JPH04293379A - Picture recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent deterioration in picture quality due to a secular change by obtaining information corresponding to residual equalization error fluctuation from an amplitude of a reproduced burst signal so as to apply automatic adjustment control to a reproduction equalizer based on the information. CONSTITUTION:A band pass filter(BPF) 22 of an equalizer controller 11 extracts only a burst signal from an output (d) of an FM demodulator 12. The output is subject to envelope detection by an AM detector 23. The detected signal is sampled and held by a sample-and-hold circuit 24 and an A/D converter 25 converts the result into a digital signal. A CPU 19 compares an amplitude (f) of a read burst signal from the A/D converter 25 with a predetermined specified value. Then a coefficient (b) of a side band suppression equalizer 15 of an equalizer 10 is variably controlled through a D/A converter 21 so that the difference is made zero. That is, when the amplitude of the burst signal gets larger, the side band is suppressed and when the amplitude of the burst signal is small, the side band is emphasized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording/reproducing apparatus such as a VTR using a low carrier frequency FM recording method, and more particularly to an automatic equalization technique in the reproducing system.

0002

[Prior art] Conventionally, low carrier wave FM (frequency modulation)
In a VTR (video tape recorder) that uses a recording system, the playback system uses a playback F in order to compensate for losses in the magnetic recording system.
Waveform equalization processing is performed on the M signal. In particular, in VTRs that require high image quality, such as professional VTRs, the video signal band is wide, and the deviation (frequency shift) is set wide to obtain a high S/N (signal-to-noise ratio). Recording and reproduction of FM signals with wide deviations is achieved by highly accurate waveform equalization.

0003

However, in the conventional example as described above, there is a problem to be solved in 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 increase equalization errors, causing significant deterioration in image quality.

SUMMARY OF THE INVENTION In view of the above points, an object of the present invention is to provide an image recording and reproducing apparatus that can prevent image deterioration due to changes over time.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a video signal in which a synchronization signal and a burst signal for time axis correction during playback are inserted into a period other than an effective video period, using a low carrier frequency. An image recording and reproducing apparatus having a recording system for recording with FM modulation, comprising a reproducing means for reproducing the video signal recorded by the recording system as an FM signal, and a reproducing means for compensating for loss in the recording system. FM played
A reproduction equalization means that performs waveform equalization processing on the signal, and an F that inputs the output of the reproduction equalization means and demodulates it to the original video signal.
Information corresponding to residual equalization error fluctuation is obtained from the amplitude value of the reproduction burst signal demodulated by the M demodulation means and the FM demodulation means, and the equalization coefficient of the reproduction equalization means is variably controlled based on the information. The invention is characterized in that it is equipped with a control means.

Further, in one aspect of the present invention, the reproduction equalization means has an inverse frequency characteristic to the frequency characteristic of the recording system, and includes an LC equalizer for compensating the loss of the recording system, a cosine equalizer that realizes slope transmission by linearly suppressing or emphasizing upper and lower sideband waves according to a coefficient a;
a sideband suppression equalizer that changes the degree of modulation of FM by suppressing or emphasizing upper and lower sidebands at the same rate around the carrier frequency according to a coefficient b; The present invention is characterized by comprising an equalizer controller that variably sets the coefficient a and the coefficient b based on information corresponding to residual equalization error fluctuations.

[0007]

[Operation] In the present invention, a synchronization signal (hereinafter referred to as an H synchronization signal) and a burst signal (hereinafter referred to as a burst signal) used for time axis correction during playback are inserted into a period other than the effective video period. A video signal is recorded with a low carrier FM, and information corresponding to residual equalization error fluctuation is obtained from the amplitude value of the reproduced burst signal that is subsequently reproduced, and automatic adjustment control of the reproduction equalizer is performed based on that information. This makes it possible to prevent image quality from deteriorating due to changes over time.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic circuit configuration of a VTR according to an embodiment of the present invention.

