JPH036181A - Device for discriminating a recording system of fm modulation video signal - Google Patents

Abstract

PURPOSE:To automatically discriminate the recording system for an FM modulation video signal read from a recording medium by detecting a level difference of a pedestal level and a sink chip level detected by a first and a second detecting means by a differential means, and comparing it with a reference level. CONSTITUTION:A signal for showing a pedestal level detected by a sample holding SH circuit 21, and a signal for showing a sink chip level detected by an SH circuit 22 are applied to a positive input terminal of a differential amplifier 23 through a resistance R1, and a negative input terminal of the differential amplifier 23 through a resistance R2, respectively. By this differential amplifier 23, a level difference of a pedestal and a sink chip is detected. An output of the differential amplifier 23 is given to a positive input terminal of a comparator 24. To a negative input terminal of this comparator 24, a reference level VR is applied. Accordingly, at the time of a normal band, and at the time of a high band, a signal of an L level, and a signal of an H level are outputted from the comparator 24, respectively. An output signal of the comparator 24 becomes a high band/normal band discriminating signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention An FM modulated video signal is read from a recording medium and then demodulated, and a pedestal level and a sync urn chip level are respectively detected in the synchronization signal portion of the demodulated video signal. Find the level difference between the pedestal level and the sink tip e level.

The type of recording method of the video signal is determined by utilizing the fact that this level difference differs depending on the recording method.

Technique 47 Minutes Invention 0 Background 1 Width 1 Male 1 Piece 1 This invention is a recording medium that uses carrier waves of different frequencies to perform FM modulation when recording a video signal on a recording medium. The present invention relates to a device for determining which type of recording method a video signal read from a video signal is based on, for example, a device for automatically determining between a normal band recording method and an I/I band recording method for a still video signal.

Conventional technology and its problems When recording still video signals on high-density magnetic floppy disks using electronic still cameras (still video cameras) and other recording devices, there are two recording methods: normal band recording and high band recording. There is a method.

A still video signal consists of a luminance signal (Y signal) and a color signal (C signal) (generally color difference signals R-Y and B-Y). In the normal band recording method, a carrier wave with a center frequency of 7 MHz is FM modulated by a luminance signal Y, and this FM modulated wave is abbreviated as Y-RF multiplied signal).One color difference signal R-Y, B-
Frequency 1.2 MHz by Y, IJ
FM modulates the MHz carrier wave and converts these FM modulated waves into C
-RF double signal), these Y-RF, C-RF
The signals are mixed and recorded on a video floppy track. These Y-RF multiplied signal C-RF multiplied signal frequency allocations are shown in FIG. 6(A). Y-R
F times signal sync chip (synchronization tip) frequency is 6MHz
, the white peak (self-peak) frequency is 7.5MHz
, the frequency deviation is 1.5 MHz.

In the /1 band recording system for recording high-resolution still video signals, the center frequency of the carrier wave for FM modulation of the luminance signal Y is set to 9 MHz. Figure 6 CB)
As shown in the figure, the Y-RF multiplied signal sync chip frequency is 7
．． 7MHz, white peak frequency is 9.7MHz
, the frequency deviation is 2MHz. This is the same as the case of the C-RF multiplied signal normal band.

As described above, when the recording method of still video signals is different, the reproduction method is also different. Therefore, in a device capable of reproducing both the normal band and the high band, a circuit section dedicated to the normal band and a circuit section dedicated to the high band are provided. It is not specified in which method the still video signal is recorded on the video floppy installed in the playback device or on each track of the video floppy (especially video signals recorded using the normal band recording method and/or video signals recorded using the normal band recording method). (If video signals recorded using the 1-band recording method are mixed), the recording method is determined from the video signal read from the video floppy in the playback device, and the dedicated circuit section is determined based on the result of this determination. It is necessary to make a switch. This is why it is necessary to automatically determine the recording method of the RF video signal.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION An object of the present invention is to provide a device that can automatically determine the recording format from an FM modulated video signal read from a recording medium.

