JPH034645A - Carrier detection circuit - Google Patents

Abstract

PURPOSE:To always attain accurate carrier detection by outputting a binary signal not relating to the amplitude of an input signal to an output terminal from which a signal inverted to a signal at a terminal outputted from a peak value of a 1st comparator is outputted. CONSTITUTION:A received optical signal E is converted into an electric signal F by a photodetector 12, inputted to an input terminal 11a of a comparator 11 and converted into a peak signal H by a peak hold circuit and the peak value of an input signal is kept. The peak signal H is inputted to an input terminal 11b and compared with the electric signal F and a comparison signal I is outputted to an output terminal 11c. The comparison signal I outputted from the comparator 11 is inputted to a filter 16, a high frequency component of the comparison signal I is eliminated and compared with a reference voltage K with the comparator 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a carrier detection (signal detection) circuit used in digital communication systems and the like.

(Prior Art) A conventional carrier detection circuit of this type is shown in FIG.

That is, the carrier detection circuit is composed of two comparators 1 and 2. A signal A shown in FIG. 4(a) is input to the input terminal 1a of the comparator 1,
This signal A is converted into a voltage at a predetermined level by a resistor 3 and is input to a comparator 1. Further, a capacitor 4 and a resistor 5 are connected to the input terminal 1b and the output terminal IC to form a peak hold circuit together with the comparator 1. And with this peak hold circuit,
Input signal A is converted to signal B shown in FIG.
The peak value of the input signal is applied to the input terminal 2a of the comparator 2. The comparator 2 compares this conversion signal B with a reference voltage C applied to an input terminal 2b and shown in (b,) of the same figure, and outputs a carrier detection signal shown in (C) of the same figure from an output terminal 2C. Output.

[Problem to be solved by the invention]

However, in the conventional circuit described above, when the amplitude of the carrier becomes small, it becomes difficult to compare the peak-held signal B with the reference voltage C, and there is a problem that accurate carrier detection cannot be performed. .

That is, as the amplitude level of the carrier decreases, the level of the peak-held signal B decreases, approaching the level of the reference voltage C and competing with it. For this reason, the carrier detection signal, which is the result of comparing both signals, becomes unstable and sometimes oscillates. In order to prevent such a situation, it is conceivable to lower the level of the reference voltage C, but the discrimination sensitivity of the comparator 2 is limited and this is not an effective means of prevention.

[Means to solve the problem]

The present invention has been made to solve such problems, and includes a first comparator that outputs contradictory binary signals corresponding to the comparison results of input signals, one input terminal of the first comparator, and one input terminal of the first comparator. A peak hold circuit that is connected to the output terminal and holds the peak value of the input signal, a filter that is connected to the output terminal that outputs a signal that is opposite to this one output terminal and that cuts off high frequency signal components, and one input terminal. The signal output from this filter is input to the other input terminal, the reference voltage is input to the other input terminal, the signal output from the filter is compared with this reference voltage, and the signal corresponding to this comparison result is determined.
and a second comparator that outputs a value signal.

[Effect]

A binary signal regardless of the amplitude of the input signal is output to the terminal where the peak value of the first comparator is output and the output terminal where the opposite signal is output, and this binary signal is filtered. High frequency components are removed and compared with the fundamental voltage.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment in which the present invention is applied to an optical communication system.

The first comparator 11 has a positive phase input terminal 11a, a negative phase input terminal 11b, a positive phase output terminal 11C, and a negative phase output terminal 11d, and compares the signal levels input to each input terminal 11a and b. , and outputs contradictory binary signals corresponding to the comparison results to the respective output terminals 11e and 11d. The anode of the light receiving element 12 is connected to this input terminal 11a, and this cathode is raised to the power supply voltage. This power supply voltage is set to a predetermined voltage by a resistor 13 connected in series with the light receiving element 12, and is applied to the light receiving element 12. Further, the comparator 11 has an input terminal 11a.
When the signal input to the input terminal 11b is larger than the signal input to the input terminal 11b, a low level signal is output to the output terminal 11c, and a high level signal is output to the output terminal lid.

Conversely, the signal input to input terminal 11a is input to input terminal 11b.
If the signal is smaller than the signal input to the output terminal 11,
A low level signal is output to C, and a low level signal is output to output terminal lid.

One end of a capacitor 14 and a resistor 15 are connected to the input terminal 11b and the output terminal lid, and the other ends of each of these are fixed to a predetermined voltage.

These capacitor 14 and resistor 15 are connected to comparator 1
1 constitutes a peak hold circuit, and holds the peak value of the signal level input to the input terminal 11a.