During recording, the input signal (modulated signal) input to the input terminal is FM modulated with a low carrier FM by the FM modulator 1, and then amplified by the recording amplifier 2, and then sent to the rotary transformer (rotary transformer). 3 and then written onto the magnetic tape 5 by the magnetic head 4. Specific examples of carrier wave frequencies for FM modulation at this time are shown in Table 1 below. Here, considering FM modulation where the band of the modulated signal is 12 MHz and the maximum deviation after emphasis is about 20 MHz, F
The M signal band is approximately 7 MHz to 31 MHz.

[0011]

[Table 1]

The above modulated signal is shown in FIG. 8 (described later).
The synchronization signal (
This is a video signal into which a burst signal used for time axis correction during playback is inserted.

On the other hand, during reproduction, the signals recorded on the magnetic tape 5 are read out by a reproduction magnetic head 6, passed through a rotary transformer 7, and amplified by a reproduction amplifier 8.
An FQ compensator (resonance characteristic compensation circuit) 9 corrects the frequency characteristics of the reproduction system. Since this FQ compensator 9 creates a resonant characteristic opposite to that of the reproducing circuit formed by the magnetic head 6, rotary transformer 7, regenerative amplifier 8, etc., the output signal of the FQ compensator 9 is magnetically smaller than that of the FM modulator 1. This becomes a signal that has suffered only losses in the recording system. The output of the FQ compensator 9 is compensated for losses in the magnetic recording system by an equalizer 10, demodulated by an FM demodulator 12, and output to an output terminal.

At this time, the equalizer controller 11 obtains information corresponding to the residual equalization error fluctuation from the output of the equalizer 10 and the output of the FM demodulator 12, and controls the equalizer 10 based on this information. control and automatic equalization.

As shown in FIG. 2, the equalizer 10 described above has L
It is composed of three types of equalizers: a C (inductance-capacitance) equalizer 13, a cosine equalizer 14, and a sideband suppression equalizer 15. The LC equalizer 13 uses an internal 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, thereby compensating for losses in the magnetic recording system. In this embodiment, a rectangular wave is used as the recording waveform of the FM signal, so even under the wide deviation conditions mentioned above, the LC equalizer 1
3, it is possible to compensate the magnetic recording system.

FIG. 3 shows an example of the frequency characteristics of the LC equalizer 13.
Shown below. The solid line in FIG. 3 is the characteristic of the LC equalizer 13, and the broken line is the inverse characteristic of the frequency characteristic of the magnetic recording system. This equalizer characteristic is such that only the necessary band, centering on the FM signal band of 7 MHz to 31 MHz, matches the inverse characteristic of the magnetic recording system shown by the broken line, and the wide area outside the necessary band is gently attenuated.

Next, the frequency characteristics of the cosine equalizer 14 are shown in FIG. The cosine equalizer 14 can linearly suppress or emphasize upper and lower sidebands around the carrier frequency. The FM signal whose loss in the magnetic recording system has been compensated by the LC equalizer 13 becomes linearly sloped by the cosine equalizer 14, thereby realizing so-called slope transmission. By suppressing the high frequency range with the cosine equalizer 14, the S/N ratio can be set high, and by emphasizing the high frequency range, the inversion margin can be increased. These suppression/emphasis adjustments are made in consideration of the stability of the magnetic recording system, etc., so as to minimize image quality deterioration.

An example of a conceptual circuit configuration of the cosine equalizer 14 is shown in FIG. In FIG. 5, 31 is a multiplier, 32 is a current source, 33 is a delay line, and 34 is a matching resistor for the delay line 33. Since the delay line 33 is terminated only on one side, the signal is reflected on the unterminated side, resulting in an output characteristic expressed by the following equation.

