SU773953A1 - Device for demodulating frequency-modulated signals - Google Patents

Description

one

The invention relates to engineering. transferring discrete information and can be used in building signal conversion devices .5

A device for demodulating frequency-modulated (4M) sig. low carrier ratios. frequency to modulation frequency, containing a series-connected band-pass filter, a limiter amplifier, a signal edge extraction unit, a first counter, a first envelope selection unit, a control unit, and an j-generator, the output of which is connected to the first input of the signal generator the second input and output of which are connected respectively to the output of the frequency divider and the first input of the coincidence unit, to the second input of which the output of the first counter is connected, the second input of which is connected to the second input of the controlled eratora, the input of the frequency divider 25 output a high-frequency generator and the first input of the second counter, the outputs of which are connected respectively to the third input of the first counter and the first block entry eliminated LP

2

not crushing, the output of which is connected to the second input of the signal edge selection unit, the output of which is connected to the second inputs of the second counter and the crushing block, and the output of the coincidence unit is connected to the second input of the control unit.

However, the known device has a low noise immunity.

The purpose of the invention is to improve noise immunity.

This goal is achieved in that a device for demodulating frequency-modulated signals at a low carrier-to-modulation frequency ratio, comprising a series-connected band-pass filter, a limiting amplifier, a signal edge extraction unit, a first counter, a first envelope selection unit, a control unit and a controlled oscillator, the output of which is connected to the first input of the signal generator, the second input and output of which are connected respectively to the output of the frequency divider and the first input of the coincidence unit, to toromu input of which is connected the output of the first counter. the second input of which is connected to the second input of the controlled generator, the input of the frequency divider, the output of the high-frequency generator and the first input of the second counter, the outputs of which are connected respectively to the third input of the first counter and to the first input of the crushing block, the output of which is connected to the second input of the front separation unit the signal, the output of which is connected to the second inputs of the second counter and the crushing block, and the output of the coincidence unit is connected to the second input of the control unit, the third meter is entered etchik, elements AND, two trigger elements OR, and a second selection block of the envelope, the outputs of which are connected to the first inputs of the corresponding, elements AND, the second inputs and outputs of which are connected respectively to the first output of the third counter and the first inputs of the elements OR, to the second inputs of which are connected the third and third outputs of the third counter, while the outputs of the OR elements are connected to the inputs of the first trigger, the outputs of which are connected to the first inputs of the corresponding elements AND, the second inputs of which are connected to the additional the output of the controlled generator and the first input of the third counter, the second input of which is connected to the output of the signal edge selection unit and the first input of the second envelope selection unit, the second input of which is connected to the additional output of the first counter, and the outputs of the corresponding elements are connected to inputs of the second trigger. The drawing shows the structures on the electrical circuit of the device. The device for demodulating the FM signal contains a band-pass filter 1, an amplifier-organizer 2, a block for separating the signal front, a block 4 for crushing devices, the first counter 5, the second counter 6, the high-frequency generator 7, the first block 8 of the envelope, controlled generator 9, signal generator 10, frequency divider 11, coincidence unit 12, control unit 13, third counter 14, element OR 15, first trigger 16, element OR 17, second envelope allocator 18, elements AND 19-22 second trigger 23. The device works as follows. The FM signal received from channel cb zi is limited by the spectrum by a common filter 1 and by amplitude by a limiter 2 and fed to the input of the block 3 of the front separation c, the signal producing short pulse gates (zero intersections the occurrences of which coincide with the transition moments FM signal at zero level.When a hub intersection is selected, block 4 eliminates crushing including blocking the reception of zero intersections at time S. At the same time, zero crossings from the output of block 3 of the fron signal are sent to the first The second counter 5 and the second counter 6, the BTOPQ I and the first inputs of which receive impulses f from the high-frequency generator 1, respectively. When the second counter b is set to the state corresponding to the end of blocking E, a second signal is generated at its second output crushing removes the blocking from the block of the signal front block 3. At the time points corresponding to zero intersections of the FM signal, the measurement result of the current half-loop from the second counter 6 is transferred to the first counter 5, which is independently ibavl to this value is the result of measurement of the next half cycle of the FM signal. As a result, the result accumulated in the first counter 5 at each time of the occurrence of zero intersection displays the duration of the current period of the FM signal by the number of pulses of the high-frequency generator 7. To select an envelope by the duration of the period of the FM signal, the signal from the output of the first counter 5 enters the envelope extraction unit 8. The controlled generator 9 generates synchronizing pulses that start the generator of 10 signals, taking into account the initial shift of the reference point, equal to the ratio of the frequency fgi of the high-frequency generator 7 to the characteristic frequency f corresponding to symbol 1. Pulses are received from the second input of the generator 10 of signals that divides the frequency fg of the high-frequency generator 7 by a factor equal to the ratio of the characteristic frequency f- (to twice the frequency deviation 24f (2if about f 1 D fo and f 1 is the character the initial frequencies are, respectively, for symbols O and 1). The output of the signal generator 10 is connected to the first input of a matching block 12, the second input of which is connected to the output of the first counter 5. A matching block 12 performs a time-continuous comparison of the duration of the FM signal period with the current value of the number B the signal generator 10. The output of the coincidence unit 12 is connected to the second input of the control unit 13, the first input of which is connected to the output of the envelope video block 8.