Structure 1 of the Invention Functions and Effects This invention provides a method for determining which type of video signal is recorded on a recording medium by any one of a plurality of recording methods in which FM modulation is performed using carrier waves of two different frequencies. This is a device that determines whether the recording method is based on a recording method, and includes a reading head that reads an FM modulated video signal from a recording medium, a demodulation circuit that demodulates the FM modulated video signal read by the reading head, and a demodulated video signal. A first detecting means for detecting a pedestal level; a second detecting means for detecting a sync chip level of the demodulated video signal; a sync chip level detected by the first and second detecting means; - Differential means for detecting a level difference with a chip-level, and by comparing the level difference detected by said differential means with a predetermined reference level.

It is characterized by comprising means for determining the type of recording method.

Signals FM modulated using carrier waves of different frequencies have different frequency deviations. For example, the frequency deviation of the above-mentioned normal band recording method is 1.5 MHz, and that of the high band recording method is 2 MHz.
It is z. However, when considering the difference between the frequency at the pedestal level and the frequency at the sync tip level, the ratio of this frequency difference to the frequency deviation is fixed at a constant value in all recording methods. Therefore, the above frequency difference has different values depending on the recording method.

On the other hand, an FM demodulation circuit has a characteristic (generally linear characteristic) of outputting a voltage according to the frequency of an input signal. Therefore, the frequency difference between the pedestal level and the sync tip level appears as a level difference in the output voltage of the FM demodulation circuit.

In this invention, first. A pedestal level and a sync tip φ level in the synchronization signal portion of the demodulated video signal are detected by the second detection means, respectively;
Furthermore, these level differences are determined by differential means. Since this level difference differs depending on the recording method, it is possible to determine the recording method by comparing the detected level difference with a reference level that is intermediate between the level differences among the recording methods to be determined.

Hereinafter, an embodiment in which the present invention is applied to distinguish between the above-mentioned normal band recording and high band recording of still video signals will be described in detail.
Needless to say, the present invention can also be applied to determining the recording format of a movie video signal recorded on a video tape, and to determining the recording format of other video signals.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a block diagram showing a part of a reproducing apparatus for a still picture signal recorded on a video floppy, particularly a part of a recording system discrimination circuit.

FM on video floppy (magnetic recording medium) (path shown)
The modulated and recorded still video signal (hereinafter referred to as the RF multiplied signal) is read by the magnetic head 1O and then given to the preamplifier 11. The reproduced RF signal amplified by the amplifier 11 is supplied to the equalizer 12 to compensate so that the upper and lower sideband components are approximately equal, and is supplied to the trap circuit 13. The trap circuit 13 is a high-pass filter circuit that removes the C-RF multiplied signal from the reproduced RF signal and passes the Y-RF multiplied signal. The amplitude of the Y-RF multiplied signal output from the trap circuit 13 is limited by the limiter 14 and then provided to the FM demodulation circuit 15 . Demodulation circuit 1
The luminance signal Y obtained by demodulating the signal Y is given to a low-pass filter 16. Low pass filter 16
is for removing the carrier wave component of FM modulation,
The cutoff frequency and wave number are set to 6 to allow the high frequency components of the high band luminance signal Y to pass through sufficiently.
It is set to about MHz. The demodulated luminance signal Y output from the low-pass filter 16 is given to the automatic gain side 8 amplifier circuit 17, the first sample-and-hold circuit 21, and the second sample-and-hold circuit 22, respectively.

FIG. 3 shows the characteristics of the FM demodulation circuit 15. FM
The demodulation circuit has a portion where the output voltage changes linearly with respect to the frequency of the input signal, and this portion is used for FM demodulation. As mentioned above, the sync chip frequency of the normal band recording method is 6 MHz, and the white Φ peak frequency is 7.5 MHz. The output voltage level of the demodulation circuit 15 for these frequencies is expressed as g.
Let N3'gNl. Further, the demodulated output corresponding to the pedestal (black) level frequency of the normal band is assumed to be gN2. Similarly, the output levels of the demodulation circuit 15 corresponding to the sync chip frequency (7.7 MHz), pedestal level frequency, and white peak frequency (9.7 MHz) of the high band recording method are expressed as g and g, respectively.
, g.