[0019]

[Math 1]

[0020] However, ei is the input value, eo is the output value,
a is a multiplication coefficient, ω is a carrier frequency, and τ is a delay amount in the delay line 33. When this delay amount τ is set to 13.2 ns, the characteristics shown in FIG. 4 are obtained. When the coefficient a is positive, it has a characteristic of suppressing high frequencies, and when it is negative, it has a characteristic of emphasizing high frequencies. The value of the coefficient a can be controlled from outside the cosine equalizer 14 using a DC potential, and as will be described later, the value of the coefficient a is changed by the equalizer controller 11 to perform automatic equalization.

Next, the frequency characteristics of the sideband suppression equalizer 15 are shown in FIG. The sideband suppression equalizer 15 suppresses or emphasizes upper and lower sidebands at the same rate around the carrier frequency. This is apparently equivalent to changing the degree of modulation of FM, and the FM demodulator 12 can change the frequency characteristics after demodulation. Further, as shown by the solid line in FIG. 6, 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 suppression/emphasis adjustment of the sideband suppression equalizer 15 is also set in consideration of the stability of the magnetic recording system, etc., so that image quality deterioration is minimized.

An example of a conceptual circuit configuration of the sideband suppression equalizer 15 is shown in FIG. In FIG. 7, 41A is a multiplier that multiplies 2b (b is a coefficient), 41B is a multiplier that multiplies b, 42A, 42B, and 42C are current sources, 43 is a delay line with a delay amount τ, and 44 is a delay line 43 matching resistor. Here, when ei is an input value, eo is an output value, and ω is a carrier frequency, the output characteristic of the sideband suppression equalizer 15 is expressed by the following equation.

[0023]

[Math 2]

When the above delay amount τ is 26.3 ns, FIG.
The following characteristics are obtained.

When the coefficient b is negative, the characteristic is to suppress sideband waves, and when the coefficient b is positive, the characteristic is to emphasize the sideband waves. Similar to the cosine equalizer 14, the coefficient b is input from the outside of the sideband suppression equalizer 15 to the equalizer controller 11 in DC units.
The structure is such that it can be controlled by

For the cosine equalizer 14 and sideband suppression equalizer 15 described above, the equalizer controller 11 calculates equalization error fluctuations from the output of the sideband suppression equalizer 15 and the output of the FM demodulator 12. The equalizer coefficient values a and b are variably controlled based on this information, thereby realizing automatic equalization.

In this embodiment, the equalizer controller 11 obtains information corresponding to equalization error fluctuations from the H synchronization signal and the burst signal. The signal waveform of that part is shown in Figure 8 (
Shown in A). This burst signal is processed by a TBC (time base collector) to remove time axis fluctuations caused by recording and playback.
This signal is a reference signal for generating a clock, and six 4.8 MHz sine waves with amplitudes ranging from black level to white level are inserted. FIG. 8B shows an envelope waveform observed at the output of the FQ compensator 9 in FIG. 1 by recording and reproducing the burst signal shown in FIG. 8A. In a magnetic recording system, the high frequency range is suppressed, so the envelope at the synchronization tip where the carrier frequency is low is the largest, and the envelope at the white part is the smallest.

Since the LC equalizer 13 creates an inverse characteristic of the magnetic recording system in order to compensate for the loss of the magnetic recording system, the L
At the output of the C equalizer 13, a flat envelope is obtained as shown in FIG. 8(C). In addition, the cosine equalizer 14
By setting the initial values of the coefficients a and b of the sideband suppression equalizer 15 to zero, the entire output of the equalizer 10 has a flat envelope as shown in FIG. 8(C). can get. In the following, to simplify the explanation, we will consider a case where the initial values of the coefficients a and b of the two equalizers 14 and 15 are both zero. The reproduced FM signal whose loss in the magnetic recording system has been compensated for by the equalizer 10 is demodulated by the FM demodulator 12.
As a result, a signal with the original waveform as shown in FIG. 8(A) is obtained.