If during the duration of the period of the FM signal by the block 12, the equality of the values of the numbers coming from the first counter 5 and the signal generator 10 is fixed, then the control block 13, if there is an envelope selection of the signal envelope, has the moment corresponding to switching from the characteristic frequency f to the frequency f, reduces the frequency of the pulses of the controlled oscillator 9, providing an adjustment of the clock pulse to the ideal significant moments.

If during the duration of the period of the FM signal by the block 12 matches the equality of the values of the numbers coming from the first counter 5 of the signal generator 10 is not fixed, the control block 13, if the envelope of the signal envelope has a significant moment corresponding to the switch from the characteristic frequency f to the frequency fd, increases the frequency of the pulses of the controlled oscillator 9. In this way, the magnitude of the phase mismatch between the ideal significant positions and the synchronizing pulses is reduced.

The reconstruction of the FM signal envelope is carried out as follows.

The third counter. 14 performs a time-continuous counting of zero intersections arriving at the second input from block 3 of the signal fronts between two adjacent clock pulses.

If the third counter counts between two synchronizing pulses the number of zero crossings, which basically belongs only to the characteristic frequency f, then the signal from the third output of the third counter 14 through the OR 15 element first trigger 16 is set to the state corresponding to the reception of the significant position 1.

If the third counter 14 counts between two synchronizing pulses the number of zero intersections which basically belongs only to the characteristic frequency f, then the signal from the second output of the third counter 14 through the element OR 17 first trigger 16 is set to the state corresponding to the reception of the significant position O.

If the third counter 14 counts between two sync pulses the number of zero intersections, which is obtained when receiving the characteristic frequency fg and frequency f, then the signal from the first output of the third counter 14 on the element 19 and the element 20 also analyzes the state of the second selection block 18 the envelope that sets the state

or 1, based on the condition that the phase mismatch of each of the characteristic frequencies of the FM signal is the same, and some asymmetry of the loss of some information about the signal at different significant positions, low carrier frequency to modulation rate and digital processing of the FM signal is eliminated due to the shift of the boundary of the zone, with which the estimated size of the FM signal is compared (the duration of the analyzed half-periods), in the direction of its slight increase.

If the second block 18 of the envelope selection is fixed

15 position corresponding to 1, when forming a signal at the first output of the third counter 14 by a signal from the output of the element 20, the first trigger 16 is set to

0 1 If a significant position corresponding to O is fixed at the second output of the second envelope extracting unit 18, then when forming the sig,. On the first output of the third counter 14, the signal from the output of the element I 19 of the first 16 trigger is set to O.

The state of the first trigger 16 by the clock pulses of the controlled oscillator 9 is rewritten through the elements 21 and 22 to the second trigger 23.

At the output of the second flip-flop 23, a sequence of received single elements is formed.

5 Taking into account the fact that this device for demodulating FM signals eliminates the loss of a part of information about the signal (more than half) in comparison with a well-known device, its effectiveness

0 applications in terms of noise immunity will be within 3 dB.

Claims (1)

Invention Formula A device for demodulating frequency-modulated signals at a low carrier-to-modulation frequency ratio, comprising a series-connected band-pass filter, an amplifier-limiter, a signal edge separation unit, a first counter, a first envelope selection unit, a control unit, and a controlled oscillator, whose output connected to the first input of the signal generator, the second input and the output of which are connected respectively to the output of the frequency divider and the first input of the coincidence block, to the second input of which you are connected the stroke of the first counter, the second input of which is connected to the second input of the controlled oscillator, the input of the frequency divider, the output of the high-frequency generator and the first input the second counter, the outputs of which are connected respectively to the third input of the first counter and to the first input of the crushing block, the output of which is connected to the second input of the edge separator, the output of which is connected to the second inputs of the second counter and the crushing block; and the output of the coincidence block connected to the second input of the control unit, so that, in order to improve the noise immunity, the third counter, the And / two triggers, the OR elements and the second envelope highlighting block, Which odes are connected to the first inputs of the corresponding elements. And, the second inputs and outputs of which are connected appropriately with the first output of the third counter and the first inputs of the OR elements, the second inputs of which are connected to the second and third outputs of the third counter, while the outputs of the OR elements are connected to the inputs of the first trigger, the outputs of which are connected to the first inputs of the corresponding elements And, the second inputs of which are connected to the additional output of the controlled generator and the first input of the third counter, the second input of which is coeqni with the output of the signal edge selection unit and the first input the house of the second block of the selection envelope, to the second input of which an additional output of the first counter is connected, and the outputs of the corresponding elements And are connected to the inputs of the second trigger. Sources of information taken into account in the examination 1. USSR author's certificate 441680, cl. H 04 L 27/24, 1972. /9 / S 21