JPH04313902A - Current voltage conversion circuit - Google Patents

Abstract

PURPOSE:To obtain the current voltage conversion circuit which is hardly oscillated. CONSTITUTION:Transistors(TRs) Q4 and Q5 form a differential amplifier pair. A collector potential of the TR Q4 is subject to buffer operation by the TR Q6 and the result to one input of an amplifier circuit 2. A collector potential of the TR Q5 is subject to buffer operation by a TR Q7 and the result to the other input of the amplifier circuit 2. The amplifier circuit 2 amplifies the potential given to both the inputs in a differential amplifier form. Since the signal is delivered in the differential form, a leakage signal is not amplified and the oscillation is hardly caused.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-voltage conversion circuit formed on a single chip used in optical communication ICs, and more particularly to a current-voltage conversion circuit that is difficult to oscillate.

0002

2. Description of the Related Art FIG. 3 is a circuit diagram of a conventional current-voltage conversion circuit of this type. In the figure, 1 is a photodiode whose cathode is connected to a power supply Vcc. Q1 is an NPN transistor, and has a base connected to the anode of the photodiode 1, an emitter connected to GND, and a collector connected to the power supply Vcc via a resistor R1.

Q2 is an NPN transistor whose collector is connected to the power supply Vcc through a resistor R2, whose emitter is connected to GND through a diode D1 and a resistor R3, and whose base is connected to the collector of the transistor Q1. A common connection point between resistor R3 and diode D1 is connected to the base of transistor Q1 via resistor R4.

Q3 is an NPN transistor whose collector is connected to the power supply Vcc via a resistor R5 and whose emitter is connected to a resistor R.
6 to GND, and its base is connected to the collector of transistor Q3. The amplifier circuit 2 has a single-ended input, and the amplifier circuit 2 amplifies and outputs the potential of the collector of the transistor Q3.

Next, the operation will be explained. Photodiode 1 converts the irradiated light into current and supplies it to the base of transistor Q1. Transistor Q1 amplifies the current and applies it to resistor R1. Resistor R1 converts the current from transistor Q1 into a voltage. When the current flowing through transistor Q1 increases, the base potential of transistor Q2 decreases. This drop is caused by transistor Q2, diode D1, and resistor R4.
is fed back to the base of the transistor Q1 via the transistor Q1, the base potential of the transistor Q1 decreases, and the current flowing through the transistor Q1 decreases. In this way, transistor Q
1, Q2, diode D1, and R4 form a negative feedback loop.

If the current flowing through the resistor R4 is I, and the resistance value of the resistor R4 is R, the voltage V generated across the resistor R4 is I.
×R. The current I depends on the current flowing through the photodiode 1. In other words, the current generated by the photodiode 1 is converted into a voltage V by the negative feedback loop. This voltage V is amplified by transistors Q2 and Q3, further amplified by an amplifier circuit 2, and output. In other words, the current flowing through the photodiode 1 is converted into voltage and amplified.

The current-voltage conversion circuit shown above has a power of several hundred MH
It has a high gain of several tens of dB in the z band.

[0008]

[Problems to be Solved by the Invention] The conventional current-voltage conversion circuit is configured as described above and is formed on one chip, and has a high gain and a wide band. The problem is that a positive feedback loop is formed in which the signal returns through the circuit, etc., and is amplified again, making it easy to oscillate.

The present invention has been made to solve the above-mentioned problems, and its object is to obtain a current-voltage conversion circuit that is less likely to oscillate.

0010

SUMMARY OF THE INVENTION The present invention is applied to a current-voltage conversion circuit formed on one chip and converting input current into voltage.

The current-voltage conversion circuit according to the present invention includes a first transistor to which the input current is applied to a control electrode, a reference voltage to the control electrode, and one electrode to which the input current is applied.
a second transistor connected to one electrode of the transistor and forming a differential pair with the first transistor; and one input having the potential of the other electrode of the first transistor;
The potentials of the other electrodes of the second transistors are respectively input to the other inputs, and an amplifier circuit is provided which amplifies these potentials in a differential format.

0012

[Operation] In the present invention, a differential pair is formed by a first transistor whose control electrode is supplied with an input current and a second transistor whose control electrode is supplied with a reference voltage, and the amplifier circuit is connected to the first transistor. , the potentials of the other electrodes of the second transistors are amplified in a differential format, and signals are transmitted in a differential format, so even if a leakage signal is input, it is not amplified.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an embodiment of a current-voltage conversion circuit according to the present invention. Transistors Q4 and Q5 are NPN transistors forming a differential pair. The transistor Q4 has a base connected to the power supply Vcc via the photodiode 1, and a collector connected to the power supply Vcc via the resistor R7. The transistor Q5 has its base connected to GND via a reference voltage VB, its collector connected to the power supply Vcc via a resistor R8, and its emitter connected to the emitter of the transistor Q4. A common connection point between the emitter of the transistor Q4 and the emitter of the transistor Q5 is connected to GND via a constant current source 10.

