SU1688444A1 - Coherent demodulator of phase-manipulated signals - Google Patents

Abstract

The invention relates to radio engineering and can be used when receiving phase-shift (FM) signals. The purpose of the invention is to improve noise immunity. A coherent demodulator contains phase detectors 1, 2, phase shifters 4, 5, low pass filter 7, synchronous local oscillator 11, multiplier 12, comparator 13, switch 14. The goal is achieved by introducing a phase detector (PD), phase shifter 6. filters 8-10 lower frequencies, switches 15, 16 The demodulator eliminates the error angle (f, If the output of the comparator is 13Vynp 1/2, then the PD 3 will receive a reference signal from the output of the phase shifter 5 through the first input of the switch 15 In this case, 3i / 4 - ((- / 4) 0. If the output of the comparator 13 is Vynp -1/2, then at the first input of the PD 3 by The reference signal comes from the output of the phase shifter 5 through the second input of the switch 15. From the output of the PD 3, the signal goes through the filter 10 and the first input of the switch 16 to the first output of the demodulator.In both cases, the demodulator circuit is converted to an optimal coherent demodulator circuit for receiving single FM signals. 1 or.

Description

The invention relates to radio engineering and can be used when receiving phase-shift (FM) signals.

The purpose of the invention is to improve noise immunity.

The drawing shows a structural diagram of the proposed coherent demodulator.

Coherent demodulator contains first, second, third phase detectors 1-3, first, second, third phasers 4-6, first, second, third, fourth low-pass filters 7-10, synchronous local oscillator 11, multiplier 12, comparator 13, first , second, third switches 14-16.

The coherent demodulator works as follows.

Let a double FM signal (a four phase FM signal) be received at the input of the demodulator. In this case, the transmission can be carried out simultaneously from two sources using two orthogonal FM signals or from one source by the method of quadrature (double) phase manipulation. In both cases, different binary sequences will form at the outputs of filters 8 and 9. The voltage at the output of the multiplier 12 is a binary sequence with a zero average value, which is extracted by the filter 7 and is fed to the input of the comparator 13. In accordance with the logic of the comparator 13, it is formed at its output, which goes to the control inputs of the switches 16.14 . Latest OS 00

with

There are switching outputs of filters 8 and 9, respectively, with the first and second outputs of the demodulator. Thus, the scheme of the proposed demodulator will be transformed into an optimal coherent demodulator circuit for receiving double FM signals. In this mode, the principle of operation of the proposed device does not differ from the operation of the prototype.

Suppose now that a single (two-phase) FM signal arrives at the input of the demodulator, the analytical expression of which can be written as

So (t) -A0 cos (oio t + p (t) pp, (1)) where DO is the carrier frequency, is equal to the frequency of the synchronous local oscillator 11;

y (t) is the phase function containing the transmitted information sequence;

fPv The mismatch angle between the carrier and reference signal of the synchronous local oscillator.

Mr L

If T . then the phase manipulation on

O or l occurs between two absolute, l 3 L-. The values of {-g; - -g-. At the same time

The outputs of the filters 8 are separated by two identical binary sequences, the amplitude of which is 2 times less than in the case of receiving a single FM signal by an optimal receiver of single FM signals.

If /) p - -d, then the phase manipulation on O or l occurs between two absolute values.

}

the phase values {+ -jr-,

At the same time, at the outputs of the filters 8 and 9, two oppositely opposite sequences are distinguished, the amplitude of which is also smaller than in the case of receiving a single FM signal by an optimal receiver of single FM signals.

At the same time, if r, when transmitting the symbol +1 at the output of the multiplier 12, the positive voltage

(since - -), and when transmitting

-1 characters also according to Wits positive, -1-11 l

voltage (as - - - -).

Thus, at the output of the filter 7, a constant positive voltage will be formed (which is a sign that the received FM signal is a single signal

and ft)

GL

If (. When transmitting the character

+1 at the output of the multiplier 12 in vits negative voltage (since

1-11,

  v / 5 j) and transmitting the symbol

-1 Wits negative voltage (as t /). In this way,

a permanent negative voltage will be generated at the output of the filter (which is a sign that the received

FM signal once and)

Unlike the prototype, in the proposed device, after determining the multiplicity of manipulation (double or single) and the angle for single

FM signals (-g or--) occur

elimination of mismatch angle tfy).

However, if the comparator output

13 Vynp V, then at the first phase input

the detector 3 receives the reference signal from the output of the phase shifter and through the first input of the switch 15. The resulting will be equal to

ft- + (-) o.

If the output of the comparator 13 is, then at the first input of the phase

the detector 3 will receive the reference signal from the output of the phase shifter 5 through the second input of the switch 15. In this case, the resulting pp will also be equal to

. l f l A 4 + 2 + (4) °

From the output of the phase detector 3, the signal through the filter and the first input of the switch 16 is fed to the first output of the demodulator. In both cases and, therefore, the proposed demodulator circuit is transformed into an optimal coherent demodulator circuit for receiving single FM signals.

Claims (1)

Claims of invention a phase shifter with a second input of a second phase detector, a serially connected multiplier, a first low-pass filter, a comparator, The first switch, the output of which is the second output of a coherent demodulator, is characterized in that, in order to improve noise immunity, a second, third low-pass filters, a second switch connected in series, a third phase shifter, a third phase detector, a fourth low-pass filter, and the third switch, the output of the first phase detector through the second low-pass filter connected to the first input of the multiplier, the output of the second phase detector through the third low-pass filter connected to torym 0 input multiplier, the output of the first f - amplifier is connected to the first input of the second switch, the second and third inputs of which are connected respectively to the output of the second phase shifter and the comparator output connected to the second input of the third switch, the third input of which is connected to the output of the second low-pass filter, and the output is the first output of a coherent demodulator, the output of the third low-pass filter is connected to the second input of the first switch, the second input of the third phase detector is the coherent input ntnogo demodulator.