JPH01226216A - Carrier detecting circuit for optical receiver - Google Patents

Abstract

PURPOSE:To detect the carrier of a signal which a light-emitting element has received without hourly shift by amplifying a signal the light-emitting element has received in a reverse amplifier and comparing an envelope detection waveform which is obtained by envelope-detecting the output of the reverse amplifier in a comparator with a reference voltage. CONSTITUTION:A pre-amplifier 12 consists of the reverse amplifier 3, a feedback resistance 2 and a capacitor 11, and the cathode of the light-emitting element 1 is connected to the input terminal of the reverse amplifier 3 through the capacitor 11. The connection point of the capacitor 11 and the light-emitting element 1 is connected to one of the input terminals of the comparator 8, and a signal Ve inputted to the input terminal is compared with the collation voltage Cref. The input signal Ve of the comparator 8 comes to the waveform in which the lower limit of an output signal Vd of the pre-amplifier 12 is envelope- detected and furthermore, rise after carrier termination is steep. Consequently, the output signal Vf of the comparator 8, which is the comparison result of the signal Vd and the collation voltage Vref, hourly coincides with the presence or absence of the carrier and complete carrier detection is attatined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a carrier detection circuit for an optical receiver used in an optical communication system or the like.

[Conventional technology]

FIG. 6 shows a carrier detection circuit of a conventional optical receiver. Light emitting element 1 such as a photodiode
The received signal converted into an electrical signal is input to a peak hold circuit 10 via a preamplifier 9. Figure 7 (A
) is the waveform of the output signal V of the preamplifier 9, and the period T
There is no carrier in section T1 and T2, and there is a carrier in section T3. The output signal Vb of the peak hold circuit 10 is given to one input terminal of the comparator 8,
There, it is compared with the reference voltage V.

ef FIG. 7(B) shows the output signal V of the peak hold circuit 10.
, and the reference voltage V is shown by the - dotted chain line b
ref' is there. As shown in FIG. 4C, if the input signal Vb of the comparator 8 is larger than the reference voltage Vrer, its output becomes high level, and if it is smaller, the output becomes low level. Therefore, the output V of comparator 8. If it is at a high level, it means that there is a career, and if it is at a low level, it means that there is no career.
Carrier detection is achieved. The preamplifier 9 includes an inverting amplifier 3 and a feedback resistor 2, and the peak hold circuit 10 includes a comparator 5, a resistor 6, and a capacitor 7.

[Problem to be solved by the invention]

However, in the conventional circuit described above, since the time constant due to the resistor 6 and capacitor 7 in the peak hold circuit 10 is large,
The fall of the output of the peak hold circuit 10 is delayed. Therefore, as shown in section T4 in FIG. 7, the output of the comparator 8 remains at a high level even though there is no carrier, and there may be a problem that the output appears as if a carrier is present. Ta.

An object of the present invention is to solve these problems.

[Means to solve the problem]

In order to solve the above problems, the carrier detection circuit of the present invention includes a photodetector whose one terminal is AC grounded, a capacitor whose one end is connected to the other terminal of the photodetector, and a capacitor whose one end is connected to the other terminal of the photodetector. an inverting amplifier having an input terminal connected to its other end; a feedback resistor connected between a connection point between the capacitor and the light receiving element and an output terminal of the inverting amplifier; and a connection between the capacitor and the light receiving element. A comparator having a point connected to one input terminal and a reference voltage applied to the other input terminal.

[Effect]

The signal received by the light emitting element is amplified by an inverting amplifier, and a waveform resulting from envelope detection of the output of the inverting amplifier appears at the connection point between the capacitor and the light receiving element. This envelope detection waveform is then compared with a reference voltage by a comparator. Since this envelope detection waveform quickly follows the output result of the inverting amplifier, the comparison result by the comparator has almost no temporal deviation from the presence or absence of a carrier in the signal received by the light emitting element.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention. Note that in the drawings, the same elements are given the same reference numerals. In this embodiment, the preamplifier 12 is composed of an inverting amplifier 3, a feedback resistor 2, and a capacitor]1, and the cathode of the light emitting element 1 is connected to the inverting amplifier 3 via the capacitor 1.
is connected to the input terminal of And capacitor 1
The connection point between the light emitting element 1 and the light emitting element 1 is connected to one input terminal of the comparator 8, and the signal 2 input thereto is compared with the reference voltage V2.