Now, the equalizer controller 11 obtains information corresponding to the equalization error fluctuation from the output c of the sideband suppression equalizer 15 and the output d of the FM demodulator 12, and performs automatic equalization of the equalizer 10. In performing control, in this embodiment, (i) information F corresponding to equalization error fluctuation is obtained from the output c of the sideband suppression equalizer 15, and based on this information F, the cosine equalizer 14 is adjusted. First loop controlling coefficient a (ii) FM demodulator 16
Automatic equalization control is performed using two loops, including a second loop that obtains information G corresponding to the equalization error fluctuation from the output d of conduct.

First, referring to FIG. 2, information F corresponding to the equalization error fluctuation is obtained from the output c of the sideband suppression equalizer 15 in (i).
The configuration and operation of the first loop that controls the coefficient a of the cosine equalizer 14 based on this information F will be explained. Here, the cosine equalizer 14 to be controlled has a frequency characteristic that linearly slopes the relative gain with respect to the frequency of the carrier wave, as shown in FIG. By sensing this, it is possible to know the equalization error variation that can be compensated by the cosine equalizer 14. That is, in this embodiment, attention will be paid to two parts, the leading edge part of the H synchronization signal shown in FIG. 8A and the back porch part between the synchronization signal and the burst signal shown in part II. If the characteristics of the magnetic recording system change due to wear of the magnetic heads 4, 6, etc., the envelope after equalization by the equalizer 10 will no longer be flat, but this will change as shown in FIG. 8(C). Automatic equalization control is performed by adjusting the value of coefficient a so as to maintain a flat state.

Therefore, in FIG. 2, the sideband suppression equalizer 1
The output c of 5 is subjected to envelope detection by an AM (amplitude modulation) detector 16, and this is detected by a sample hold circuit (S/H) 1.
7, the sample is held and then converted into a digital value by an A/D (analog-to-digital) converter 18, and this digital value e is read into a CPU (central processing unit) 19. Here, the points at which the envelope is sampled are two points: the tip (14 MHz) of the H synchronization signal (■) in FIG. 8 and the back porch (19 MHz) (■) in FIG. 8. The CPU 19 performs subtraction using the following equation for the measured values (■) and (2) at these two locations.

[0032]

[Equation 3] F=■−■ In this way, by calculating the difference F between the 19MHz output ■ and the 14MHz output ■ using the CPU 19,
Changes in the slope of the frequency characteristics of the magnetic recording system that can be compensated for by the cosine equalizer 14 can be calculated. This operation may be realized by table lookup. This calculation result is converted into an analog value coefficient a by a D/A (digital/analog) converter 20 and inputted to the cosine equalizer 14, whereby the value of the above formula F becomes the initial value (zero in this case). The equalization coefficient a of the cosine equalizer 14 is controlled so that.

Next, (ii) the output d of the FM demodulator 16
Obtain the information f corresponding to the equalization error fluctuation from
The configuration and operation of the second loop that controls the coefficient b of the sideband suppression equalizer 15 based on the following will be described. Here, the sideband suppression equalizer 15 to be controlled has a frequency characteristic that suppresses or emphasizes the upper sideband and the lower sideband at the same rate with respect to the carrier wave, as shown in FIG. This appears to be
This is equivalent to changing the modulation degree of FM. Therefore,
By sensing the amplitude value of the burst signal with the equalizer controller 11, it is possible to know the equalization error fluctuation that can be compensated by the sideband suppression equalizer 15. Then, when the amplitude of the burst signal becomes large, sideband waves are suppressed, and when the amplitude of the burst signal becomes small, the sideband waves are emphasized.

Therefore, in FIG. 2, the output d of the FM demodulator 12 is filtered by a band pass filter (BPF) 22 having a characteristic of passing 4.8 MHz, which is the frequency of the burst signal.
Only the 4.8MHz signal is extracted from the 4.8MHz signal. After that, B.P.
The output of F22 is envelope-detected by AM detector 23, and the detected burst signal is sent to sample-hold circuit 2.
4, and then the value f converted into a digital value by the A/D converter 25 is read into the CPU 19. CPU
At step 19, the amplitude value of the read burst signal is compared with a predetermined value, and the coefficient b of the sideband suppression equalizer 15 is variably controlled through the D/A converter 21 so that the difference value G becomes zero. do.

