JPS59189752A - Digital optical receiver - Google Patents

Abstract

PURPOSE:To operate stably a digital optical receiver for an optional binary code system even in a high bit rate by using an AC coupling amplifier and a comparator provided with a positive feedback circuit which has the same time constant of response as that of base level variance due to DC cut-off of the AC coupling amplifier. CONSTITUTION:If reception is started when the level for no signal of an AC coupling amplifier 12 and an average level of high and low level outputs of an inverting gate 7 are equal to each other, the base level of an output 12a of the AC coupling amplifier 12 starts falling; but since a discrimination threshold 6a falls with the same time constant, a well received and reproduced comparator output 4a is obtained. A feedback circuit 14 does not require quick response and is operated normally even in a high bit rate. Even if a waveform distortion is generated in a transmission line or the AC coupling amplifier, it is difficult that receiving and reproducing errors are generated because waveform conversion such as differentiation or the like is not performed. Even if receiving and reproducing errors are generated, the influence of these errors upon another bit can be ignored unless they continue for a long time of the approximate time constant of the feedback circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital optical receiver that receives and reproduces binary digital optical signals.

FIG. 1 shows a configuration diagram of a conventional digital light-speed receiver. In FIG. 1, (11 is a light receiving element, (21 is an i+
:4: Current coupling amplifier, (31 is a differentiating circuit, (4) is a comparator, (51 is a signal input terminal, (6) is a judgment threshold value, (71 is an inverting gate, (approx. is a wholesaler circuit) , (9) and (101 are resistors, and (11+ is a reference voltage.
la) is the reception) symbol, (2a) is the amplifier output 1
No. 5, (3g) is the differential waveform, (4a) is the ratio result signal, (6a) is the judgment threshold I signal, (7
a) shows the inverted gate output signal, and '(Ila) shows the reference voltage source voltage signal.

The light receiving element (11 photoelectrically converts the received optical signal (IN).

The DC amplifier +21 amplifies the input from the light receiving element (11) and outputs a small signal (2a) to the differential circuit +31.The signal (2a) is output to the DC coupled amplifier (21). is finite, so the waveform becomes dull.The differential circuit (31 is a single current amplifier (21)
Differentiate No. (2a) [.

The differential waveform (3a) is input to the signal input terminal (51) of the converter (4).
Output to.

Ratio softener (41 is a differential circuit (signal input from 31)
a) and the temporary terminal that has been judged as 1 for a long time (input to 61?I'(
The comparison result signal (4a) is outputted as the comparison result signal (4a). β).Feedback circuit (βlVi resistor (9) and
11 (quasi-voltage source (111) consisting of 9 inverting gates (7
The output of 1 is divided into voltages, judged by a comparator, and output to the A value terminal +61. Here *l! Differential circuit (3
1 of 1i! t jt level and 1 inversion gate (7)
High level output Vl+ and low level output V1. Let us explain the case where the average level of is equal to [,. Reference voltage source (1
Voltage (lla) of 11 is set to k T (VII + VL), resistor (9) and resistance value R1 of 4 (resistance value R1, 112 is the center VC-r11 of the output signal of 31) So that (6a) matches.

Set the value trc to add -1. However, vo is differential 1! : 11 road (zero-beak value of 31. At this time,
Feedback by the signal feedback circuit (81) causes a hysteresis characteristic in the comparator (41).As shown in Figure 2, this hysteresis characteristic allows for better signal regeneration than in the digital optical receivers k and 11. .This operation can be performed regardless of the A or J format of the signal.

Since the conventional optical transmitter/receiver uses a differentiating circuit (3), there may be cases where there is K distortion in the receiving 4M (]II) or where distortion occurs in the @flow coupling amplifier (21). , the image width of the differential output (3a) fluctuates, and there is a drawback that reception and reproduction errors are likely to occur due to the occurrence of code amount interference, etc. This drawback becomes more noticeable as the bit rate becomes higher.

In addition, comparator (4) 1 inverting goo [71, feedback circuit (81
The feedback M must be fed back within one bit, and a high bit rate requires a high speed feedback circuit.

You can also receive playbacks if you fall asleep.

Since erroneous feedback is applied, there is a drawback that reception and reproduction errors may spread to other bits.

In order to eliminate these drawbacks, the present invention uses an AC coupled amplifier instead of a differentiating circuit.