e ref FIG. 2 shows the operation waveforms of this embodiment, and shows the case where the same signal as the signal in the operation explanation of FIG. 7 is received so that the operation can be compared with the operation of the conventional circuit. FIG. 2(A) is a waveform diagram showing the output signal Vd of the preamplifier 12, which is similar to the output signal Vd of the preamplifier 9 in the conventional circuit in the interval T1.
There is no carrier in section T2, and there is a carrier in section T3. As shown in FIG. 3B, the potential at the connection point between the light-emitting element 1 and the capacitor 1, that is, the input signal (■) of the comparator 8, has a waveform obtained by envelope detection of the lower limit of the output signal Vd of the preamplifier 12, and ,
His rise after the end of his career was steep. Therefore, the output signal Vr of the comparator 8, which is the comparison result between the signal V6 and the reference voltage ■, coincides with the presence or absence of a carrier in time, as shown in FIG. achieved.

Note that FIG. 3 shows a specific circuit of this embodiment, in which the inverting amplifier 3 is composed of resistors 20, 21, 23, 26, a field effect transistor 22, a capacitor 24, and an npn
) transistor 25.

FIG. 4 is a circuit diagram showing another embodiment of the present invention, and FIG.
The figure shows its operating waveform diagram. In the above-mentioned embodiment, the anode of the light emitting element 1 is grounded in an alternating current manner, but in this embodiment, on the contrary, the cathode of the light emitting element 1 is grounded in an alternating current manner.

With this connection, the output signal V' of the inverting amplifier 3
has a waveform as shown in FIG. 5(A), and the input signal V' of the comparator 8 becomes the signal V', as shown in FIG. 5(B).
It is obtained by envelope detection of the upper limit of , and shows a steep fall at the end of the carrier as in the previous embodiment. This signal is compared with a reference voltage V, giving an accurate carrier detection output v' as in FIG. 2ef (C).

(Figure 2 (C)).

〔Effect of the invention〕

As described above, according to the carrier detection circuit of the present invention, the carrier of the signal received by the light emitting element can be detected without temporal shift. Therefore, the carrier detection circuit of the present invention is extremely effective when used in an optical receiver that requires accurate carrier detection. Furthermore, since the peak hold circuit required in the conventional carrier detection circuit can be omitted, the overall circuit configuration can be simplified, which is effective in reducing costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is an operating waveform diagram thereof, FIG. 3 is a circuit diagram showing this embodiment in more detail, and FIG. 4 is a block diagram showing another embodiment of the present invention. FIG. 5 is a circuit diagram showing an embodiment, FIG. 5 is an operating waveform diagram thereof, FIG. 6 is a block diagram showing a conventional optical receiver, and FIG. 7 is an operating waveform diagram thereof. DESCRIPTION OF SYMBOLS 1... Light emitting element, 2... Feedback resistor, 3... Inverting amplifier, 8... Comparator, 11... Capacitor. Patent applicant: Sumitomo Electric Industries, Ltd. Representative patent attorney Yoshiki Hase
Salt 1) Tatsuya■
Result ≧ 1 Mountain 0 No. 19 The customary Gurei's Roro path Fig. 3 Other examples Fig. 4 Movement A year waveform Fig. 5 Recommended thousand wave form of the Jusong branch technique

Claims (1)

[Claims] A light receiving element whose one terminal is grounded in an alternating current manner, and a capacitor whose one end is connected to the other terminal of this light receiving element.
an inverting amplifier having an input terminal connected to the other end of the capacitor; a feedback resistor connected between a connection point between the capacitor and the light receiving element and an output terminal of the inverting amplifier;
A carrier detection circuit for an optical receiver, comprising: a comparator having one input terminal connected to a connection point between the capacitor and the light receiving element, and a reference voltage being applied to the other input terminal.