JPH02278906A - Optical reception circuit - Google Patents

Abstract

PURPOSE:To expand the dynamic range of an optical reception circuit with respect to an optical incident intensity by varying a trans-impedance of a preamplifier of the trans-impedance type when the incident strength of an optical signal is stronger. CONSTITUTION:When an optical signal is made incident in a photodetector 1, the signal is converted into an electric signal in the photodetector 1 and amplified by a preamplifier 4 of the trans-impedance type. When the light incidence strength is increased, the output of the preamplifier 4 is increased and exceeds the control range of an AGC circuit 2, the AGC control voltage from an AGC control amplifier 3 is utilized to control a gate-source voltage of an N-channel MOS transistor(TR) Q2 of the preamplifier 4 to vary the ON- resistance of the TR Q2 thereby varying the open loop gain of the preamplifier 4 and varying the trans-impedance of the preamplifier 4. Thus, the saturation of the preamplifier is prevented and the dynamic range of the optical reception circuit is expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical receiving circuit, and more particularly to an optical receiving circuit including a light receiving element and a transimpedance type preamplifier circuit.

[Conventional technology]

Conventionally, this type of optical receiving circuit includes a light receiving element 1 and a transimpedance type preamplifier 4, as shown in an example in FIG. , an AGC" circuit 2, and an AGC control amplifier 3.

In FIG. 3, the cathode of the light receiving element 1 is connected to the power supply terminal of the power supply VCC, and the anode is connected to the transistor Q! The emitter of the transistor Qt is connected to the ground terminal, and the collector is connected to the power supply VCC through the resistor R1.
connected to. The base of transistor Q5 is transistor Q! The collector is connected to the power supply VCC, and the emitter is connected to the input of the level shift circuit D1.

The output of the level shift circuit D1 is connected to the base of the transistor Ql via a feedback resistor Ftt, and further connected to the base of the transistor Ql through a resistor R2.
connected to the ground terminal via.

Now, when an optical signal is input to the light receiving element 1, the optical signal is converted into an electrical signal by the light receiving element 1, and the optical signal is converted into an electrical signal by the transimpedance type preamplifier 4. The signal amplified by AG
The signal is input to the C circuit 2 and controlled by the AGC circuit 2 and AGC control amplifier 3 so that the signal output has a constant amplitude.

[Problem to be solved by the invention]

In the conventional optical receiving circuit described above, as the intensity of light incident on the light receiving element 1 increases, the current in the light receiving element increases and the transimpedance of the preamplifier is fixed.
The output amplitude of the preamplifier increases in proportion to the received power, and A
The signal increases to the upper limit of the input dynamic range of the GC circuit. Furthermore, as the incident light intensity increases, the transistor Q1 of the preamplifier becomes saturated, and therefore the waveform of the output signal of the preamplifier is distorted, furthermore, it becomes unreceivable beyond the operating range, and the so-called dynamic The drawback is that the range cannot be expanded.

[Means to solve the problem]

The optical receiving circuit of the present invention includes a light receiving element that receives an optical signal and converts it into an electrical signal, a first resistor, a first transistor, and a second CMOS that are inserted in series between a power supply terminal and a ground terminal.
a first stage amplifier circuit comprising a transistor, the base of the first transistor being connected to the anode of the light receiving element; and a first stage amplifier circuit inserted in series between the power supply terminal and the ground terminal, the base of which is connected to the collector of the first transistor. a third transistor connected to the base of the first transistor, a level shift circuit and a second resistor, and a connection node between the level shift circuit and the second resistor connected to the base of the first transistor via a feedback resistor; a preamplifier including a second stage amplifier circuit; and an AGC whose input end is connected to a connection node between the level shift circuit and the second resistor and whose output end is connected to an output terminal.
an input terminal connected to an output terminal of the AGC circuit, and an output terminal connected to a control voltage input terminal of the AGC circuit and the second M circuit;
(OS) AGC control amplifier connected to the gate of the run lister.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

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

As shown in FIG. 1, the cathode of the light receiving element 1 is connected to the power supply VC.
It is connected to the power supply terminal of O and receives optical signals and converts them into electrical signals.

The transimpedance type preamplifier 4 is connected to the power supply ■c
A first resistor R1 and a first resistor R1 are connected between the power supply terminal and the ground terminal of
transistor Q1 and second N-type MO3) run lister Q
2 are connected in series in that order, and the base of the transistor Q1 is connected to the anode of the light receiving element 1. A third transistor Qs and a level shift circuit are connected between the power supply terminal of the power supply VCC and the ground terminal. Circuit D+ and second resistor R2
and a second stage amplifier circuit in which the transistors are connected in series in that order and the base of the third transistor Q3 is connected to the collector of the first transistor Ql, a level shift circuit, and a resistor R.
The connection node N1 with 2 is connected to the base of the transistor (L) via the feedback resistor Re.