Further, a filter 16 that blocks high-frequency signal components is connected to the output terminal 11c to which a binary signal opposite to the output terminal 11d is output. The filter 16 is composed of a coil 17 whose one end is connected to the output terminal 11c of the comparator 11, and a capacitor 18 whose one end is connected to the other end of the coil 17 and whose other end is fixed at a predetermined voltage. . Further, the other end of the coil 17 is connected to an input terminal 19a of a second comparator 19.

A reference voltage serving as a reference voltage is applied to the input terminal 19b of the comparator 19, and the comparator 19 compares this reference voltage with the signal output from the filter 16 and generates a binary signal corresponding to the comparison result. It is output to the output terminal 19c. That is, when the signal from the filter 16 is higher than the reference voltage, a low level signal is output, and when the signal from the filter 16 is lower than the reference voltage, a high level signal is output.

In such a configuration, the operation of this circuit will be explained below with reference to the waveform diagram of FIG. 2.

3A shows a pulsed optical signal E as a carrier, and this optical signal E is received by the light receiving element 12. The received optical signal E is converted by the light receiving element 12 into an electrical signal F shown in FIG. At this time, due to the predetermined voltage applied to one end of the resistor 13, the low level voltage of the electric signal F is made slightly smaller than the low level voltage G of the comparator 11, which is indicated by a dotted line in FIG. It is set.

Further, the electrical signal F input to the input terminal 11a is converted by the peak hold circuit into a peak signal H shown in FIG. 2C, and the peak value of the input signal is held. That is, the voltage level output to the output terminal 11d corresponding to the electric signal F is held by the capacitor 14, so that the peak value of the input signal is held. Further, this peak signal H is inputted to the input terminal 11b and compared with the electric signal F, and a comparison signal (2) shown in FIG. 4(d) is outputted to the output terminal 11c. That is, in the illustrated interval T1, the peak signal H is maintained at a constant high voltage level, and this voltage level competes with the voltage level of the electrical signal F. Therefore, the comparison result of both signals is passive, and the comparison signal I
becomes a linear high-frequency waveform. Also, in section T2,
Although the voltage level of the peak signal H decreases slightly, since the electric signal F is at a low level, the comparison signal I becomes a high level signal. Note that since the low level voltage of the electric signal F is set slightly lower than the low level voltage of the comparator 11, the initial state of the comparison signal I is a high level signal.

The comparison signal I output from the comparator 11 is input to the filter 16, the high frequency components of the comparison signal 1 are removed, and the comparison signal I is converted into the low bass signal J shown in FIG.

This low bus signal J is compared by a comparator 19 with a reference voltage shown by a dashed line in FIG.
When the low bus signal J is smaller than the reference voltage, a high level signal is output from the comparator 9. As a result, the output terminal 19c receives the carrier detect signal shown in FIG. (I will be.

As described above, according to the above embodiment, the comparison result by the comparator 11 is a binary comparison signal l that is unrelated to the amplitude level of the optical signal E. Therefore, by removing high frequency components by the filter 16, accurate carrier detection can always be performed regardless of the amplitude level of the optical signal E.

〔Effect of the invention〕

As explained above, according to the present invention, a binary signal regardless of the amplitude of the input signal is output to the terminal to which the peak value of the first comparator is output and the output terminal to which the opposite signal is output. This binary signal is output and its high frequency components are removed by a filter and compared with the base T4Pi voltage.

Therefore, there is an effect that accurate carrier detection can always be performed regardless of the amplitude level of the input signal. In particular, the present invention is effective when applied to carrier detection circuits for highly sensitive optical receivers and carrier detection circuits for attenuated digital electrical signals.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a signal waveform diagram at each part of the circuit of the embodiment shown in FIG. 1, and FIG. 3 is a circuit diagram showing a conventional configuration. , and FIG. 4 are signal waveform diagrams at various parts of the conventional circuit shown in FIG. 3. 11... First comparator, 12... Light receiving element,
13...Resistor, 14...Capacitor, 15...Resistor, 16...Filter, 17...Coil, 18...
- Capacitor, 19... second comparator.

Claims (1)

[Claims] A first comparator that compares the magnitude of the input signal level and outputs a contradictory binary signal corresponding to the comparison result; A peak hold circuit that holds a peak value, a filter that is connected to an output terminal that outputs a signal that is contrary to the first output terminal and cuts off high frequency signal components, and a signal that is output from this filter to the first input terminal. is input, a reference voltage is input to the other input terminal, the signal output from the filter is compared with this reference voltage, and a binary signal corresponding to the comparison result is outputted.
A carrier detection circuit consisting of a comparator and a comparator.