JPS62150507A - Reproducing equalizer - Google Patents

Abstract

PURPOSE:To improve the S/N while preventing the occurrence of an inversion by supplying a reproduced high frequency signal to an addition/subtraction circuit additively via a delay circuit and supplying the signal to the addition/ subtraction circuit subtractingly via a nonlinear circuit. CONSTITUTION:An output of an equalizer 2 is supplied to an addition/ subtraction circuit 11 of a reproducing equalizer 10 via a main transmission line 5, a delay circuit 6 and a variable resistor 7 additively and supplied subtractingly via the 3rd transmission line comprising a limiter 12 as a nonlinear circuit, the 2nd variable resistor 13 and a low pass filter 14 and an output of the reproducing equalizer 10 is fed to a demodulator via a limiter 8. The threshold level of the limiter 12 is set higher than the level of an FM-RF signal when the modulation factor is large, a low side band SL in the FM-RF signal passing through the limiter 12 and the variable resistor 13 is fed to the addition/ subtraction circuit 11 via the low pass filter 14, the intensity of the low side band SL is suppressed to prevent the occurrence of the inversion. Thus, the S/N is improved further while preventing inversion.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a playback equalizer for a video tape recorder.

[Summary of the invention]

The present invention combines a directly supplied reproduced RF signal and a reproduced RF signal passed through a delay circuit with 3E1. By providing linear phase characteristics and slope amplitude characteristics, and subtracting the reproduced RF signal that has passed through the non-linear circuit, the degree of emphasis of the lower sideband of the reproduced RF signal is adjusted according to the modulation index of the high frequency modulation signal. In order to further improve the performance while preventing the single reversal phenomenon, we have achieved six results.

[Conventional technology]

Conventionally, video tape recorders (hereinafter abbreviated as VTR)
The reproducing system was constructed as shown in FIG. 3, for example.

In FIG. 3, (1) is a reproducing magnetic head that is representative of a plurality of rotating magnetic heads, and the output of the reproducing magnetic head (i.e., a frequency-modulated high-frequency signal (FM
- The RF multiplied signal is supplied to a regenerative equalizer (3) via a regenerative amplifier (not shown) and an equalizer (2).

The output of the equalizer (2) is directly supplied to the adder circuit (4) of this Ao equalizer (3) via the main transmission path (5), and a delay circuit (6) with a delay time τ is also supplied. ) and a variable resistor (7), the phase characteristic is made linear, and the amplitude characteristic is made into a high-frequency suppressing type with a linear slope. The output of the reproduction equalizer (3) is connected to the limiter (8
), and the output of the limiter (8) is supplied to a demodulation circuit (not shown), where it is demodulated into a video signal.

In the above-mentioned VTR playback system, the lower sideband is emphasized and the upper sideband is suppressed in the reproduced FM-RF fA signal from the readback magnetic head (1) due to the nonlinearity of the tape head system. Therefore, the S of the upper sideband wave is higher than that of the lower sideband wave.
/N is getting worse. Moreover, there is almost no phase difference between them.

By the way, when a video signal rises sharply from the black level to the white level, an overshoot occurs due to pre-emphasis at this rising part, and the instantaneous frequency of the FM-RF flaw signal corresponding to this part is becomes very expensive.

When this FM-RF flaw signal passes through a transmission system including the tape head system as described above.

The amplitude of the spike-corresponding part becomes smaller and falls outside the slice range of the limiter in the front stage of the demodulator, resulting in a loss of output from the limiter. This loss is equivalent to a lower frequency of the FM-RF signal input to the demodulator. The OI modulator output becomes a black level signal.

When this reversal phenomenon occurs, the RF signal waveform lacks the zero-crossing point in the spike-corresponding part. Also, the FM at this time
-RF flaw signal, as shown in the instantaneous vector diagram in Figure 4,
Compared to carrier C and upper sideband SU.

If the amplitude of the lower sideband wave SL is large and the phase difference between the lower sideband wave SL and the carrier wave C (and the upper sideband SU) is close to 180°, the fcRF signal will have a negative amplitude by combining the three. will have.

As a countermeasure against the above-mentioned inversion phenomenon, in the conventional VTR playback system, the equalizer (2) equalizes the levels of the upper and lower sidebands SU and SL, and then the playback equalizer (3) adjusts the S/N. Suppresses bad upper sideband waves S and J (lower sideband S
(emphasizes L) and then demodulates.

The inversion phenomenon was prevented without deteriorating the overall S/N.

[Problem that the invention seeks to solve]

However, as is well known, the FM-RF flaw signal of a VTR is a carrier wave C and both side band waves S. and the amplitude of SL is m′
! ! :0th and 1st order Bessel functions J0(rr+) and J, (m) and J-1 as modulation indices, respectively
(m).

And like the above-mentioned part of the video signal.

When the level of the high-frequency modulation signal is large, the modulation index becomes sharper, the amplitudes of both sideband waves SU and SL increase, and the amplitude of the carrier wave C decreases.

