JPS63181536A - Optical receiving equipment - Google Patents

Abstract

PURPOSE:To obtain an optical receiving equipment having good sensitivity and wide dynamic range by constituting a negative feedback loop by means of a constant-current circuit in order that the signal current of a photoelectric converting element is not increased by the input of excessive light beam. CONSTITUTION:When the input of the excessive light beam is supplied to an avalanche photodiode 1, the output amplitude from a preamplifier circuit 3 is increased to excess to saturate. Since the output from a second peak value detection circuit 11 which detects the output amplitude becomes larger, difference between a second reference voltage 12 and the output from the circuit 11 becomes larger and the output voltage value of a second error amplification circuit 13 becomes higher. Since the current capacity i1 of the constant-current circuit 14 connected to the second error amplification circuit 13 becomes larger if the output voltage value becomes higher, the current i2 flowing in the first and second load resistances 15 and 16 of the avalanche photodiode 1 is lowered and the saturation of the output from the pre-amplifier circuit 3 can be improved, thus the negative feedback loop can be obtained. When the input of light beam is small, the current capacity of the constant-current circuit 14 is equal to zero and the output from the pre-amplifier circuit 3 is controlled so that it becomes the maximum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical receiver that is a component of an optical communication system.

[Conventional technology]

Figure 4 is a block diagram showing a conventional optical receiver shown in Figure 2 of the Japan Industrial Technology Center [Optical Communication System JP 221] published in March 1980. A through avalanche photodiode that converts a signal into an electrical signal, (2) a high voltage generation circuit that supplies bias for this avalanche photodiode (1),
(31 is a preamplifier circuit that converts the signal due to the current change of the avalanche 7 otodiode fi+ into a signal due to a change in the lamination pressure, (41 is a variable gain whose amplification gain changes in response to the output of this preamplifier circuit (3) The amplifier circuit (5) is a main amplifier circuit that receives the output of the variable gain amplifier circuit (4) and amplifies it with a constant gain.

fil ldA peak value detection circuit that detects the output amplitude level of this main amplifier circuit (5), (7) is the basic thread voltage, (8-
is an error amplification circuit that amplifies the error between this baseline voltage and the output of the peak value detection circuit (6), and controls the gain control voltage of the variable gain amplifier (4) and the output voltage of the high voltage generation circuit (2). , (9) is an identification reproducing circuit for reproducing the waveform of the output signal of the main amplifier circuit (5), and α1 is a signal output terminal of this identification reproducing circuit (91).

Next, th work will be explained. Optical input signal Pin (W
) H is converted into an electrical signal ia (A) by the avalanche photodiode (1). This relationship can be expressed as an equation as shown below.

1a=a −M −Ptn (
11 Output chamber i1 of avalanche photodiode (1)
a is a preamplifier circuit (3) having a feedback resistance Rf (Ω)
The current-to-voltage is converted by , and the output of vp (V) is generated.

Vp: Rf ・1af21 The output of the preamplifier circuit (3) is connected to the variable gain amplifier circuit (41
゜It is amplified by the main amplifier circuit (5), and the identification reproducing circuit (
In step 9), it is determined whether the digital binary values are "1" or "0".

Since it is desirable that the signal amplitude supplied to the input of the identification and regeneration circuit (9) always be a constant value, a variable gain amplifier circuit (4I whose gain is changed according to changes in the optical input level) is used. ), this multiplication factor M can be increased by changing the bias pressure supplied to the avalanche photodiode (1).
[AGCj (abbreviation for auto cane control) feedback loop is used to vary the value. The output amplitude value of the main amplifier circuit (5) can be adjusted by the reference voltage (Vref) of the error amplifier circuit (8), which is a component of the AG6 feedback loop.

[Problem that the invention seeks to solve]

Conventional optical receivers are configured as 1 or more, so if the feedback resistance value of the preamplifier circuit is increased in order to improve the minimum received light power, when the optical input level is high, the preamplifier circuit and There is a problem in that the variable gain amplifier circuit tends to become saturated.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain an optical receiving device with high sensitivity and a wide dynamic range.

[Means for solving problems]

In the optical receiving device according to the present invention, a second error amplifier is connected to the output of the preamplifier circuit via a second peak value detection circuit, and the output of the second error amplifier circuit is connected to the constant current circuit. It is connected to the anode side of the avalanche photodiode through the avalanche photodiode.

[Effect]

This optical receiving device in EJA (/l) uses a constant current circuit connected to the anode 911+ of the avalanche photodiode, so that the signal current is reduced when an excessive optical input is supplied to the avalanche photodiode.

The saturation level of the preamplifier is improved.

〔Example〕

FIG. 1 is a block diagram of an optical receiver showing an embodiment of the present invention. In FIG. 1, (1) is an avalanche photodiode, and (2) is a high voltage generation circuit.

(3) 41-digit preamplifier circuit, (41-digit variable gain amplifier circuit, (
5) is the main amplifier circuit; 161 is the first peak value detection circuit;
(71st reference voltage, (81st error amplification circuit), (9) is an identification reproducing circuit, Ql is an output terminal υ, and the above (11th to axis are the conventional ones shown in Figure 4) It's the same.

αυ is the second
02 is the second base thread voltage, 03 is the peak value detection circuit a for this second base thread voltage az and the ν2.
The second error amplification circuit α4 that amplifies the difference between the outputs of 0 and 0 is a constant current circuit whose current capacity varies depending on the output voltage of the second error amplification circuit α3.