The NPN transistor Q6 has its base connected to the collector of the transistor Q4, its collector connected to the power supply Vcc, and its emitter connected to GND through the constant current source 20 and connected to the transistor Q4 through the resistor R9.
It is also connected to the base of. NPN transistor Q7
The base is connected to the collector of the transistor Q5, the collector is connected to the power supply Vcc, and the emitter is connected to GN through the constant current source 30.
D, respectively. One input of the amplifier circuit 2 receives a potential obtained by buffering the collector potential of the transistor Q4 with the transistor Q6, and the other input receives the potential obtained by buffering the collector potential of the transistor Q4 with the transistor Q6.
A potential obtained by buffering the collector potential of No. 5 by transistor Q7 is input. The amplifier circuit 2 has a double-ended input and amplifies these potentials in a differential format.

The photodiode 1 converts the irradiated light into a current and inputs it to the base of the transistor Q4. Transistor Q4 causes a current corresponding to the base current to flow through resistor R7. When the current flowing through transistor Q4 increases, transistor Q
6's base potential decreases. This drop is caused by transistor Q6
, is fed back to the base of the transistor Q4 via the resistor R9, and the base potential of the transistor Q4 decreases, so that the current flowing through the transistor Q4 decreases. In this way, a negative feedback loop is formed by transistors Q4, Q6 and resistor R9.

A current Ia flows through the resistor R9 in accordance with the current generated by the photodiode 1, and is converted into a voltage across the resistor R9 by the negative feedback loop as in the circuit of FIG. This voltage is amplified by a differential pair consisting of transistor Q4 and transistor Q5, and is derived from the collectors of transistor Q4 and transistor Q5 as signals of opposite polarity. The collector potential of the transistor Q4 is buffered by the transistor Q6 and is input to one input of the amplifier circuit 2, and the collector potential of the transistor Q5 is buffered by the transistor Q6.
7 and input to the other input of the amplifier circuit 2, respectively. The amplifier circuit 2 amplifies the difference voltage between these voltages.

As shown above, since signals are transmitted in a differential format, the output of the amplifier circuit 2 is grounded,
Even if it returns via the power supply Vcc, it acts as a common mode signal, and for example, the base potential of transistor Q4, which is one input of a differential pair, and the transistor Q, which is the other input, of a differential pair.
The difference with the base potential of 5 is kept constant. Therefore, there is no positive feedback loop as in the conventional case, making it difficult to oscillate. In addition, transistors Q6 and Q, which are emitter followers,
Since the bias current of 7 and the bias current of the differential pair consisting of transistors Q4 and Q5 were supplied from a constant current source,
The configuration is such that the signal current does not flow through the ground, so that even if a leakage signal is input to the emitter of the transistor Q6, for example, it will not affect the ground and is strong against oscillations that occur via the ground.

Note that the constant current source 10 shown in the above embodiment,
20 and 30, each resistor R10 as shown in FIG.
, R20, and R30 may be provided. Further, even if the polarities of the transistors Q4, Q5, Q6, Q7, photodiode 1, and power supply shown in the above embodiment are reversed, the same effect as in the above embodiment can be obtained.

[0019]

As described above, according to the present invention, a differential pair is formed by the first transistor whose control electrode is supplied with an input current and the second transistor whose control electrode is supplied with a reference voltage. However, since the amplifier circuit amplifies the potential of the other electrode of the first and second transistors in a differential format and transmits signals in a differential format, leakage signals are not amplified. do not have. As a result, there is an effect that oscillation is difficult to occur.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a current-voltage conversion circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the current-voltage conversion circuit according to the present invention.

FIG. 3 is a circuit diagram showing a conventional current-voltage conversion circuit.

[Explanation of symbols]

2 Amplifier circuit Q4, Q5 NPN transistor

Claims (1)

[Claims] 1. A current-voltage conversion circuit formed on one chip and converting an input current into a voltage, the circuit comprising: a first transistor to which the input current is applied to a control electrode; and a reference voltage to the control electrode. , a second transistor having one electrode connected to one electrode of the first transistor and forming a differential pair with the first transistor; 1. A current-voltage conversion circuit comprising an amplifier circuit to which the potentials of the other electrodes of the second transistors are respectively input, and which amplify these potentials in a differential format.