JP2903856B2 - Preamplifier for optical reception - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preamplifier for receiving light in optical communication.

[0002]

2. Description of the Related Art Conventionally, there is an optical receiving preamplifier of this kind shown in FIG. FIG. 2 is a circuit diagram of a conventional example. In this figure, two FETs 1 and 4 and a capacitor 3
This amplifier is composed of the resistors 13, 5, 6, 8 and the bias power supply 7. The first-stage FET 1 is a source-grounded type, and the second-stage FET 4 is a source-floor-type amplifier. By applying a bias voltage to the gate of the second-stage FET 4, the operating point of the second-stage FET 4 is determined. By connecting the feedback resistor 202 between the source of the second-stage FET 4 and the gate of the first-stage FET 1, the operating point of the first-stage FET 1 is also determined. That is, the amplifier is of a transimpedance type in which resistance feedback is applied between the input and output terminals of the amplifying unit. Therefore, the amplifier operates as a current-voltage switch.

[0003]

In order to realize high sensitivity as a characteristic of the optical receiving amplifier, it is desirable that the feedback resistance is large in terms of S / N and gain. Then, since most of the photocurrent flowing through the light receiving element flows through the feedback resistor, a large change in the photocurrent appears as a change in the voltage across the feedback resistor. This means that when the photocurrent increases, the gate bias of the first-stage FET changes greatly, and the drain current increases due to a large change in the operating point, the drain-source voltage decreases, and the output signal is distorted. There is a problem that a normal output cannot be obtained.

[0004]

A preamplifier for optical reception according to the present invention comprises a first source grounded source having a gate connected to an input terminal .
And the gate is connected to the drain side of the first FET.
A second FE on the source floor connecting the source to the output terminal
Up of a T, a resistor circuit for a feedback connecting the other end one end to a source of the second FET to the gate of the prior SL first FET
In a transimpedance type optical receiving preamplifier to be formed, a resistance circuit including a first resistor and a second resistor connected in series with the first resistor, and a non-inverting input connected to a drain of the first FET. The inverting input to the specified reference voltage source
An operational amplifier is provided for connecting an output to a connection point between the first resistor and the second resistor.

[0005]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of the present embodiment. Are added op amp 9 in the circuit of FIG. 2, the drain of the non-inverting input of the first stage FET1 of the added operating <br/> amplifier 9,
The drain current of the first-stage FET 1 can be controlled by connecting the inverting input to the reference voltage source 10 and connecting the output via the resistor 11 and the resistor 12 obtained by dividing the feedback resistance value.

That is, when the input signal from the input terminal V1 is small, the circuit operates in the same manner as the conventional amplifier. However, since the voltage between both ends of the resistor 12 is reduced by the operation of the operational amplifier 9 , the gate bias of the first-stage FET 1 is reduced accordingly, and as a result, the increase in the drain current of the first-stage FET 1 is suppressed. The output signal of the output terminal V0 can be kept normal.

[0007]

As described above, according to the present invention, when the input signal becomes large, the source bias of the second-stage FET is controlled to prevent the operating point of the first-stage FET from shifting. This has the effect of preventing the above-described occurrence of waveform distortion of the output signal.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

1,4 FET 3 Condensed 2,5,6,8,11,12 Resistor 7,10 Reference voltage source 9 Operational amplifier

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03G 3/12 H03F 1/34 H03F 3/08 H03G 11/04

Claims (1)

(57) [Claims] 1. A source-grounded first FET having a gate connected to an input terminal, and a gate connected to a drain of the first FET.
Connect the source to the output terminal on the second side of the source floor
And one end is connected to the source of the second FET and the other end is
Resistor for feedback to be connected to the gate of the prior SL first FET
In transimpedance optical receiver preamplifier constituting between, said resistor circuit comprising a first resistor and this series-connected <br/> second resistor, a non-inverting input < an operational amplifier for connecting an inverting input to a drain of the first FET to a predetermined reference voltage source and an output to a connection point between the first resistor and the second resistor, respectively. Characteristic preamplifier for optical reception.