In addition, Fig. 2 is a diagram explaining the operation of the constant current circuit α in detail, but in Fig. 2, a! 19 is a first load resistance of the avalanche photodiode, αG is a second load resistance, and αη is an NPN constant current source transistor l.

a8 is the emitter resistance of this constant current source transistor αη.

The first base bleeder resistor (A) determines the base bias of the a*urMe fixed current source transistor, and (A) is the second base bleeder resistor.

± As explained previously, the optical input signal Pin is transmitted through the avalanche photodiode (11) and the preamplifier circuit (11).
31 into a voltage signal Vp.

(11, (2+ formula) If this voltage signal is expressed by the formula, it becomes VC as follows.

Vp ==Rf, la ” Rf-a-M-Pin
According to the f31± formula, when an excessive optical signal (Pin) is supplied, the device amplifier circuit (3)
Although it is clear that the output amplitude vp increases, a saturation state occurs due to the limitation due to one circuit configuration (see Fig. 3).
IM). When the output amplitude (vp) of the preamplifier (31) is saturated, the output waveform of the main amplifier circuit (5) is distorted, and faithful reproduction cannot be performed by the discrimination/reproduction circuit (9).Therefore, in order to improve the saturation level, , it is expected (from formula 31) that when the optical input becomes large, it is sufficient to reduce the signal current of the avalanche photodiode (11).

In this invention, in order to reduce the signal current of the avalanche photodiode (11), a constant current circuit θ having a function of flowing a constant current is provided, and the excess 1' current is branched to this. As an example, as shown in Fig. 2, an NPH constant current source transistor 40'j is used. By controlling the base bias of this transistor, the terminal voltage of the emitter resistor α8 changes, and the current capacity can be varied by 11. By changing this current capacity 11, the signal current 12 of the avalanche photodiode (11) flowing through the first and second load resistors a9 and αe can also be changed accordingly. The current io flowing from (2) into the avalanche photodiode fil, the current capacity 11 of the constant current circuit 041, and the first and second load resistances σS of the avalanche 7 photodiode (1).

This is because the following relational expression holds true between the current 12 flowing through the current 69 and the current 12 flowing through the current 69.

10==11+12 +4! Next, the principle of control operation of the constant current circuit will be explained.

Excessive optical input causes avalanche photodiode (Ilr
When supplied, according to the relationship of equation (3), the device amplifier circuit (31
The output amplitude of increases excessively and saturates. Since the output of the second peak value detection circuit (Ill) which detects this output amplitude also increases, the difference between this and the second reference voltage α increases, and the output of the second error amplification circuit a3 increases. The voltage value increases.If this output voltage value becomes high, the current capacity Mc11 of the constant current circuit I connected to the error amplifying circuit α3 of the brush 2 becomes large.For the above reason, the avalanche photodiode is 1st. Current 1 flowing through 20th load resistance a destination tJI3
2 decreases, forming a negative feedback loop in which the saturation of the output of the preamplifier circuit (31) is improved.
When the optical input is small, the current capacity of the constant current circuit 0 is equal to 0, and the output of the preamplifier circuit (3) is controlled to be the largest.

At the saturation level of the conventional preamplifier circuit (3).

If the circuit device of the present invention were to be used to control so that 11 and 12 were equal, the improvement would be approximately twice that of the conventional one, as shown in the diagram in FIG.

Note that in the above embodiment, an avalanche photodiode (1) is used as the photo-electrical conversion element, but a photodiode that does not have a multiplication function may also be used.

〔Effect of the invention〕

As described above, according to the present invention, the negative feedback loop f is configured using a constant current circuit so that the signal '(flow) of the optical-to-electrical conversion element does not become thicker due to excessive optical input. This has the effect of allowing a large value to be set and providing an optical receiver with high sensitivity and a wide dynamic range.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an optical receiving device according to an embodiment of the present invention, Fig. 2 is a connection diagram of an example of the configuration of a constant current circuit, and Fig. 3 is a diagram showing the optical input level and the output voltage amplitude of the preamplifier. FIG. 4 is a block diagram showing a conventional optical receiver. (11 is an avalanche photodiode, (2) is a high voltage generation circuit, C3) is a preamplifier circuit, (42-digit variable gain amplifier circuit, (5) is a main amplifier circuit, (6) is a first peak value detection circuit , (7) is the first reference voltage, (81 is the first error amplification circuit, (91 is the identification reproducing circuit, all is the second peak value detection circuit, α2 is the second reference voltage, 63jd is the first reference voltage, 2, the error amplification circuit (I4 is a constant current circuit). Note that in Figure 1, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] an optical-electrical conversion element that converts an input optical signal into an electrical signal;
A preamplifier circuit that converts a signal caused by a current change of this opto-electric conversion element into a signal caused by a voltage change, a variable gain amplifier circuit whose amplification gain changes in response to the output of this preamplifier circuit, and this variable gain amplification circuit. a main amplifier circuit that receives the output of the circuit and amplifies it with a constant gain; a first peak value detection circuit that detects the output amplitude level of the main amplifier circuit; a first reference voltage; and the first peak value detection circuit. Amplify the difference in the output of the circuit,
a first error amplification circuit that supplies a gain control voltage of the variable gain amplifier and a voltage that controls the bias of the opto-electric conversion element; a high voltage generation circuit for controlling the bias of the element; an identification and regeneration circuit for reproducing the waveform of the output signal of the main amplifier circuit; a second peak value detection circuit for detecting the output amplitude level of the preamplifier circuit; a second error amplification circuit for amplifying the difference between the second reference voltage and the output of the second peak value detection circuit; An optical receiver comprising: a constant current circuit that supplies an anode of a conversion element.