SU1737737A1 - Device for conversion of frequency-modulated analog signal into digital one - Google Patents

Abstract

The essential feature of the present invention lies in the fact that with the aid of strictly digital methods, the frequency-modulated analog signal is converted directly into a digital code N proportional to the deviation f of the signal of intermediate frequency f. The device includes a converter 1, a comparator 3, a frequency divider 5, a unit 6 for measuring the duration of the pulses, a processor 7, a signal separation unit 8 and a synchronisation pulse generator 9. The invention finds a preferred application for frequency-modulation radio signal receivers. <IMAGE>

Description

A device for converting a frequency-modulated analog signal to a digital signal contains a converter 1 of a frequency-modulated analog signal into an intermediate frequency signal, a comparator 2, a frequency divider 3, a measuring unit 4 of pulse duration, a calculator 5 of the intermediate frequency deviation code, and a driver 6 of control pulses frequency generator 7, a filter 8, a comparator 9, shapers 10, 11 short pulses and an OR 12 element, are included in the driver 6, and the converter 1 is converted into the converter 1 Recipient of frequency 13 and two half-period rectifier 14.

A device for converting a frequency-modulated analog signal to a digital signal operates as follows.

In converter 1, the frequency modulated signal is converted to an intermediate frequency signal with doubled frequency deviation

Af 2 Af, where Af If-fol.

f is the frequency of the signal at the output of the converter 1.

fo is the unmodulated frequency value.

This signal is fed to the first input of the comparator 2, the second input of which receives the reference voltage, which in the particular case may be zero. At the output of comparator 2, a sequence of rectangular pulses is formed with frequency parameters adequate to the parameters of the input signal f (Fig. 4, a). Frequency divider 3, measuring unit 4 and calculator 5 are reset to the initial state by a strobe formed by shaper 6 with a period Td (Fig. 4, c).

The signal from the output of comparator 2 (Fig. 4, a) is fed to the frequency divider 3, in which the division is performed K times, where

at

K „9, Td - sampling period,

tM3KC -

1max 1

- the maximum period of time Affo Af f.

At the output of frequency divider 3, a time interval is formed, the duration of which is proportional to the instantaneous value of the intermediate frequency period (Fig. 4.6). This time interval is measured in a pulse width measurement unit 4. In particular, the measurement can be carried out by counting the pulses of the reference frequency of the local oscillator

during the interval. At the end of the measurement, at the output of measurement unit 4, the code of the interval NT is generated, which is fed to the input of the calculator 5, which implements the transformation in each successive cycle (during the sampling period)

| ANF | L Nf IAINJFI Nj to,

where k is the frequency division factor of 3;

0 Nf0 is the code of the unmodulated value of the intermediate frequency fo,

NT is the duration of the measured interval,

| ANp I-intermediate intermediate

5 frequencies.

When performing calculator 5 in the form of a serially connected multiplier and combinational adder operating in subtractor mode) to the input of a multiplier that performs operation 1 / Ni,

0 enters NT code. At its output, in accordance with its functional purpose, an I / NT code of the instantaneous intermediate frequency value is generated over the sampling period. Then from this code using

5, the subtractor subtracts the constant Nf0 - the code of the unmodulated frequency value F0,

equal to-tA The Nfo code can be formed using a set of constant voltage sources, the levels of which correspond to the levels of logical zeros and ones distributed and connected to the subtractor inputs in the order corresponding to the value of the Nfo code. In this way,

5, at the output of the subtractor 5, for each sampling period, a code | D NF is generated to de-eziatsii intermediate frequency Af.

In the next cycle, the processes of dividing the frequency, measuring the duration of the pulses and calculating lANpl are repeated, starting with the appearance of the strobe n (Fig. 4c). The duration of the Tob processing interval (Fig. 4, d, e), during which one process of the described transformations occurs, is chosen from the conditions

KtMaKC Tob Td.

The operation of shaper 6 is as follows. At its input receives a signal from the output of the comparator 2 (Fig. 5, a). After processing it with a frequency detector 7, the signal separating the subcarrier and the filter 8 separating the subcarrier, the signal 1) φ (Fig. 5.6) is fed to the comparator 9, which distinguishes the positive and negative half-waves of the subcarrier. The signals from the direct and inverse outputs of the comparator 9 (Fig. 5, c, d) through shapers 10, 11 short pulses and the element OR 12 and 0

five

step on the output of the imager 6 (Fig. 5, d). The pulse duration at the output of the former 6 is TCT. The minimum duration of their duration is determined by the required duration of setting the frequency divider 3, measuring unit 4 and calculator 5 to the initial state. For each strobe pulse r0, PI, etc. The next cycle of the device operation begins.

The device in each cycle (sampling period) determines the code equivalent of the difference in frequency A f from its unmodulated value f0 during the sampling period, with each measurement cycle being performed in half-intervals of the subcarrier frequency located in the zone of its extremes.

Claims (1)

Formula of Invention A device for converting a frequency-modulated analog signal to a digital signal, comprising a converter of a frequency-modulated analog signal into an intermediate signal. 0 five 0 five frequency and calculator, characterized in that, in order to increase the accuracy of converting a frequency-modulated analog signal into a digital signal, the calculator is designed as a calculator of the intermediate frequency deviation code and a control pulse driver and serially connected comparator, frequency divider and pulse duration measuring unit are inserted , while the output of the frequency modulated analog signal converter to the intermediate frequency signal is connected to the first input of the comparator, the second input which is the reference voltage input, and the comparator output is connected to the input of the control pulse generator, the output of which is connected to the control inputs of the frequency divider, the pulse duration measuring unit and the intermediate frequency deviation code calculator, to the signal inputs of which the corresponding outputs of the duration measuring unit are connected pulses. whh one 1 db CO a Fig 5