JPH04207305A - Current/voltage conversion circuit - Google Patents

Abstract

PURPOSE:To obtain a current/voltage conversion circuit resistant for oscillation and a noise by providing a bias circuit provided with the same configuration as that of a circuit main body, and employing double-end input. CONSTITUTION:A current/voltage conversion circuit main body 30 is formed with the same configuration and the same arranged and wired circuit of circuit element as that of the bias circuit 40, and input is performed by a differential format setting the input of an AGC amplifier circuit 17 as double-end, therefore, the AGC amplifier circuit 17 can be also comprised of the differential format. Thereby, all the signals from input to output can be transmitted in the differential format. Therefore, the circuit configuration resistant for the oscillation due to the unrequired signal of common mode (in-phase signal), etc., can be formed. Thereby, an IC for optical communication receiver resistant for the oscillation and the noise can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current-voltage conversion circuit, and in particular to a current-voltage conversion circuit that is used in an optical communication IC and has a circuit configuration that is difficult to oscillate.

[Conventional technology]

FIG. 2 shows an example of a conventional current-voltage conversion circuit used in a receiver of an optical communication IC. In the figure, a first transistor (hereinafter referred to as Tr) 1 is a photodiode 1.
The collector of the first Tr1 is connected to the first resistor 5, and the signal is transmitted to the base of the second Tr2. second T
The emitter of r2 is connected to the anode of diode 9,
From the cathode of the diode 9 through the second resistor 6, the first
Negative feedback is provided to the base of Trl.

An output 8 of this current-voltage conversion circuit is input to an AGC amplifier circuit 7.

Next, the operation will be explained.

The optical signal is converted into a current by the photodiode 1o and becomes a base current of the first Trl, which is amplified by the first Trl and converted into a voltage by the first resistor 5. This voltage is amplified by the second Tr2 and the third Tr3, and the output thereof is input to the AGC amplification circuit 7 at the next stage.

The AGC amplifier circuit 7 has a single-ended input,
This person's current voltage conversion circuit including GC amplifier circuit 7 is number 1
It has a band of 00MHz. The AGC amplifier circuit 7 is designed so that even if the optical input level changes, that is, even if the output level of the current-voltage conversion circuit changes, the output level of the AGC amplifier circuit 7 remains constant, and is usually several tens of dB. It has gain.

[Invention or problem to be solved]

Since the conventional device is configured as described above, the AGC
Optical communication receiver ICs that combine an amplifier circuit and a current-voltage converter circuit on a single chip have problems such as high gain (and wide band), which makes them prone to oscillation and poor noise characteristics.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a current-voltage conversion circuit that is resistant to oscillation and noise and incorporates an AGC amplifier circuit.

[Means to solve the problem]

The current-voltage conversion circuit according to the present invention has a configuration in which the input of the AGC amplifier circuit is not a single-ended input, but a bias circuit having the same circuit configuration as the current-voltage conversion circuit itself, and a double-ended input. It is something.

[Effect]

In this invention, the bias circuit which uses double-end input as the input of the AGC circuit has the same circuit configuration as the main body of the current-voltage conversion circuit, but is a circuit to which no optical input is applied. Therefore, this bias circuit is a circuit that outputs the same output as the main body of the current-voltage conversion circuit when there is no signal. Therefore, even if it returns to the output of the AGC amplifier circuit or the input of the current-voltage conversion circuit via the power supply, ground, etc., it will act as a common mode (in-phase signal) signal due to the bias circuit, which is composed of the same circuit. No input enters the AGC amplifier circuit, and since this circuit as a whole transmits signals in a differential format, it is resistant to oscillation and noise.

〔Example〕

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

FIG. 1 shows the circuit configuration of a current-voltage conversion circuit according to an embodiment of the present invention. Also, Figure 3(a) shows the output waveform of the current-voltage conversion circuit that converts current into voltage, Figure 3(b) shows the output waveform of the bias circuit, and Figure 3(C) includes the AGC amplifier circuit. The output waveforms of the current-voltage conversion circuit are shown in each figure.

In FIG. 1, the first Trll is the photodiode 2
0 is connected to the input terminal of the current-voltage conversion circuit main body 30, and is a Tr that inputs the optical signal input to the photodiode 20 converted into a current. Further, the emitter of the first Trll is grounded, and its collector is connected to the base of the second Trl2 and also to the first resistor 15. The optical signal input to the photodiode 20 is then converted into a current, and the signal is transmitted to the base of the second Trl2 via the collector of the first Tril. The emitter of the second Trl2 is connected to the anode of the diode 19, and the cathode of the diode 19 is negatively fed back to the base of the first Trl2 through the second resistor 16. Further, the collector of the second Trl2 is connected to the base of the third Trl3, and the signal amplified by the third Trl3 is inputted to the AGC amplifier circuit 17 from the collector.