In this way, since the set values of the coefficients a and b used in the equalizer are variably controlled based on the reproduction burst signal, the envelope after equalization remains flat even if the characteristics of the magnetic recording system change. This stabilizes the quality of the reproduced image.

[0036]

[Effects of the Invention] As explained above, according to the present invention,
In an image recording and reproducing apparatus using a low carrier FM recording method, a video signal into which an H synchronization signal and a burst signal are inserted is recorded and reproduced, and information corresponding to equalization error fluctuations is obtained from the amplitude value of the reproduced burst signal. Since automatic equalization is achieved by controlling the equalizer based on this information, it is possible to prevent image quality deterioration due to changes over time.

[Brief explanation of the drawing]

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

FIG. 2 is a block diagram showing details of a circuit configuration of an automatic equalization processing portion in FIG. 1;

FIG. 3 is a characteristic diagram showing the frequency characteristics of the LC equalizer in FIG. 2;

FIG. 4 is a characteristic diagram showing frequency characteristics of the cosine equalizer in FIG. 2;

FIG. 5 is a circuit diagram showing the circuit configuration of the cosine equalizer of FIG. 2;

FIG. 6 is a characteristic diagram showing the frequency characteristics of the sideband suppression equalizer in FIG. 2;

FIG. 7 is a circuit diagram showing a circuit configuration of the sideband suppression equalizer in FIG. 2;

FIG. 8 is a waveform diagram showing the waveforms of the H synchronization and burst signal portions and their envelopes in the embodiment of the present invention.

[Explanation of symbols]

1 FM modulator 2 Recording amplifier 3, 7 Rotary transformer 4, 6 Magnetic head 5 Magnetic tape 8 Reproducing amplifier 9 FQ compensator 10 Equalizer 11 Equalizer controller 12 FM demodulator 13 LC equalizer 14 Cosine equalizer 15 Sideband suppression equalizer 16, 23 AM detector 17, 24 Sample hold circuit 18, 25 A/D converter 19 CPU 20, 21 D/A converter 22 Band pass filter 31, 41A, 41B Multiplier 32, 42A, 42B, 42C Current source 33, 43
delay line

Claims (2)

[Claims] 1. An image recording and reproducing apparatus having a recording system that records a video signal in which a synchronization signal and a burst signal for time axis correction during reproduction are inserted in a period other than an effective video period using low carrier FM modulation, Reproducing means for reproducing the video signal recorded by the recording system as an FM signal; and reproducing means for performing waveform equalization processing on the FM signal reproduced by the reproducing means to compensate for loss in the recording system. equalization means;
FM demodulation means for inputting the output of the reproduction equalization means and demodulating it to the original video signal; and obtaining information corresponding to residual equalization error fluctuation from the amplitude value of the reproduction burst signal demodulated by the FM demodulation means. , and control means for variably controlling the equalization coefficient of the reproduction equalization means based on the information. 2. The reproduction equalization means has a frequency characteristic opposite to that of the recording system, and has an L
C equalizer, a cosine equalizer that achieves slope transmission by linearly suppressing or emphasizing upper and lower sidebands around the carrier frequency according to the coefficient a, and a cosine equalizer that realizes slope transmission by linearly suppressing or emphasizing upper and lower sidebands around the carrier frequency, and a sideband suppression equalizer that changes the degree of modulation of FM by suppressing or emphasizing sidebands at the same rate according to coefficient b, and the control means transmits information corresponding to the residual equalization error fluctuation. 2. The image recording and reproducing apparatus according to claim 1, further comprising an equalizer controller that variably sets the coefficient a and the coefficient b.