a television system into a primary color signal as shown in FIG. In FIG. 4, VY is a luminance signal, VR-Y, VB-Y
Are color difference signals. These signals are superimposed on the DC bias voltage VBB and input to a matrix circuit including resistors R1 to R9. A current output IR corresponding to the R signal is obtained from the resistor R1, a current output IG corresponding to the G signal is obtained from the resistor R5, and a current output IB corresponding to the B signal is obtained from the resistor R9. These output currents are input to current polarity conversion circuits 41, 42, and 43, whose polarities are converted and output, and are supplied to predetermined electrodes of a picture tube.

[0007]

In the circuit shown in FIG. 3, the input impedance is the parallel impedance of the emitter impedance of transistor Q1 and the emitter impedance of Q2. This impedance is defined as Zi. If a circuit having an output voltage Vi with an impedance Z is connected to the input side of this circuit, the input current becomes V
i / (Z + Zi). For example, a circuit connection as shown in FIG.

Here, when Z is sufficiently large with respect to Zi, there is no problem because the input impedance of the current polarity conversion circuit can be ignored. However, when Z is small, the input impedance of the current polarity conversion circuit cannot be ignored. However, there is a problem that a desired input current cannot be set. Here, the input impedance will be obtained by taking an example. First, the emitter impedance of the transistors Q1 and Q2 is KT /
(Q · I). K is the Boltzmann constant, T is the absolute temperature, and q is the charge of the electron.

Assuming that I = 0.1 mA, Q.sub.1 to Q.sub.4 have 0.
Since a current of 1 mA flows, each has an impedance of about 260 ohms at room temperature, and the input impedance of the current polarity conversion circuit is about 130 ohms. Therefore, if the input impedance of 130 ohm cannot be ignored, a desired output current cannot be obtained. There is also a disadvantage that the potential of the input terminal fluctuates due to the input impedance.

Further, the connection point between the emitters of the transistors Q3 and Q4 is grounded in FIG. 3, but it is often desired to actually bias it to a certain potential. In this case, a bias must be applied to a circuit or an element having a lower impedance than the emitter impedance of the transistors Q3 and Q4, the current flowing through Q3 and Q4 changes due to the diode characteristics, and the potential of the input terminal further changes. There is a problem that the desired output current cannot be obtained more and more easily.

Therefore, according to the present invention, the input impedance is reduced by applying feedback to the input terminal, the impedance is not affected by the impedance of the circuit connected to the input terminal, and the connection point of the transistor to which the input current is supplied is set to the impedance. It is an object of the present invention to provide a current polarity conversion circuit in which the potential fluctuation at the input terminal is extremely small and stable even when biased by a circuit or element having a high voltage.

[0012]

SUMMARY OF THE INVENTION The present invention comprises an emitter of a first transistor of a first polarity and a second transistor of a second polarity.
And the collector of the first transistor is connected to a current input terminal of a current mirror circuit of a first polarity, and the collector of the second transistor is connected to a current input terminal of a second polarity. A current polarity conversion circuit connected to a current input terminal of the mirror circuit, wherein the current output terminals of the first and second polarity current mirror circuits are commonly connected to an output terminal;

A third transistor whose base is connected to the base of the first transistor and whose collector is used as the first power supply directly or through a circuit; and a base and a collector connected to the base of the second transistor. A fourth transistor having an emitter connected to the emitter of the third transistor and having a collector connected to a second power supply directly or via a current source; an inverting input terminal connected to the input terminal; A high gain circuit having a positive phase input terminal connected thereto and an output terminal connected to bases of the first and third transistors.

[0014]

According to the above-mentioned means, the input terminal of the current polarity conversion circuit is subjected to negative feedback by the high gain circuit, thereby lowering the input impedance and stabilizing the potential of the input terminal.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The current input terminal 11 is connected to the emitter connection point A of the transistors Q1 and Q2 having different polarities. Transistor Q1
Is connected to the current input terminal of the current mirror circuit 12 connected to the first power supply Vcc line, and the collector of the transistor Q2 is connected to the second power supply GND line (ground line). It is connected to the current input terminal of the current mirror circuit 13. The current output terminals of the first and second current mirror circuits 12 and 13 are commonly connected to a current output terminal 15.

The base of transistor Q1 is connected to the base of transistor Q3, and the base of transistor Q2 is connected to the base and collector of transistor Q4. The collector of the transistor Q3 is the first power supply V
connected to the cc line, and the collector of the transistor Q4 is
It is connected to the second power supply GND line via the current source I1.