A bias circuit 40 having the same configuration as the current-voltage conversion circuit main body 30 is also connected to another input of the same <AGC amplifier circuit 17. This bias circuit 40 has the same circuit configuration and the same chip wiring arrangement as the current-voltage conversion circuit main body 30, but its input does not have an input terminal to which the photodiode 20 is connected.

Next, the operation will be explained.

First, the signal converted into a current by the photodiode 20 becomes the base current of the first Trll,
r l 1 amplifies this, and the first resistor 15 converts it into a voltage. This voltage is amplified by the second Trl2 and the third Trl3, and this output is used for the next stage A, G.
The signal is input to the C amplifier circuit I7. The output of this current-voltage conversion circuit main body 30 is shown in FIG. 3 (a+).

Next, explaining the bias circuit, the current-voltage conversion circuit main body 30 and the bias circuit 40 have the same circuit configuration,
In addition, the layout and wiring circuits are made up of the same circuit elements, and the circuits are only connected to optical input or not. That is, this bias circuit 40 outputs the same output as the current-voltage conversion circuit main body 30 when there is no signal.

The output waveform of this bias circuit 40 is shown in FIG. 3(b). Therefore, even if it returns to the output 18 of the AGC amplifier circuit 17 or the input of the current-voltage conversion circuit 50 via the power supply, ground, etc., it will act as a common mode (in-phase signal) signal by the bias circuit 40, which is composed of the same circuit. Then A, G C
No input is input to the amplifier circuit 17. In other words, since this optical communication receiver circuit transmits signals in a differential format, only pure signal components are amplified as shown in FIG. 3(C), making it resistant to oscillation and noise.

As described above, in this embodiment, the current-voltage conversion circuit main body 30 and the bias circuit 40 have the same circuit configuration or wiring circuit with the same circuit elements, and the inputs of the A and G C amplifier circuits 17 are double-ended. Since the input is in differential format, the AGC
The amplifier circuit 17 can also be configured in a differential format,
Therefore, it is possible to transmit signals in a differential format from input to output. Therefore, it is possible to create a circuit configuration that is resistant to oscillations caused by unnecessary common mode (in-phase signals) signals. Therefore, it is possible to obtain an optical communication receiver IC that is resistant to oscillation and noise.

Incidentally, in the above embodiment, the input terminal of the bias circuit 400 is not connected to anything, but it is of course possible to connect it to a dummy diode.

〔Effect of the invention〕

As described above, according to the current-voltage conversion circuit according to the present invention, the current-voltage conversion circuit main body and the bias circuit have the same circuit configuration and the same arrangement and wiring circuit of the circuit elements, and the input of the AGC amplifier circuit is double-ended. Since the input is in differential format, it becomes possible to transmit the signal in differential format from the input to the output.
It is possible to create a circuit configuration that is strong against unnecessary signals (in-phase signals). Therefore, it is possible to obtain a current-voltage conversion circuit that is resistant to oscillation and noise.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram showing the configuration of a current-voltage conversion circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a current-voltage conversion circuit according to a conventional example, and FIG. ) is a waveform diagram showing the output waveform of the current-voltage conversion circuit main body according to one embodiment of the present invention, FIG. 3(b) is a waveform diagram showing the output waveform of the bias circuit according to one embodiment of the present invention, C) is a waveform diagram showing an output waveform of a current-voltage conversion circuit including an AGC amplifier circuit according to an embodiment of the present invention. In the figure, 1 and 11 are the first Tr, 2.12 is the second Tr, 3.13 is the third Tr, 5.15 is the first resistor,
6 and 16 are second resistors, 7 and 17 are AGC amplifier circuits, and 8
, 18 are outputs, 9 and 19 are diodes, 10.20 are photodiodes, 30 is a current-voltage conversion circuit main body, 40 is a bias circuit, and 50 is a current-voltage conversion circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) Connect the collector of the first Tr that amplifies the current to the second Tr.
the emitter of the second Tr and the anode of the diode are connected, the cathode of the diode and the base of the first Tr are connected to apply negative feedback, and the first Tr is used as a signal current input terminal. A single-ended input current-voltage conversion circuit using the base of a Tr; a second bias circuit having the same configuration as the current-voltage conversion circuit but without a signal current input terminal; and an output of the current-voltage conversion circuit. and an AGC amplifier circuit whose inputs are the output of the bias circuit and the output of the bias circuit, the entire circuit being integrated into one chip.