JPH01286654A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To facilitate the detection of a clock shut-off by unifying the sum of the peak value detecting output of a data signal and the detecting output of a low frequency component outside a data signal band. CONSTITUTION:For the output of an amplifier 2, the peak detection of a pulse waveform is executed by a detector 3, the low frequency component outside the band of a data signal out of signals to exist at the output of the amplifier 2 is removed by an LPF4, detected by a detector 5 and sent to an adder 16. The adder 16 adds the output of respective detectors 3 and 5, sends it to an LPF6 and the smoothed signal is sent to a comparator 8. The comparator 8 compares and amplifies the output of a reference voltage source 7 and the output of the LPF6 and controls a bias generating circuit 9. When the light signal input to an APD1 is shut-off, the noise or a micro prasma noise due to the dark current of the APD1 is inputted to the amplifier 2, the clock signal level of the noise at the output side is made smaller and the decision of the clock shut-off can be stably executed by a clock shut-off detector 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used in an optical receiver that demodulates, amplifies, and identifies and reproduces an optical signal intensity-modulated with a data signal consisting of a 1.0 pulse train. In particular, it relates to an automatic gain control circuit for this optical receiver.

〔overview〕

The present invention demodulates and modulates an optical signal intensity-modulated with a pulse signal.
In the automatic gain control circuit of an optical receiver that performs amplification, identification and regeneration, clock loss detection is easily detected by keeping the sum of the peak value detection output of the data signal and the detection output of the low frequency component outside the data signal band constant. It has been made possible to do so.

[Conventional technology]

As shown in FIG. 2, the conventional example includes an avalanche photodiode (hereinafter referred to as APD) 1, an amplifier 2,
Detector 3, low-pass filter 6, reference voltage source 7, comparator 8, bias generation circuit 9, discriminator 10, clock extractor 11, clock disconnection detector 12, and inhibition circuit 13
, a data signal output terminal 14 , and a clock signal output terminal 15 . The pulse-modulated optical signal input to APDl is converted into a current proportional to the multiplication factor determined by the output voltage of bias generation circuit 9 while passing through APDl, and is sent to amplifier 2. Amplifier 2 amplifies the output current of APDI to a level that allows detection, and sends it to detector 3. The detector 3 performs peak detection on the data signal output from the amplifier 2 and sends it to the low-pass filter 6 . A low-pass filter 6 smoothes the output of the detector 3 and sends it to a comparator 8. Comparator 8 compares and amplifies the output of reference voltage source 7 and the output of low-pass filter 6, and sends an error output to bias generation circuit 9. The bias generation circuit 9 has an output voltage of the comparator 8.
It supplies bias to APDl. A loop consisting of the APDI, amplifier 2, detector 3, low-pass filter 6, reference voltage R7, comparator 8, and bias generation circuit 9 is configured to provide negative feedback, and the level of the optical signal input to the APDI is This is a means for keeping the pulse amplitude of the output of the amplifier 2 constant despite changes in the characteristics of APDI due to changes in the external temperature or changes in external temperature, and is called an automatic gain control circuit (hereinafter referred to as an AGC circuit). amplifier 2
The output is branched and guided to the clock extraction circuit 11.

The clock extraction circuit 11 extracts the clock signal component of the data signal from the output of the amplifier 2, and sends the clock signal to the discriminator 10. The discriminator 10 discriminates the output signal of the amplifier 2 based on the clock signal supplied from the clock extractor 11. The reproduced data signal output from the discriminator 10 is outputted to the data signal output terminal 14 via the inhibit circuit 13. Similarly, the output of the clock extractor 11 is also output to the clock signal output terminal 15 via the inhibition circuit 13. The clock interruption detection circuit 12 receives a part of the branched output of the clock extractor 11, detects the interruption of the clock level, and sends a signal to the clock prohibition circuit 13 when the clock level is disconnected. The data signal and clock signal sent from the discriminator 10 and the clock extractor 11 are inhibited to prevent meaningless signals from being sent to the data signal output terminal 14 and the clock signal output terminal 15.

[Problem that the invention seeks to solve]

The AGC circuit of such a conventional optical receiver operates so that the output level of the low-pass filter 6 is equal to the voltage of the reference voltage source 7 even when the optical signal input to the APDI is cut off or becomes extremely small. Therefore, the output of the amplifier 2 obtained by amplifying the noise component due to the dark current of APDI or the microplasma noise component generated when APD1 breaks down, that is, the noise level, increases, and the noise level of the amplifier 2 increases.
A clock extractor 11 that extracts a clock component from the output of
Also, a clock component corresponding to the clock frequency component of the output noise of the amplifier 2 is generated in the output of the amplifier 2, and the clock disconnection detector 12 detects a clock disconnection, and the inhibition circuit 13 detects a meaningless data signal or a clock signal. There was a drawback that prohibition could not be performed stably.

The present invention aims to eliminate such drawbacks and provides an automatic gain control circuit that can suppress the influence of noise levels.

[Means for solving problems]

The present invention provides an optical receiver having opto-electric conversion means for converting an optical signal intensity-modulated with a data signal, which is a pulse train, into an electrical signal, and demodulation amplification means for demodulating and amplifying the electrical signal generated by the opto-electric conversion means. A data signal detection means is connected to the demodulation and amplification means to detect the data signal included in the electrical signal generated by the demodulation and amplification means, and the gain control of the own circuit is performed by comparing the level of the output of this detection means and the level of the reference voltage. In the automatic gain control circuit, the automatic gain control circuit includes a comparator that generates a signal equivalent to the signal, and a bias generation circuit that maintains the output level of the photoelectric conversion means within a predetermined range based on the output of the comparator. noise detection means for detecting components outside the band occupied by the data signal included in the electrical signal generated by the amplification means; and a sum of the signal generated by the data signal detection means and the signal generated by the noise detection means. The present invention is characterized by comprising an adder that generates a signal and inputs the signal to the comparator.