The AGC circuit 2 has an input end connected to the connection node N1, and an output end connected to the output terminal OUT. Further, an AGC control amplifier 3 that generates an AGC control voltage for automatic gain control of the AGC circuit 2 has an input terminal connected to the output terminal of the AGC circuit 2, and an output terminal connected to the control voltage input terminal of the AGC circuit 2 and the MOS transistor 2. connected to the gate.

In this configuration, when an optical signal is incident on the light receiving element 1, the optical signal is converted into an electrical signal, and is amplified by the preamplifier 4, and the output amplitude of the AGC circuit 2 is kept constant by the AGC circuit 2 and the AGC control amplifier 3. controlled so that it is maintained.

FIG. 2 is an equivalent circuit diagram of a transimpedance type amplifier circuit for explaining the principle of the preamplifier shown in FIG. 1.

In FIG. 2, the transimpedance ZT is expressed by equation (1), where Zp is the feedback impedance, Z is the input impedance, and A is the open loop gain.

2 pieces = Z p / (1+ (1+ Z F /
Z + > / A )...(1) Also, the open loop gain A of the preamplifier is determined by the resistance R1, which is the collector resistance of the transistor Q1 in FIG. Determined by the resistance ROM, the on-resistance Row! , tN type MO
S) The gate-source voltage of the runlister Q2 is V, H, the threshold voltage is 7, the gain coefficient is β, Vas
When -Vy>VD, it is expressed as equation (2).

RoN=(β<VasVT))−'
(2) Therefore, when the incident light intensity increases and the output of the preamplifier 4 increases and exceeds the control range of the AGC circuit 2, the AGC control voltage from the AGC control amplifier 3 is used to convert the N-type The transimpedance of the transimpedance type preamplifier 4 is controlled by controlling the gate-source voltage G5 of the MOS transristor Q2, varying the on-resistance ROM of the N-type MOS transristor Q2, and changing the open loop gain of the preamplifier. Make it variable. In this case, N
In order to appropriately design the on-resistance ROM of the type MOS) run lister Q2, it is necessary to consider the gate aspect ratio of the MOS transistor.

From the above results, when the incident intensity of the optical signal becomes strong, by varying the transimpedance of the transimpedance type preamplifier, the saturation state of the preamplifier can be suppressed, and the dynamic range of the optical receiver circuit with respect to the incident optical intensity can be increased. can be expanded.

FIG. 4 is a circuit diagram of a second embodiment of the present invention.

As shown in FIG. 4, in the second embodiment, instead of the second N-type MOS run resistor Q2 of the transimpedance type preamplifier 4 of the first embodiment shown in FIG. The source is connected to the power supply terminal of the
The gate is connected to the resistor R of the AGC control amplifier 3.
This embodiment is the same as the first embodiment described above except that a preamplifier 4b is provided with a second P-type MOS transistor Q4 connected to the GC control voltage output terminal.

In such a configuration, when the incident intensity of the optical signal becomes strong,
By the AGC control voltage of the AGC control amplifier 3, the P-type Mo
By changing the voltage between the gate and source of the S transristor Q4 and varying the on-resistance of the MOS transristor, a transimpedance type preamplifier 4. By changing the open loop gain of the transimpedance, the transimpedance is changed as a result.

〔Effect of the invention〕

As explained above, the present invention achieves a saturation state of the transimpedance type preamplifier by varying the transimpedance of the transimpedance type preamplifier that amplifies the output of the light receiving element when the incident intensity of the optical signal is strong. This has the effect of expanding the dynamic range of the optical receiving circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention, and FIG. 2 is a circuit diagram of a first embodiment of the present invention.
An equivalent circuit diagram of a transimpedance type amplifier circuit for explaining the principle of the preamplifier shown in the figure, FIG. 3 is a circuit diagram of an example of a conventional optical receiver circuit, and FIG. It is a circuit diagram. 1... Light receiving element, 2... AGC circuit, 3... AG
C control amplifier, 4.4-. 4b...Preamplifier, Dl
...Level shift circuit, Ql, Q3...Transistor, Q2...N-type MOS transistor, Q4...P
type MOS transistor, R,, R2...resistor, R1...
...Return resistance. t1 person Rokusenshi Uchihara Shinmantu shoulder figure Mantu Mantu

Claims (1)

[Claims] It consists of a light receiving element that receives an optical signal and converts it into an electrical signal, a first resistor inserted in series between a power supply terminal and a ground terminal, a first transistor, and a second CMOS transistor. a first stage amplifier circuit whose base is connected to the anode of the light receiving element; a third transistor which is inserted in series between the power supply terminal and the ground terminal and whose base is connected to the collector of the first transistor; Before comprising a second stage amplifier circuit, which includes a shift circuit and a second resistor, and connects a connection node between the level shift circuit and the second resistor to the base of the first transistor via a feedback resistor. an AGC circuit whose input end is connected to the connection node between the level shift circuit and the second resistor and whose output end is connected to the output terminal;
An optical receiving circuit comprising: an AGC control amplifier connected to an output end of a GC circuit, the output end of which is connected to a control voltage input end of the AGC circuit and a gate of the second MOS transistor.