JPH04183081A - Picture reproducing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to an image reproducing device such as a video tape recorder (VTR) using a low carrier FM recording system □.

[Prior Art] For example, in a VTR that performs low carrier wave FM recording, waveform equalization is performed on the reproduced FM signal in order to compensate for loss in the magnetic recording system.

In particular, in professional VTRs, the video signal band is wide and the deviation is set wide in order to obtain a high S/N ratio, and recording and playback of FM signals with this wide deviation is realized by highly accurate waveform equalization. .

[Problems to be Solved by the Invention] However, in the conventional example described above, there is a drawback that when the recording and reproducing characteristics change due to changes over time, the residual equalization error increases and the image quality deteriorates.

In particular, changes in recording and reproducing characteristics due to wear of the magnetic head cause significant deterioration in image quality.

An object of the present invention is to provide an image reproducing device that solves the above-mentioned problems.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a reproducing means for reproducing a low carrier FM recording signal recorded on a recording medium, and a reproducing means for equalizing the waveform of the reproduced FM signal from the reproducing means. an equalizer, and a detection means for detecting an envelope of a portion of the signal from the reproduction equalizer in which the level of the modulated signal changes;
The apparatus is characterized by comprising means for controlling the reproduction equalizer based on the detection result of the detection means.

[Function 1] According to the present invention, a video level signal whose level changes continuously or stepwise is reproduced from a recording medium, and an equalizer is controlled based on the envelope value of the reproduced FM signal. This prevents deterioration in the quality of reproduced images due to changes over time.

〔Example] The following will be explained based on examples.

FIG. 1 is a block diagram showing an embodiment of the present invention.

The input modulated signal is FM modulated by an FM modulator 1, amplified by a recording amplifier 2, and written (recorded) on a magnetic tape 5 by a magnetic head 4 via a rotary transformer 3. Table 1 shows carrier wave frequencies in the FM modulator 1.

Table 1 Considering FM modulation where the modulated signal band is 12 MHz and the maximum deviation after emphasis is about 20 MHz,
The FM signal band is approximately 7 to 31 MHz.

During playback, the signals recorded on the magnetic tape 5 are read out (played back) by the magnetic head 6, passed through the rotary transformer 7, amplified by the playback amplifier 8, and then output to the FQ.
A frequency correction circuit (frequency correction circuit) 9 corrects the frequency characteristics of the reproduction system. In the FQ converter 9, the magnetic head 6, rotary transformer 7, reproducing amplifier 8, etc. create a resonant characteristic opposite to that of the reproducing circuit, so the output signal of the FQ converter 9 is different from the output of the FM modulator 1. , it becomes a signal that has suffered only the loss in the magnetic recording system. The output of the FQ compensator 9 is processed by an equalizer 10 to compensate for losses in the magnetic recording system.
The signal is demodulated by the FM demodulator 12 and output.

Here, information corresponding to equalization error fluctuation is obtained from the output of the equalizer 10, and the equalizer controller 11 controls the equalizer lO,
Perform automatic equalization.

As shown in FIG. 2, the equalizer lθ includes a 10 equalizer 13,
It consists of three types of equalizers: a cosine equalizer 14 and a sideband suppression equalizer 15.

In this embodiment, the equalizer 13 uses an LC filter to create highly accurate inverse characteristics of the frequency characteristics of the magnetic recording system obtained from recording and reproduction of a single frequency signal, and compensates for losses in the magnetic recording system. , a rectangular wave is used as the recording waveform of the FM signal, and the magnetic recording system can be compensated by the 10 equalizer 13 even under the wide deviation conditions mentioned above. 1
The frequency characteristics of the zero equalizer 13 are shown in FIG. 3. The solid line in FIG. 9 is the equalizer characteristic, and the broken line is the inverse characteristic of the frequency characteristic of the magnetic recording system. The equalizer characteristics are such that the FM signal band of 7 to 31 MHz is centered on the broken line, and the parts outside the band are attenuated.

Next, the frequency characteristics of the cosine equalizer 14 are shown in FIG.

The cosine equalizer 14 can linearly suppress/emphasize upper and lower sidebands centering on the carrier wave. The signal whose loss in the magnetic recording system has been compensated for by the 10 equalizer 13 becomes a signal with a linearly sloped characteristic by the cosine equalizer 14, thereby realizing so-called slope transmission.

S/N by suppressing high frequencies with cosine equalizer 14
can be set high, and by emphasizing the high range, it is possible to increase the inversion margin.

