JPS62114341A - Light reception level monitor circuit - Google Patents

Abstract

PURPOSE:To prevent the change of a monitor voltage even if the mark rate of an input optical signal is changed, by synthesizing a bias voltage value and a value, which is obtained by dividing a DC current flowing to an APD by the mark rate of the input optical signal, to obtain a monitor level. CONSTITUTION:The output of a data discriminating circuit 10 is processed by an LPF 13 to become a DC voltage VM proportional to the mark rate (m) of the optical pulse signal and is supplied to a divider 14. A voltage VDC proportional to the DC current supplied to an APD 1 from a differential amplifier 11 is supplied to the divider 14 also. A divided value V2=VDC/VM from the divider 14 and the bias voltage V1 of the APD 1 are synthesized by an adder 12 to become a monitor voltage V3. This voltage V3 is not changed even through the mark rate (m) is changed, and the voltage V3 is increased for the rise of the input optical level and is not affected by the mark rate.

Description

[Detailed Description of the Invention] [Summary] Synthesized from a value obtained by dividing a voltage proportional to the DC current flowing through an avalanche photodiode (hereinafter referred to as APD) by a voltage proportional to the mark rate of the input signal and the bias voltage of the APD. The value obtained is the monitor voltage.

[Industrial application field]

The present invention relates to an optical communication device, and more particularly to an optical reception level monitor circuit.

A receiving device for optical communication uses a circuit that constantly monitors the level of an optical signal sent from the transmitting side. A circuit like this is called an optical reception level monitor circuit,
Conventional optical reception level monitor circuits have a drawback in that when the mark rate of an input optical signal changes, different monitor voltages are obtained for the same peak value, and an improvement has been desired.

[Conventional technology]

Conventionally, there are various methods for optical reception level monitoring circuits. For example, a wide monitoring range is achieved by combining both the bias voltage of an APD and the AGC voltage of an electric amplifier.

FIG. 3 is a diagram showing an example of a conventional optical receiving circuit and an optical receiving level monitor circuit.

FIG. 4 is an explanatory diagram of the operating characteristics of a conventional optical reception level monitor circuit.

In the figure, 1 is an APD, 2 is a resistor, 3 is a capacitor, 4 is a preamplifier, 5 is an AGC amplifier, 6 is an AGC control circuit, and 7 is a
is a DC-DC converter, 8 is an equalizer (EQL), 9 is a timing extraction circuit, and 10 is a data identification circuit (DEC)
, 11 is a differential amplifier, and 12 is an adder. The same symbols represent the same objects throughout the following discussion.

The optical signal enters the APDI, is converted into an electrical signal, the DC component is removed by the capacitor 3, and only the pulse component is amplified by the preamplifier 4.

Next, it is amplified by AGC amplifier 5, and this output is AGC
It enters the control circuit 6, EQL 8, and timing extraction circuit 9.

The output of the AGC control circuit 6 controls the gain of the AGC amplifier 5 so that the output level of the AGC amplifier 5 is constant. At the same time, another output of the AGC control circuit 6 is a DC-DC converter 7.
The output of the DC-DC converter 7 supplies direct current to the APD 1 via the resistor 2. This circuit changes the output DC voltage when the input optical signal is low level and converts it into an APD.
The multiplication factor of I is increased to control the output level of the AGC amplifier 5 to be constant.

Further, the output of the AGC amplifier 5 is waveform-equalized by an EQL8, and a timing pulse is extracted by a timing extraction circuit 9.

These waveform-equalized signals and timing pulses are sent to a data identification circuit (DEC) 10, where the data is identified.

A monitor circuit consisting of a differential amplifier 11 and an adder 12 is usually used to monitor the operation of the optical receiver circuit.

In this monitor circuit, the AP
A voltage proportional to the direct current flowing through Dl. .

Then, the adder 12 calculates the voltage VDC and APD 1
A method was adopted in which the bias voltages (1) were synthesized and this synthesized voltage was monitored.

This method has advantages such as a wide dynamic range and no adverse effects on the AGC loop, and is a widely used circuit.

[Problem that the invention seeks to solve]

However, if the mark rate of the first entry Kai No. 8 changes, there will be the following drawbacks.

When the mark rate of the optical input signal changes, the output level of the differential amplifier 11, that is, the voltage VOC changes.

That is, when the mark rate of the optical input signal changes, the value of the current flowing through the resistor 2 to the eight PDs 1 changes.