[Effect]

The sum of the peak value of the data signal and the value obtained by detecting each of the low frequency components outside the band occupied by the data signal in the electrical signal obtained by demodulating and amplifying the optical signal is calculated. This sum output is compared and amplified with a reference voltage, and the resulting error output is used as a gain control signal for the automatic gain control circuit.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings. 1st
The figure is a block configuration diagram showing the configuration of this embodiment. Components having the same numbers in FIG. 1 as in FIG. 2 are components that perform the same operations.

This embodiment includes a low-pass filter 4, a detector 5, and an adder 16 in addition to the conventional components. That is, as shown in FIG. 1, this embodiment uses an APDl which is a photoelectric conversion means for converting an optical signal intensity-modulated with a data signal, which is a pulse train, into an electric signal, and a signal generated by this photoelectric conversion means. A detector 3 is connected to an optical receiver having an amplifier 2 which is demodulation and amplification means for demodulating and amplifying an electrical signal, and is a data signal detection means for detecting a data signal included in the electrical signal generated by the demodulation and amplification means. , a bias generation circuit 9 that maintains the output level of the opto-electric conversion means within a predetermined range based on a gain control signal, and a data signal included in the electric signal generated by the demodulation and amplification means. A signal that is the sum of the signal generated by the data signal detection means and the signal generated by this noise detection means; The comparator 8 compares the level of the signal generated by the adder 16 with the level of a reference voltage to generate a signal corresponding to the gain control signal of its own circuit.

Next, the operation of this embodiment will be explained.

The output of the amplifier 2 is subjected to peak detection of the pulse waveform by a detector 3, while a low frequency component outside the band of the data signal is extracted from the signal present at the output of the amplifier 2 by a low-pass filter 4. The signal is detected by the detector 5 and sent to the adder 16. The adder 16 adds the outputs of the detectors 3 and 5 and sends it to the low-pass filter 6, and the low-pass filter 6 smoothes the output of the adder 16 and sends it to the comparator 8. . Comparator 8 compares and amplifies the output of reference voltage source 7 and the output of low-pass filter 6, and controls bias generation circuit 9. APDI, amplifier 2, detector 3, adder 16, low-pass filter 4, detector 5, low-pass filter 6, reference voltage source 7, comparator 8, and bias generation circuit 9
The loop is configured to form the same <AGC loop as in the conventional example shown in Fig. 2, and when the optical input signal level to APDI is normal, the components outside the data signal band appearing at the output of amplifier 2 Since it is small compared to the data signal, the output level of the detector 5 is negligibly small compared to the output level of the detector 3, and therefore the loop performs almost the same operation as the conventional example shown in FIG. However, APDI
If the optical signal input to the APD is disconnected or extremely weak,
The noise or microplasma noise due to the dark current of l is amplified by the amplifier 2, so considering that the noise due to the dark current of APDI is mainly white noise and the low frequency component of microplasma noise is large, the noise to APDl is amplified. Compared to the case where the optical signal power level is normal, the ratio of the output level of the detector 5 to the output level of the detector 3 becomes larger,
Therefore, the clock signal level of the noise appearing in the output of amplifier 2 is smaller than that in the conventional example shown in FIG. 2, and the output level of clock extractor 11, which extracts the clock signal component from the output of amplifier 2, is also smaller. The clock interruption detector 12 can stably determine whether the clock is disconnected, and as a result, the prohibition circuit 13 can effectively inhibit meaningless data signals and clock signals.

〔Effect of the invention〕

As explained above, the present invention makes it possible to reduce the clock frequency component included in the demodulated output when the optical input signal is cut off or extremely small, making it easier to detect the clock cut-off, and also to detect the cut-off of the signal when the optical input signal is cut off or extremely small. Alternatively, there is an effect that the output of the clock disconnection detector can stably prevent meaningless data signals and clock signals from being output from the optical receiver when the signal is extremely small.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a block configuration diagram showing the configuration of a conventional example. 1... Avalanche photodiode, 2... Amplifier, 3.5... Detector, 4.6... Low-pass filter, 7
. . . Reference voltage source, 8 . Comparator, 9 . Bias generation circuit, 10 . Inhibition circuit, 14...Data signal output terminal, 15...Clock signal output terminal, 16...Adder. Patent applicant: NEC Corporation, V, ->, Agent: Naotaka Ide, patent attorney

Claims (1)

[Claims] 1. Opto-electric conversion means (1) that converts an optical signal intensity-modulated with a data signal, which is a pulse train, into an electrical signal, and demodulation that demodulates and amplifies the electrical signal generated by this opto-electric conversion means. A data signal detection means (3) connected to an optical receiver having an amplification means (2) and detecting a data signal included in an electrical signal generated by the demodulation and amplification means, and a level and standard of the output of this detection means. a comparator that generates a signal equivalent to the gain control signal of its own circuit by comparing the level of the voltage; and a bias generator that maintains the output level of the photoelectric conversion means within a predetermined range based on the output of this comparator. circuit(
9) an automatic gain control circuit comprising: noise detection means (4, 5) for detecting components outside the band occupied by the data signal included in the electrical signal generated by the demodulation and amplification means; and the data signal It is characterized by comprising an adder (16) that generates a signal that is the sum of the signal generated by the detection means (3) and the signal generated by the noise detection means (4, 5) and inputs the signal to the comparator. automatic gain control circuit.