SU736164A1 - Device for reproducing signals from magnetic carrier - Google Patents

Description

The invention relates to instrumentation and can be used in magnetic recording and reproducing equipment of frequency modulated (FM) signals. A device is known in which, during demodulation of FM signals, the carrier frequency is multiplied, which reduces the combinational noise, increases the reliability of the reproduced signal 1. However, in a number of cases the interference suppression in these devices is insufficient, since only carrier quadrupling. A device for reproducing signals from a magnetic carrier, in which the carrier frequency is multiplied by 8 2, is known. This device contains serially connected magnetic head, amplifier and band-pass filter. A differentiating circuit is connected to the output of the band-pass filter. One circuit is connected to the output of the differentiating circuit; the state of the series-connected first amplitude limiter, the first low-pass filter and the first shaper connected by its two outputs to the first and second inputs of the main one, respectively; ; 1 h) pa, connected to its output through the radio., A multivibrator with a terminal filter of the lower frequencies. A second circuit is connected to the input of the differentiating circuit; the second amplitude limiter, the second low-pass filter and the second driver, which is connected to the third and fourth inputs of the main adder, are connected in series. In addition, this device contains an additional adder, the first input of which is connected to the output of the first low-pass filter, the second input to the output of the second low-pass filter, and the output through the third driver to the fifth and second inputs of the main adder, and the subtraction unit connected the first input to the output of the first low-pass filter, the second input to the output of the second low-pass filter, and the output through the fourth driver to the seventh and eighth input and the main adder. In this device, the differentiation circuit performs the function of a signal phase shift unit by 90 °, without which further frequency multiplication of more than 2 is impossible. However, it is not possible to accurately differentiate the signal in a wide frequency range, which reduces the effect of multiplying the carrier frequency by 8 and consequently, the accuracy of reproduction of information in this device.

The aim of the invention is to improve the accuracy of reproduction recorded on magnetic media.

For this purpose, in the proposed device, the differentiating circuit is replaced with a phase shift block containing a delay line and into the cascade cascade included in the first of these circuits and a summing cascade included in the second circuit, the outputs of these cascades are connected respectively to the inputs of the first and the second amplitude limiters, and interconnected first inputs directly, and the second inputs through the delay line to the output of the bandpass filter.

FIG. 1 shows a block diagram of the proposed device; in fig. 2 - diagrams explaining the principle of its work.

The input part of the device is a reproducing magnetic head 1, to the output of which amplifier 2 with a band-pass filter 3 is connected. To the output of the band-pass filter there is an input of a phase shift unit 4 consisting of a delay line 5, a subtracting stage 6 and a summing stage 7. Moreover The input consists of the input of the delay line 5 and the first inputs of the subtracting stage 6 and the summing stage 7 connected. E the second inputs of the subtracting 6 and the summing 7 stages are connected to the output of the delay line. A first signal processing circuit is connected to the output of the subtracting stage 6, which consists of the first amplitude limiter 8, the first low-pass filter 9 and the first generator 10 connected in series. A second signal processing circuit containing the second amplitude limiter 11 connected in series to the output of the summing stage 7 the second low-pass filter 12 and the second driver 13. To the output of the first low-pass filter 9 are connected the first inputs of the additional adder 14 connected to the three A shaper 15 and a subtractor 16 connected to the fourth shaper 17. To the output of the second low pass filter 12 are connected the second inputs of the additional adder 14 and the subtractor 16. The first 10, second 13, third 15 and fourth 17 shapers have two outputs each. Moreover, each output is connected to its input of the main adder 18, which is connected to the low-pass termination filter 20 through a waiting multivibrator 19.

The device works as follows.

Frequency modulated signal

(see fig. 2a) reproduced by magnetic

head 1 and amplified by amplifier 2, through a band-pass filter 3, limiting the band noise, enters the phase shift unit 4 simultaneously to the input of the delay line 5 and the first inputs of the subtractive 6 and summing 7 stages. This signal is shown. At the second inputs of the subtracting and summing stages, a delayed signal is received (see Fig. 25) from the output of the delay line 5. The output signal of the subtractive stage 6 (see Fig. 20) has a phase shift of 135 °,

0 and the output signal of the summing stage 7 (see Fig. 9l) is a phase shift of 45 ° with respect to the output signal of the delay line 5 (see Fig. 25), i.e. among themselves they have a phase shift of 90 °.

From the output of the subtracting stage 6, the signal enters the first processing circuit, where it is first limited by the first amplitude limiter 8, which eliminates the possible parasitic amplitude modulation and gives the signal a rectangular shape

0 (see Fig. 29), and then applied to the first low-pass filter 9. After passing through the first low-pass filter, the signal again becomes smooth (see Fig. 2g). Next, the signal arrives at the first driver 10. At one of its outputs

 and there is a sequence of negative pointed pulses (see Fig. 2g), which are produced at times of zero values of the input signal of the driver when it decreases. At the second output there is a sequence of positive pulses (see Fig. 2h), which are also produced at the moments of zero values of the input signal, but already as it increases.

The output of summing stage 7 (see Fig. 2) enters the second circuit, where it is also first subjected to limitation using the second amplitude limiter 11 (see Fig. 2it), then passes the second low-pass filter 12, acquiring a smooth shape (see Fig. 2k) and is converted by the second driver 13 into two opposite polarity sequences of pointed pulses (see Fig. 2n, -m).

The filters 9 and 12 of the lower frequencies (see Fig. 2e, k) are also fed to different inputs of the additional adder 14 and to different inputs of the subtractor 16. At the output of the additional adder 14, a signal is out of phase with respect to the signal (see Fig 2e) at 45 ° (see fig. 2n). From it, using the third driver 15, two pulse sequences are formed (see Fig. 2o, a).

At the output of the subtraction unit 16, a signal is received that is ahead of the signal in the phase (see Fig. 2e) by 45 ° (see Fig. 2p). From this

5 signals using the fourth driver 17, two more pulse sequences are formed (see fng. 2c, w).

From the outputs of all four drivers, eight pulse sequences are passed to eight inputs of the main adder 18. Moreover, negative pulses are fed to the inverting inputs of the adder, and positive ones to the non-inverting ones.

At the output of the main adder 18 there is a sequence of unipolar pointed pulses (see Fig. 2y) of the measured frequency, which triggers the waiting multivibrator 19. The output of the waiting multivibrator receives rectangular pulses of constant duration (see Fig. 2f).

Using a low pass filter 20, a modulating signal {see. FIG. 2x).

The invention improves the accuracy of information reproduction.

Claims (2)

1. USSR author's certificate number 460566, cl. G 11 B 5/02, 1974. 2. USSR author's certificate 0 No. 568069, class G 11 5/04, 1976 (prototype). n  f to to to to to to to to to to to to to p p p p p p p p p p p p p p p p I X