These adjustments are made based on the stability of the magnetic recording system and the like. A conceptual diagram of the circuit of the cosine equalizer 14 is shown in FIG. In FIG. 6, 31 is a multiplier with coefficient a, 32
A, 32B is a current source, 33 is a delay line (by amount of delay), 3
4 is a matching resistor of the delay line 33. Since the delay line 33 is terminated on only one side, the signal is reflected on the unterminated side, resulting in the following characteristic.

When the delay amount τ is set to 13 ns, the characteristics shown in FIG. 4 are obtained.

When the coefficient a is positive, it has a characteristic of suppressing the high frequency range, and when it is negative, it has a characteristic of emphasizing the high frequency range. This coefficient a is configured to be able to be controlled externally using a DC potential, and as will be described later, automatic equalization is performed by changing the value of the coefficient a.

Next, the frequency characteristics of the sideband suppression equalizer 15 are shown in FIG.

The sideband suppression equalizer 15 suppresses/emphasizes the upper and lower sidebands of the carrier wave at the same rate. This is apparently equivalent to changing the degree of modulation of FM, and can change the frequency characteristics after demodulation. Further, by suppressing the upper side band wave and the lower side band wave, a large amount of inversion margin can be obtained. Similar to the cosine equalizer 14 described above, the adjustment of this sideband suppression equalizer 15 is also set in consideration of the stability of the magnetic recording system, etc., so as to reduce image quality deterioration.

A conceptual diagram of the circuit of the sideband suppression equalizer 15 is shown in FIG.

This is done by adding a current source 32C and a coefficient 2a to the circuit shown in FIG.
This configuration includes a multiplier 31A.

The 8-force signal e0 is expressed by the following equation.

When the delay amount is 26.3 ns, the characteristics shown in FIG. 5 are obtained.

When the coefficient a is negative, the characteristic suppresses sideband waves, and when the coefficient a is positive, the characteristic emphasizes the sideband waves. Similar to the cosine equalizer 14, the coefficient a can be controlled externally using a DC potential.

Now, in Figure 2, the three types of equalizers (10
Equalizer 13, cosine equalizer 14, sideband suppression equalizer 1
5), from the signal whose loss in the magnetic recording system has been compensated for,
Information corresponding to equalization error fluctuations is obtained, and the cosine equalizer 14 and sideband suppression equalizer 15 are controlled based on the information.

In the present invention, information corresponding to equalization error fluctuation is transmitted to the reproduced FM
Extract from the amplitude value of the signal. As shown in FIG. 2, the FM signal of the equalizer 10 is subjected to AM detection by the AM detector 16, and then sampled and held by the sample and hold (S/H) circuit 17. D)
A/D conversion is performed by the converter 18, and input into the CPL 119, and the CPU 19 calculates the control voltage of the coefficient a of each of the cosine equalizer 14 and the sideband suppression equalizer 15, and the D/A converter 20.21 The signals are each subjected to D/A conversion and input to each multiplier of each equalizer 14 and 15.

Next, the signal waveform used for automatic equalization and the operation of automatic equalization using it will be explained below.

In order to obtain information corresponding to the equalization error fluctuation from the FM signal of the equalizer, one (horizontal)
A signal waveform of a video level (hereinafter referred to as a ramp waveform) that continuously changes between synchronization units (hereinafter referred to as H units) is used.

This ramp waveform is recorded at a fixed rate with respect to the video signal, for example, in units of IHH within a switching point period as shown in FIG.

Now, when this ramp waveform is FM modulated, as the video level changes from black to white, the carrier frequency increases to 16MHz.
The frequency changes from 22MHz to 22MHz. The envelope of the reproduced FM signal of the ramp waveform observed at the output of FQ convener 9 is
Shown in Figure (b). Here, since the time length of the H unit is much longer than the carrier wave frequency, the ramp waveform FM signal is composed of only the carrier wave, and almost no sideband waves are generated. Therefore, the shape of the envelope in Figure 8(b) (the amplitude is thick at the black level (and small at the white level) is the 16M frequency characteristic of the magnetic recording system obtained from recording and reproduction of a single frequency.
Corresponds to the Hz to 22 MHz portion. Since the 10 equalizer 13 creates the inverse characteristics of this magnetic recording system, the output of the 10 equalizer 13 provides a flat envelope as shown in FIG. 8(c). Furthermore, by setting the initial values of the coefficients a of each of the cosine equalizer 14 and the sideband suppression equalizer 15 to zero, the total output of the equalizers can also be adjusted as shown in FIG.
A flat envelope is obtained as shown in C). To simplify the explanation below, consider a case where the initial values of the coefficients a of the two equalizers are both zero.