Give a time constant to the feedback circuit that feeds back the comparator output.

The time constant is set to be equal to the signal base level fluctuation time constant due to one current cutoff of the fully AC coupled amplifier, and will be described in detail with reference to the drawings below.

It is a circuit.

The light receiver (1) converts the received signal (1a) into a light beam and outputs it to the 111-amplifier (121).

Amplify the input signal from the light receiving element (11) and convert it to a comparator (4)
Output No. 44 (12a) to. The ratio 1 terminal (4) is the signal (12a) input to the signal input terminal (51) and the determination threshold signal (12a) input to the terminal 11 (61).
6a) 117 comparison and outputs a comparison result signal (4a). The inversion gate (71 is the comparison result of the ratio 1 ash unit (4)
llJl, :ydenza+131, reference voltage source 0
1) is output to the feedback circuit (14i).The judgment threshold (6a) has one end connected to the inverting gate (71) and the fc resistor (91), and one end connected to the reference voltage source (11). resistance (101).

A capacitor with one end grounded (common connection point of 131 and judgment threshold 111J of comparator (4), terminal 161'k
Get connected.

Here, for a simple fc, the level of the AC coupled amplifier (121 when no signal is present) and the inverting gate (high level output Vl of 71)
, and low level output v1. The case where the average level of is equal to the average level will be explained.

As before, the voltage of power supply Qll is +(VH+VL)
and the resistance value R1+ of resistors (9) and (101)
R2 is set to satisfy Equation 11.The capacitance of the capacitor (1j1 is set when the base level fluctuation time constant τ of the signal due to the DC connection of 91 is for the feedback circuit; The value is set to k n & B plus to match the constant. When reception starts.

As shown in Fig. 4, the output (1
The base level of 2a) begins to fall, but the judgment threshold (
6a) also falls with the same time constant, so it is possible to obtain the comparator output (4a)k which has been well regenerated. Further, this operation can be performed on signals of any code format. Feedback circuit east does not require a fast response and works well even for high bit rates.

Furthermore, even if waveform distortion occurs in the transmission line or AC coupling amplifier, reception and reproduction errors are less likely to occur because differential-only waveform conversion is not performed. Furthermore, even if a receiver error occurs, the spread of the error to other bits can be ignored unless it continues for a long time, about the time constant of the # return circuit (!41).

Note that 2 or more is an AC coupled amplifier (1) assuming that the output level when no signal of I21 is equal to the average level of the output of the inverting gate (71), but in other cases, the resistance (91°t
A similar operation can be achieved by adjusting the resistance value of llll and the power supply voltage of the reference voltage source (11).

I cut it. In a specific absorber having positive-phase and negative-phase output terminals, the same operating noise can be obtained even if +71 is not used and the negative-phase output is connected to the feedback circuit.

As described above, the digital optical receiver according to the present invention uses an AC coupled amplifier and a comparator having a positive feedback circuit with a response time constant equal to the base level fluctuation time constant caused by blood flow transection in the AC coupled amplifier. Even at high bit rates, it has the advantage of being able to operate stably for any two provisional encoding formats.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional digital optical receiver. FIG. 2 is a waveform diagram of each part of a conventional digital optical receiver, and the third factor is 4'? of an embodiment of the optical receiver according to the present invention. FIG. 4 is a waveform diagram of each part of the optical receiver according to the present invention. In the figure, (4) is a comparator, (7) is an inverting gate, total is an AC coupling amplifier, and fli is! This is an Ifl return circuit. Also in Figure 1. Identical or similar parts are designated by the same reference numerals. Agent Masu Oiwa 1 Figure 1 Figure 2 Figure 13 Diagram 4

Claims (1)

[Claims] 2 (1i1- In a digital optical receiver that receives a digital optical signal, an AC coupling amplifier connected to a light receiving element output terminal and the output of the AC coupling amplifier are compared with a determination threshold value to reproduce a 2' It+ digital signal. A comparator that inverts the output of the comparator, an inversion gate that inverts the output of the comparator, and a response 111 that is equal to the signal base level installation time constant due to the DC connection of the AC coupling amplifier, and the circuit comparator is determined by -nr1; What is claimed is: 1. A digital pre-reception A Δ device comprising a feedback circuit that feeds back to a threshold input.