For this reason, in the conventional lower sideband emphasizing type regenerative equalizer, as the modulation index by the high frequency modulation signal increases, the amplitudes of the carrier wave and both sidebands of the output will have a relative relationship as shown in Figure 4. , the reversal phenomenon becomes more likely to occur. Therefore, in the conventional regenerative equalizer, there is a problem in that the degree of emphasis of the lower sideband is limited, and accordingly, the degree of S/N improvement is also limited.

In view of this, an object of the present invention is to provide a regenerative equalizer that further improves the S/N ratio while preventing the occurrence of the inversion phenomenon2).

[Means for solving problems]

The present invention includes an addition/subtraction circuit to which a reproduced high-frequency signal is supplied to the DW terminal, a delay circuit, and a nonlinear circuit.

This is a regenerative equalizer in which a reproduced high-frequency signal is additively supplied to an adder/subtractor circuit via a delay circuit, and a reproduced high-frequency signal is subtractively supplied to an adder/subtracter circuit via a non-linear circuit.

[Effect]

According to this configuration, the degree of emphasis of the lower sideband changes according to the modulation index of the reproduced high-frequency signal by the high-frequency modulation signal, preventing the inversion phenomenon and further improving the S/N.

[Embodiment] An embodiment of the regenerative equalizer according to the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, parts corresponding to those in FIG. 3 are designated by the same reference numerals and redundant explanation will be omitted.

In Fig. 1, the output of the equalizer (2) is added to the addition/subtraction circuit α◇ of the regenerative equalizer αQ via the main transmission path (5), delay circuit (6), and variable resistor (7). limiter (6) as a non-linear circuit.
, a second variable resistor (to) and a low-pass filter α→.

The output of this regenerative equalizer αQ is passed through a limiter (8).

The signal is supplied to a demodulator (not shown).

Note that it is preferable that the cutoff characteristic of the low-pass filter 04 has a gentle slope that is point symmetrical about the FM-RF multiplied signal carrier frequency.

Next, the operation of this embodiment will be explained with reference to FIG.

For small amplitude reproduced FM-RF multiplied signal, variable resistor (7)
Letting the transmission coefficients of and (to) be α7 and α13, the amplitude characteristic A ((b) of the reproduced equalizer signal is expressed as the following equation (1).

In this embodiment, the target Ji'M-RF signal amplitude becomes small when the modulation index m by the high-frequency modulation signal is large, and the amplitude of the Ji'M-RF multiplied signal becomes small as described above. In FM-RF No. 9, as shown in FIG. 2A, the amplitudes of both sideband waves SU and SL are large, and the amplitude of the carrier wave C is small, so that there is little margin for occurrence of an inversion phenomenon. Therefore, in this embodiment, the threshold level of the limiter (2) is set to FM-RF when the modulation index is large.
P is also set higher than the double signal level, and the middle lower sideband wave SL of the fCFM-RF flaw signal passes through the limiter (2) and variable resistor α3, and is supplied to the adder/subtractor circuit α through the low-pass filter α rod, and then According to equation (1), the degree of emphasis of the lower sideband wave SL is suppressed and the occurrence of the 1-inversion phenomenon is prevented.

Conversely, the FM-RF multiplied signal amplitude becomes large when the modulation index by the high frequency modulation signal is small.

In the signal on the input side of the regenerative equalizer αQ, as shown by the solid line in FIG. 2B, the amplitudes of both carrier waves SU and SL are small.

Since the amplitude of the carrier wave C becomes large, there is a large margin for occurrence of an inversion phenomenon.

The threshold level of the limiter (6) as described above is lower than the FM-RF multiplied signal level in this case. , ) is supplied to the lower sideband SL
The relative value of decreases. This is α, which is Q to equation (1) above.
If the F'M-RF multiplied signal level exceeds the threshold level of the limiter (6), as shown by the broken line in Figure 2B, there is a margin for the occurrence of the inversion phenomenon. It is possible to emphasize the 'F sideband waves Sl and li while maintaining the same, and it is possible to further improve the tide.

In the above description, the limiter (6) is used to control the characteristics of the regenerative equalizer (10), but a non-linear circuit such as a compression circuit or a logarithmic amplification circuit may also be used.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to control the degree of emphasis of the lower sideband of the reproduced U signal according to the modulation index of the high frequency modulation signal, and to prevent the inversion phenomenon while /
A regenerative equalizer that can further improve N is obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a regenerative equalizer according to the present invention, FIG. 2 is a vector diagram for explaining the operation of the embodiment of FIG. FIG. 4 is a block diagram showing an example of the configuration of the equalizer, and is a vector diagram for explaining the present invention. (3) and αQ are regenerative equalizers, (6 is a delay circuit, αη
is an addition/subtraction circuit, and (6) is an lJ mitter (nonlinear circuit).

Claims (1)

[Claims] An adder/subtractor circuit to which a reproduced high-frequency signal is directly supplied, a delay circuit, and a non-linear circuit, wherein the reproduced high-frequency signal is additively supplied to the adder/subtracter circuit via the delay circuit. and the reproduced high-frequency signal is subtractively supplied to the addition/subtraction circuit via the non-linear circuit.