Further, a transistor Q is connected to the connection point A.
5 bases are connected. Transistors Q5 and Q6
Form a differential pair, and the emitters are commonly connected to a second power supply GND line via a current source I2. A constant bias VB is applied to the base of the transistor Q6, and the collector is connected to the current input terminal of the third current mirror circuit 14 connected to the third power supply Vcc line. The current output terminal of the current mirror circuit 14 is connected to the collector of the transistor Q5. The collector of the transistor Q5 is connected to the bases of the transistors Q1 and Q3.

Now, three current mirror circuits 12, 1
It is assumed that the input / output current ratio of the input terminals 3 and 14 is 1: 1 and a current of + i is supplied to the input terminal 11. Then, due to the diode characteristics of the transistors Q1 to Q4, the collector current of Q1 becomes I and the collector current of Q2 becomes I + i.
In 5, the current i is drawn. Conversely, when a current of −i is supplied to the input terminal 11, a current of + i is output from the output terminal 15. That is, the current polarity is converted and output.

In the above circuit, the transistors Q5,
Focusing on the differential pair formed by Q6, the third current mirror circuit 14, and the components of the transistor Q1, these circuits are high gain amplifiers having the input of the base of the transistor Q5 and the output of the emitter of the transistor Q1. is there. In this amplifier, the base of the transistor Q5 has a negative input, and the base of the transistor Q6 has a positive input. Here, since the base of the transistor Q5 and the emitter of the transistor Q1 are connected at the connection point A,
It can be seen as a voltage follower with a negative input and an output connected.

Therefore, negative feedback is applied so that the base potential of the transistor Q5 becomes equal to the potential applied to the base of the transistor Q6. As a result, the input impedance decreases. As a result, accurate current polarity conversion is obtained without the output current being affected by the impedance of the circuit connected to the input side.

Further, by the operation of the negative feedback, the potential of the input terminal hardly changes and a low impedance is maintained. Furthermore, since the base of the transistor Q6 has a high input impedance, the transistor Q6
The impedance of the circuit that biases 6 is
There is no need to carefully select low impedance ones. It can also be realized with a simple bias circuit using only a resistor. Thereby, the potential of the input terminal can be stabilized and set to a desired potential, and the current polarity conversion performance can be stably maintained.

FIG. 2 shows another embodiment of the present invention.
The same reference numerals are given to the parts common to. Input terminal 1
1 is connected to the inverting input terminal of the high gain amplifier 16. The positive phase input terminal of the high gain amplifier 16 is connected to a bias power supply V
Connected to B. The output terminal of the high gain amplifier 16 is connected to the bases of the transistors Q1 and Q3. Also in this embodiment, the same operation and effect as the circuit of FIG. 1 can be obtained.

In the above embodiment, the transistor Q3
Is directly connected to the first power supply, but may be connected via a circuit such as a current source. Although the collector of the transistor Q4 is connected to the second power supply via the current source, it may be connected directly.

[0025]

As described above, according to the circuit of the present invention, the input impedance is reduced by applying feedback to the input terminal, and the input current is not affected by the impedance of the circuit connected to the input terminal. Even if the connection point of the transistor to which is supplied is biased by a circuit or element having a high impedance, the potential fluctuation at the input terminal is extremely small and stable.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a diagram showing an example of a conventional current polarity conversion circuit.

FIG. 4 is a diagram showing a usage example of a current polarity conversion circuit.

[Explanation of symbols]

Q1 to Q6: transistors, 11: input terminals, 12 to 1
4 ... current mirror circuit, 15 ... output terminal, 16 ... high gain amplifier.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 1/56 H03F 3/45

Claims (1)

(57) [Claims] An emitter of a first transistor of a first polarity and an emitter of a second transistor of a second polarity are connected to an input terminal, and a collector of the first transistor has a first polarity. A current input terminal of a current mirror circuit, a collector of the second transistor is connected to a current input terminal of a current mirror circuit of a second polarity, and a current output of the current mirror circuit of the first and second polarities end, in current polarity conversion circuit connected to a common output terminal, the collector-base connected to the base of the first transistor is connected to a first power source without passing through the current source 3
And a fourth transistor having a base and a collector connected to a base of the second transistor, an emitter connected to an emitter of the third transistor, and a collector connected to a second power supply via a current source. A high gain circuit having an inverting input terminal connected to the input terminal, a positive phase input terminal connected to the bias source, and an output terminal connected to the bases of the first and third transistors. Characteristic current polarity conversion circuit.