JPS5941343B2 - Binary code DC feedback method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a binary code DC feedback system that performs DC compensation necessary for decoding on the receiving side of binary codes such as optical signals where a signal exists only on one side with respect to a reference value. It is.

To explain further, in binary code (1, o level) transmission, in order to judge the binary code, the average value of the 1, 0 level is always at the center of the 1, 0 level, and the binary code is judged. This is a method that ensures that this is done.

In the conventional method, the binary code is integrated over a long period of time, and the average value is taken as the DC level.

In this case, it was necessary that the binary code itself be encoded so that it has an equal probability of occurrence at the 1 and o levels. However, the mark rate of the binary code is not necessarily maintained at 50%, and is 1, 1, 1, etc.
In many cases, binary codes such as o, o, etc. are transmitted. In such a case, especially if the mark rate of the binary code is 5
Encoding processing was performed so that the value became 0%. In order to solve the above-mentioned difficulties, the present invention provides a binary code direct current feedback system that can judge binary codes regardless of the probability of occurrence of the mark rate of the binary code using a circuit mainly composed of an AGC and a peak detection circuit. It is something to do.

The present invention will be explained using diagrams taking an example of optical transmission.

FIG. 1 is for explaining the outline of the present invention. 1
is a light emitting diode, 2 is a photodiode (light receiving element),
3 is power supply, 4 is current voltage conversion, 5 is AGC, 6 is AGC
T is the V+ output terminal of the AGC, 8 is the peak detection circuit, and 9 is the feedback output of the peak detection circuit.

Figure 2 is a diagram for explaining the basics of the present invention, and shows the difference in the center level of the same polarity (V+) and opposite polarity (V-) of the binary code.
It is a conceptual diagram for making V zero.

Here, V+ indicates 1 when the level is 1 and indicates 0 when the level is 0, and V- indicates O when the level is 1 and indicates 1 when the level is 0. FIG. 3 shows an embodiment of the peak detection circuit of the present invention.

11 is a V- input terminal, 12 is a V+ input terminal, T, l
, T,2, T,4, T,5 are transistors, T,3 is a constant current source transistor, A, B are points indicating potential, C is a capacitor, Rl, R2 are resistors, β is a transistor of T,5. Current amplification factor, +V indicates power supply.

In FIG. 1, optical signals 1 and 0 from a light emitting diode are received by a photodiode (light receiving element) 2, and a photoelectric conversion output is input to a current-voltage conversion circuit 4, and the output is sent to an AG.
C5, and the output terminals 6 and 7 output V-1+ as shown in FIG.
The peak detection output is fed back to the current-voltage conversion circuit in order to create a center level.

Figure 3 describes peak detection and DC feedback.

This circuit, into which the outputs V- and V+ of the AGC 5 are input to input terminals 11 and 12, basically consists of a comparator and a peak voltage holding circuit. The comparator is T,l~
It is composed of T and 3, performs the calculation of (V--+), and its maximum value is held in the capacitor C1. (V-1V+
) is positive, capacitor C1 is charged with the time constant of R1・C1, and when (V-1V+) is negative, β・R2・
Large time constant of C1 (β・R2・C1〉〉R1′C1)
The voltage is discharged in a slow period of time, and DC feedback is returned to the current-voltage conversion circuit 4 from the terminal R2, bringing ΔV close to zero. Next, when V- and V+ are crossed over as shown in Figure 4, when the level at point a above V- is input to the input terminal 11 in Figure 3, V- becomes high and T ,l operates,
T,2 stops operating, the potential at point A rises, T,4 operates, charges C1 with the time constant of R1・C1, and charges the charge potential (potential minus Vbe of T,5). Return.

Conversely, when V+ becomes low, the same operation is performed so that the level at point b becomes zero.

This makes the crossover ΔV zero. As described above, the present invention operates only at the closest portions of V+ and V-.

Therefore, it has the advantage that it is not affected by signal vibration and can operate independently of AGC.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an overview of the present invention, FIG. 2 is a diagram showing the basics of the invention, FIG. 3 is a diagram showing a peak detection circuit of the present invention, and FIG. 4 is a diagram showing the peak detection circuit of the present invention. A diagram showing a cross-over is shown. In the figure, 1 is a light emitting diode, 2 is a photodiode, 3 is a power supply, 5 is AGD, 7 and 8 are V- and V+ output terminals, V+
indicates the same polarity, and V- indicates the opposite polarity.

Claims (1)

[Claims] 1. In a system that transmits information using a binary code in which a signal exists only on one side with respect to a reference value, a circuit that generates signals of the same polarity and opposite polarity as the input signal, and the levels of the same and opposite polarity signals. and a peak value detection circuit that detects the peak value of the difference, and feedback is applied to the output of the peak value detection circuit so that the lowest value of the same polarity signal and the maximum value of the opposite polarity signal (or vice versa) match. A binary code DC feedback method characterized by: