SU1725368A1 - Optosignal demodulator - Google Patents

Abstract

The invention relates to a pulse technique and can be used in processing systems and generating pulse signals of a photosensor. The purpose of the invention is to increase the noise immunity - achieved by introducing a splitter 2 frequency, two D-flip-flops 4 and 5, a coincidence element 9, a control bus 10, an interface 8. The demodulator of optical signals also contains a generator of 1 clock pulses, a driver of 3 clock pulses, a buffer element 6, a photo detector 7. 2 Cp. f-ly, 1 ill. .

Description

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The invention relates to a pulse technique and can be used in processing systems and generating pulse signals of a photosensor.

The purpose of the invention is to improve noise immunity.

The drawing shows an electrical functional circuit diagram of the device.

The optical signal demodulator contains a clock pulse generator 1, a frequency divider 2, a clock generator 3, two D-flip-flops 4 and 5, a buffer element 6, a photodetector 7, an interface 8, a coincidence element 9, a control bus 10 and an output bus eleven.

The output of the 1 clock pulse generator is connected to the clock input of the splitter 2 frequency, the inverse output of which is connected to its D input and C input of the D flip-flop 4, direct output to the first input of the forcing device 3 sync pulses, and the R input with a bus The 10-control, S-inputs of 0-flip-flops 4 and 5 and the second input of the synchronization generator 3, the output of which is connected to the first input of the coincidence element 9 and the D-input of the D-trigger 4, the inverse output of which is connected to the second input of the coincidence element 9 and the control the input of the buffer element 6, the information input which is connected to the Power bus and the photodetector input 7, and the output to the photodetector 7 output and through the interface 8 interface to the D input of the D flip-flop 5, the C input of which is connected to the output of the coincidence element 9, and the output to the output bus 11 devices.

Shaper 3 sync pulses contains an OR-NO 12 element, the output of which is connected to the output of the imaging unit of 3 sync pulses, and inputs to the corresponding outputs of the counter of 13 pulses, the C input of which is connected to the first input of the imaging unit of 3 sync pulses, and the R input with its second input .

The demodulator works as follows.

In the initial state, the generator 1 and the frequency divider 2 continuously operate, which forms two clock signals T1 and T2. On the bus 10 of the device, a high level of Log.1, which prohibits the operation of the imaging unit 3 (and blocks 2 and 4), at its output a low signal level of Log.O, as a result, under the action of the clock pulses T2 of the trigger 4, the inverse output has a high level log.1. At the inputs of element 9 there are different levels of voltage: the first input is Log.O, the second input is Log.1 and, as a result, the output is Log.O. Under the influence of high level

the signal from the output of trigger 4 to the control input of buffer element 6, the latter is in the open state, its direct resistance from the input to

the output is 100 Ohms, and the supply voltage + En is almost entirely applied to the output of the photodetector 7, the output of the latter is a high level of Log.1, i.e. connected to the load of the photodetector 7

low impedance ph2 of 100 ohms, this load determines all the main characteristics of the demodulator. At the output of the interface block 8, a level of Log.1 is set. At the same time, the high level of the original signal from bus 10 is fed to the S input of the D flip-flop 5, as a result of which the level of Log.1 is set at the device output. A high level of Log.1 over bus 10 is a signal to the initial setup of the device.

When a light signal S (t) appears in the optical input of the photodetector 7, a photocurrent f occurs in the latter, but the output voltage at its output will be close to

zero, i.e. Signal 1 will remain high. Changes in the level of the information signal on the RH will be so insignificant that it can be neglected. As soon as on the bus 10 of the device, the demodulator turns on at a low level of control voltage. Immediately the shaper of 3 sync pulses will start to work, and at its output a short pulse of duration g and with a period of TK

which is ten times less than the duration of the pulse of the light signal mc. The signal obtained in the imaging unit 3 is fed to the D-input of the trigger 4 and to the input of the element 9 by a high level Log.1 with a pulse duration t, and with the appearance of the next edge of the pulse T2 from the output of the frequency divider 2, the pulse with a duration g is triggered 4 its inverse output appears a low signal level, which is fed to the input of the coincidence element 9 and to the control input of the buffer element 6; the latter closes and its output resistance becomes high resistance. At the output of the photo detector 7

on Wits Log.O level information signal, which goes to the D-input of the trigger 5. At the S-flip-flop input on the Wits Log.O level of the enabling signal Uynp- At the D-input of the trigger 4, the Log.O signal is low, which also entered the input element 9 matches. At the two inputs of element 9 there are low levels of Log.O, at the output of the voltage drop across the voltage from Log.O to Log.1 - a signal was received at the front of the recording pulse, which goes to the clock trigger input 5 and records the information signal from the block output 8 interfaces per trigger 5. At the output of the device, the information signal Log.0 lows. Next, the next T2 cycle (drop of T1 signal) triggers reset to its initial position, a high level of Log.G appears at its inverse output, which activates the buffer element b and a high level of Signal appears on the detector bus 11. one. The value of the photocurrent in the equivalent load of the photodetector will remain the same. After time Tp, the photodetector 7 will be turned on again, etc. many times.