At the light level X as shown in FIG. 4, as the mark rate m of the optical input signal increases, the voltage VDC also increases, and the mark rate m
When the voltage VIllc decreases, the voltage VIllc also decreases.

For this reason, the composite voltage (monitor voltage) also increases or decreases, but the output level of the AGC amplifier 5 does not change due to the automatic gain control operation of the AGC amplifier 5.

When the mark rate changes in this way, the conventional monitor system displays that the optical input signal has changed, but there is a drawback in that the output level of the AGC amplifier 5 does not actually change.

An object of the present invention is to provide an optical reception level monitor circuit in which a monitor voltage does not change even if the mark rate of an input optical signal changes.

[Means for solving problems]

Avalanche is the way to solve problems! .

In an optical receiving circuit that stabilizes the output amplitude of the data identification circuit by controlling the multiplication factor of the photodiode and the amplification degree of the electric AGC amplifier, the bias voltage of the avalanche photodiode and the direct current flowing through the avalanche photodiode are controlled. This problem can be solved by combining the current and the value obtained by dividing the mark rate of the input optical signal to obtain a monitor level.

[Function] When the mark rate changes, the optical reception level monitor circuit according to the present invention corrects the direct current flowing through the avalanche photodiode and synthesizes it to obtain a monitor voltage, so that the mark rate changes. The effect is that the monitor voltage does not change even if the voltage changes.

〔Example〕

FIG. 1 is a diagram showing an embodiment of an optical reception level monitor circuit according to the present invention.

FIG. 2 is a diagram showing the operating characteristics of the optical reception level monitor circuit according to the present invention.

In the figure, 13 is a low-pass filter, and 14 is a divider.

The present invention will be described in detail below with reference to the drawings.

In the present invention, the low-pass filter 13 is
The low-pass filter 13 extracts the DC component contained in the received signal (pulse signal). This DC component voltage value V, 4 is a value proportional to the mark rate m of the pulse signal.

Therefore, the output voltage v of the differential amplifier 11 explained in the conventional method
llc and the voltage VM proportional to the mark rate m are input to the divider 14 to obtain vnc÷o.

Now ■. , ÷V, =V, the value v2 becomes a voltage value obtained by correcting the current flowing through the APDI according to the mark rate m.

Therefore, as in the conventional method, if the voltage value V2 corrected by the adder 12 and the bias voltage ■1 of APD 1 are combined to obtain the monitor voltage ■3, this monitor voltage V3 will be the same even if the mark rate changes. It never changes.

Therefore, as shown in FIG. 2, when the input light level increases, the monitor voltage (3) increases and is no longer affected by the mark rate m.

In the explanation above, the low-pass filter 13 was connected to the output of the data identification circuit 10, but the EQ is connected as indicated by the dotted line in Figure 1.
Similar results can be obtained by connecting to the output of L8 or the output of AGC amplifier 5.

〔Effect of the invention〕

As described above in detail, the present invention has the great effect that the monitor voltage is not affected even if the mark rate of the input optical signal changes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of an optical reception level monitor circuit according to the present invention. FIG. 2 is a diagram showing the operating characteristics of the pre-receiving δ level monitor circuit according to the present invention. FIG. 3 is a diagram showing an example of a conventional optical receiving circuit and an optical receiving level monitor circuit. FIG. 4 is an explanatory diagram of the operating characteristics of a conventional optical reception level monitor circuit. In the figure, 1 is an APD, 2 is a resistor, 3 is a capacitor, 4 is a preamplifier, 5 is an AGC amplifier, 6 is an AGC control circuit, and 7
8 is a DC-DC converter, 8 is an equal liability (EQL), 9 is a 1° timing extraction circuit, and 10 is a data identification circuit (DEC).
, 11 is a differential amplifier, 12 is an adder, 13 is a low-pass filter, and 14 is a divider. Iku°f12 Figure Z

Claims (1)

[Claims] In an optical receiving circuit that stabilizes the output amplitude of a data identification circuit (9) by controlling the multiplication factor of an avalanche photodiode (1) and the amplification degree of an electric AGC amplifier (4) , A light source characterized in that a monitor level is obtained by combining the bias voltage of the avalanche photodiode (1) and a value obtained by dividing the direct current flowing through the avalanche photodiode (1) by the mark rate of the input optical signal. Reception level monitor circuit.