SU1376254A1 - Demodulator of frequency-modulated stereo signal in polar modulation system - Google Patents

Abstract

The invention can be used in high-quality stereo broadcast reception equipment and provides an increase in the accuracy of signal demodulation. The demodulator contains analog switches (AK) 1, 2, a correction unit 3, a subcarrier frequency separation unit 4, an intermediate frequency pulse shaper 5, and a reference voltage source 6. Shaper 5 converts the input frequency-modulated stereo signal with polar modulation into a pulse train with a normalized amplitude and duration. Unit 4 of this sequence, which is a pulse-frequency modulated signal, extracts the subcarrier frequency and the antiphase subcarrier frequency. These signals come in acc. AK 1, 2, which also receives a constant voltage source 6. AK 1, 2 are controlled by frequency-pulse-modulated signals. As a result of the switching, either a subcarrier is shifted from the above-tone to the tonal part, or a total signal is generated. In this case, the signals of the left and right channels are formed. 3 ep f-ly, 6 ill. with (L

Description

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The invention relates to radio engineering and communications and can be used in high-quality equipment for receiving stereo broadcast signals. .

The aim of the invention is to improve the accuracy of signal demodulation.

Figure 1 shows a structural electrical circuit of a demodulator of a frequency-frequency modulated (FM) stereo signal in a polar modulated system; Fig. 2 shows the same; alternatively; Fig. 3-5 shows structural circuit diagrams of embodiments of the first and second analog switches; 6 shows signal spectra in demodulator cross sections.

The FM stereo demodulator in the polar modulation system contains the first 1 and second 2 analog switches, the correction unit 3, the subcarrier frequency allocation unit 4, the intermediate frequency pulse shaper 5, and the adjustable reference voltage source 6. The first 1 and second 2 analog switches contain the first adder. 7, the first 8 and the second 9 analog keys, and the second key 3.

The FM stereo demodulator in a polar modulation system operates as follows.

Shaper 5 converts the polar-modulated input-FM stereo signal (the spectrum of this signal is shown in Fig. 6b), which is fed to the input of the demodulator from the output of the FM receiver's intermediate frequency amplifier, into a sequence of pulses with normalized amplitude and duration. This pulse train is a frequency-pulse modulated (PFM) signal, the spectrum of which, in addition to the components around the intermediate frequency and its harmonics, contains the low-frequency spectrum of the frequency-demodulated stereo signal (Fig.66). Block 4 extracts from the PFM signal the subcarrier frequency (Fig. Bb) and the antiphase subcarrier frequency (Fig. Bg). These signals are respectively fed to the signal inputs of the first 1 and second 2 analog switches. Their second signal inputs are supplied from a source 6 with a constant voltage (FIG. D). Since the control inputs of the first 1 and second 2 analog switches

the PFM signal arrives (Fig.66), then with the result of switching the subcarrier-frequency, selected by block 4, the overtonal part shifts to tonal, as a result of switching the source 6 of the reference voltage, the total signal passes, and at the outputs of the first 1 and second 2 Left and right (A and B) channel signals appear on the go-on switches (fig.be, u, g).

In the low-frequency region, the difference signal (А-В) on the transmitting side is partially suppressed. Unit 3 will correct in the channels A and B the antiphase (difference) low-frequency part of the spectrum due to its differential switching. Weekends

0, signals 3 are signals A and B (FIG. 8).

The first 1 and second 2 analog switches can be one two-input adder 7 and an analog key 8 (FIG. 3). This scheme

corresponds to the two-quadrant mind-. The pulse modulator, i.e. oscillations with a subcarrier frequency pass to the output of the first 1 and second 2 analog switches. By using four inputs of the first 1 and the second 2 analog switches (Fig. 2), this component can be eliminated. In the latter case, the first 1 and second 2 analog switches correspond to four-quadrant multipliers with pulse modulation (Figures 4 and 5). The first circuit (figure 4) consists of the first and second analog switches 8 and 9 and the two-input adder 7, the second circuit (fig. 3) - from the first 7 and second 10 adders and the first analog key 8. Using a four-quadrant multiplier Pulse modulation source 6 must have a second additional output. I

To suppress high frequency

Q components of the signal at the output of the device with frequencies of the intermediate frequency and above it is advisable to use low-pass filters.

Claims (6)

1. A frequency modulated stereo demodulator in a polar modulated system, comprising five 0 five the first and second analog switches, the outputs of which are connected respectively to the first and second inputs of the correction unit, as well as the drive frequency separation unit, the first and second outputs of which are connected to the first inputs of the first and second analog switches, the second inputs of which are combined, differing in that, in order to improve the accuracy of signal demodulation, an intermediate frequency pulse shaper and a reference voltage source, the output of which is connected to the second input of the first analog switch, the third input of which is combined with the third input of the second analog switch and the input of the subcarrier frequency block and is connected to the output of the intermediate frequency pulse generator, 2. The demodulator of claim 1, wherein the first and second analog switches each comprise a series-connected adder and an analog switch, the output of which is the output of the analog switch, the first and second inputs of which are respectively the first and the second inputs of the adder, and the control input of the analog switch is the third input of the analog switch. 3. A demodulator as claimed in claim 1, wherein the voltage source is made adjustable. 4. A demodulator according to claim 1, wherein the voltage source has a second output connected to the combined fourth inputs of the first and. second analog switches, the combined fifth inputs of which are connected to the second output of the subcarrier frequency control unit. 5. Demodulator according to claim 4, characterized in that the first and . Jq 20 25 l 35 40 45 The second analog switches contain each first and second analog switches, the outputs of which are connected to the corresponding first and second inputs of the adder, the output of which is the output of the first and second analog KONMyTaToders, respectively, the first input of each of which is the first input of the first analog key, the second input of which is the second input of the first analog switch and the fourth input of the second analog switch, the third inputs of the first and second analog switches are connected nennye control inputs of the first and second analog switches, a first input of the last of which is the fourth input of the first analog switch and a second input of the second analog switch, a second input of the second analog switch is tymi n inputs of said first and second analog switches. 6. The demodulator of claim 4, wherein the first and second analog switches each contain first and second adders, the outputs of which are connected respectively to the first and second inputs of the analog switch, the output of which is the output of the corresponding switch the first and second analog switches, the first input of each of which is the first input of the first adder, the second input of which is the second input of the first analog switch and the fourth input of the second analog switch, the control input analog The first key is the third input of the first and second analog keys, the first input of the second adder is the fourth input of the first analog switch and the second input of the second analog switch, the fifth input of each of which is the second input of the second adder. FIG. 2 FIG. Fy W but FIG. 5, P ilniH П1пГПП | П П | ПГПП | Л / t nt 2fn4 w ha uLE R  L LI 2fn4