Due to the fact that instead of the presence at the input of the photodetector 7 of a signal of long duration, on. its output is constantly present at a high frequency signal, as if its constant signal is fragmented into very small signals with a short duration over a period — meaning that the pulse ratio is large. Then the 1 / F noise level will also decrease, while the white noise value will drop at the same time, which can be determined by the formula

 / (HBx (uO) 2d.

Rh

In j

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where K is a constant Boltzmann,

in - absolute temperature;

Hin (o) is the transfer function of the input circuit;

w - angular frequency;

Tm is the signal noise power.

Obviously, the longer the duration

input signal (more than a duty cycle 0) tf,

the longer the pause Tp, the smaller

signal noise ish. So, with the ratio

B / Tp is equal to 0.1, the noise power Tsh is reduced six times. It is easy to calculate it by the formula, if you take the ratio Q 10, at which T - 10to and F increases, this means that with the expansion of the demodulator transmission band, the amplitude of thermal noise increases. Therefore, it is desirable to have a signal at the input with a low frequency. It would seem that this led to an increase in the type 1 / F noise, however, this does not occur, since the duration of the signal's reference time is rather small at the maximum sensitivity of the demodulator, and the pause between readings is large at almost zero sensitivity of the device. Therefore, the weight 0 5

0 5

0

five

0

.

The possibility of noise in the pauses is negligible.

If the duration of the information signal ts is longer than the duration of the TZ, then it is obvious that, the shorter the duration of the TZ, the 1 / F type noise will be reduced by the same amount of time.

Produced M times the gating of the signal (t) at the output of the photodetector, we obtain respectively the same M1 pulses Uc with the parameters to and Tn, which further hitting the trigger 5 are expanded last to the duration of the TC ± TP (M M1) of the light pulse.

If a low level of the photodetector 7 appears at the Optimum input (its absence), the output level will be Log.1 at all times. Regardless of the state of element 6, it will periodically confirm the output state of the photodetector 7. When the trigger output 5 is set to high level Log.1, corresponding to the absence of an information light signal. When a new light pulse appears at the device input, the operation of trigger 5 and block 8 is repeated.

The optical signal demodulator can also be used to process analog signals, for which it is necessary to change the construction of the interface block 8 so that it divorces the photodector 7 with subsequent cascades, and instead of the trigger 5 it can use an analog-to-digital converter, while ensuring all necessary control signals. In this case, the information at the output of the device is represented in the form of a binary code and displays the nature of the change in the luminous flux at the input of the photodetector 7.

Claims (3)

Claim 1. An optical signal demodulator containing a photodetector, a clock generator, a clock generator, a buffer element, the output of which is connected to the photodetector output, and an output bus, characterized in that, in order to improve the noise immunity, a frequency divider, two D-flip-flop, control bus, matching element and interface block, the clock pulse output is connected to the clock input of a frequency divider, the inverse output of which is connected to its same D input and C input a first D-flip-flop, a direct output - with an input of the first clock, a second input coupled to the control bus and S-input of the second D-flip-flop, and output to the first input of the match element and D-input of the first D-flip-flop, the inverse output of which is connected to the second input of the match element and the control input of the buffer element, the information input of which is connected to the Power bus and input a photodetector, the output of which, through the interface block, is connected to the D-input of the second D-flip-flop, the C input of which is connected to the output of the matching element, and the output to the output bus of the device. 2. The demodulator according to claim 1, from the left side so that the driver is a sync pulse The owl contains a pulse counter, the clock input of which is connected to the first input of the sync pulse generator, the R input to the second input of the sync pulse generator, and the outputs to the corresponding inputs of the OR element, the output of which is connected to the sync pulse generator output. 3. The demodulator according to claim 1, exe and so that in order to increase accuracy with increasing frequency of signal processing, the R-input of the frequency divider is connected to the S-input of the first D-flip-flop and control bus.