Now, if the characteristics of the magnetic recording system change due to wear of the magnetic head, etc., the envelope of the ramp waveform after equalization will no longer be flat, and equalization error fluctuations will occur corresponding to the changes in the characteristics of the magnetic recording system. , which causes deterioration in image quality after demodulation.

Therefore, the envelope of the equalized signal is measured, and the variation in characteristics of the magnetic recording system is automatically adjusted from that value.

In the equalizer controller 11 of FIG. 2, the output of the sideband suppression equalizer 15 is envelope-detected, sampled and held, A/D converted, and read into the CPU 19. Here, the location where the envelope is sampled is shown in FIG. 8(a).

The sampling point is the black level (
16MHz) ■ Gray level (19MHz) O white level (22Ml(z)) Based on the measured values of these three places, CPU1
9, the equalizer control value is calculated.

First, the calculation formula corresponding to the cosine equalizer 14 is shown in formula (3).

0-■ ...(3) 22MH
The change in the slope of the frequency characteristic of the magnetic recording system compensated by the cosine equalizer 14 can be calculated from the difference between O, which is the output of The coefficient a of the cosine equalizer 14 is controlled through the D/A converter 20 so that the value (zero in this case) is obtained.

In addition, the level difference between the carrier wave and the band wave that can be compensated by the sideband suppression equalizer 15 can be calculated from the difference between the average of Equation 4 and 0 corresponding to the sideband suppression equalizer 15. ,
The coefficient a of the sideband suppression equalizer 15 is controlled through the D/A converter 21 so that this value becomes the initial value (zero in this case).

As described above, it is possible to configure an automatic equalizer that is compatible with changes in characteristics of the magnetic recording system, and it is possible to prevent image deterioration due to changes over time.

[Other Examples]

The automatic equalization process described above is achieved by using a video level signal waveform (hereinafter referred to as a staircase waveform) that changes stepwise between IH units, rather than a ramp waveform (as shown in Fig. 10). can also be achieved.

In this case as well, by sampling the envelope at three locations: ■black level, ■gray level, and 0 white level, using equations (3) and (4), the cosine equalizer 14,
Each coefficient a of the sideband suppression equalizer 15 can be controlled.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to construct an equalizer that does not deteriorate image quality even with changes over time.

[Brief explanation of drawings]

Figure 1 is a block diagram of an embodiment of the present invention, Figure 2 is a block diagram of the automatic equalizer section in the same embodiment, Figure 3 is a diagram showing the frequency characteristics of the LC equalizer, and Figure 4 is a cosine diagram. Figure 5 is a diagram showing the frequency characteristics of the equalizer. Figure 6 is a conceptual diagram of the cosine equalizer circuit. Figure 7 is the sideband suppression equalizer. Figure 8 shows the ramp waveform and its envelope; Figure 9 shows the ramp waveform and video signal waveform within the switching point period; Figure 1O shows the staircase waveform and its envelope. FIG. ■...FM modulator, 2...Recording amplifier, 3.7...Rotary transformer, 4.6...Magnetic head, 5...Magnetic tape, 8...Reproduction amplifier, 9... -FQ compensator, 10... Equalizer, 11... Equalizer controller, 12... FM demodulator, 13... LC equalizer, 14... Cosine equalizer, 15 ...Sideband suppression equalizer, 16...AM detector, 17...Sample and hold circuit, 18...A/D converter, 19...cpu. 20, 21... D/A converter, 31... Multiplier, 32... Current source, 33... Delay line, 34... Matching resistance for delay line. OIO20304050 Pl 5N W (MHz) Fig. 3 Pl Otokosami ) et al. C (MHz) Fig. 4 1t15'1. * (MHz) Fifth cause ■ ■ ■ (b) −−−−−−−(C) □−
□−□−□−−□−1 Figure 8

Claims (1)

[Claims] 1) Reproducing means for reproducing a low carrier wave FM recording signal recorded on a recording medium, a reproducing equalizer for waveform equalizing the reproduced FM signal from the reproducing means, and modulation in the signal from the reproducing equalizer. An image reproducing apparatus comprising: a detection means for detecting an envelope of a portion where the level of a signal changes; and means for controlling the reproduction equalizer based on a detection result of the detection means.