83 H2 Old On the other hand, as shown in Figure 4, the frequency difference a between the white peak and the sync tip, the frequency difference between the white peak and the pedestal level, and the frequency difference between the pedestal level and the sync tip are If the frequency difference between is C, then NT
According to the SC format, these frequency differences a, b,
The ratio of c is.

Regardless of the type of recording method, a:b:(mlHO,7
14: It is determined to be 0.286.

As mentioned above, the frequency deviation of the normal band (
This is expressed as aN) is 1.5MHz, and the high band frequency deviation (this is expressed as an) is 2.0M.
Since it is Hz, it is a N/an -3/4. Assuming that the characteristics of the demodulation circuit 15 are linear, "g
Nl-gNa)/(gHl "l-13)" = 374
becomes.

Pedestal level and sync level in normal band
Let the frequency difference between the chip and the pedestal Φ level in the band be 'H.As explained with reference to Figure 4, c/a is independent of the recording method. Because it is constant” N /aN =
CH/aH”c/a. a/a n =
3. / Because it is 4.

CN/c, 1-3/4. If this relationship is expressed by the output voltage difference of the demodulation circuit 15, c / c n
−(g −g ) / (gH2−gNa) −3
/4 and N2 N3.

In this invention, (g N2- g N3) or (g11
2gH3) was detected. Also ( g N2 ”
A reference level VR between N3) and (gH2-gNa) is set in advance. Then, it was detected (gN2gN
3) or (g N2- g Ha) as the reference level VR
It is determined whether the recording method is normal band or high band by comparing with .

FIG. 2 shows the relationship between the synchronization signal portion of the luminance signal Y after demodulation and the sample pulses SPI and SF3 for sampling the pedestal Φ level and the sync tip level from this synchronization signal portion.

In FIG. 1, the timing generation circuit 20 generates the above-mentioned sample stage pulse SP1. SP2 is generated and applied to sample and hold circuits 21 and 22, respectively. As described above, the demodulated luminance signal Y is input to the sample and hold circuits 21 and 22, respectively. Sample/hold circuit 2
1 detects and holds the pedestal level (g or gH2) at the timing of the sample stage pulse SPI. The sample 2 hold circuit 22 sets the sync chip level (gNa or g+t) at the timing of the sample pulse SP2.
3) Detect and hold.

The pedestal signal detected by the sample and hold circuit 21
A signal representing the level is sent to the differential amplifier 23 via the resistor R1.
A signal representing the sync tip level detected by the sample and hold circuit 22 is applied to the negative input terminal of the differential amplifier 23 via a resistor R2. The differential amplifier 23 has a feedback loop in which an output signal is fed back to a positive input terminal via a resistor R4, and a negative input terminal is grounded via a resistor R3. By this differential amplifier 23, the pedestal φ
The level difference between the level and the sync tip level (g
-g) or (g82 ”N3) is detected and N
2 N3 Ru.

The output of the differential amplifier 23 is applied to the positive input terminal of the comparator 24. The reference level VR is applied to the negative input terminal of the comparator 24. therefore.

When it is a normal band, (gN2 gNa) <'
/R, so the comparator 24 outputs an L level signal /
When %iband, (g g) > VR N2
From N3, the comparator 24 outputs an H level signal, respectively. The output signal of the comparator 24 becomes a NO1 band/normal band discrimination signal.

As mentioned above, since the level of the output signal of the FM demodulation circuit 15 changes depending on the frequency of the input Y-RF signal, the output signal level is different between the normal band and the high band even if the signal is of the same image. This mainly appears as a difference in image brightness when the reproduced signal is displayed on a CRT display device. It is undesirable that the brightness of the screen varies depending on the recording method. An automatic gain control amplifier circuit 17 is provided to keep the level of the finally output luminance signal Y substantially constant regardless of the difference in recording method. The gain of this amplifier circuit 17 is controlled by the output signal of the differential amplifier 23. That is, when the output signal level of the differential amplifier 23 is high (high band), the gain of the amplifier circuit 7 becomes a relatively small value, and conversely, when the output signal level of the differential amplifier 23 is low ( normal band), amplifier circuit 1
The gain of 7 is switched to a relatively large value.

This makes it possible to make the potential level of the demodulated video signal constant, which varies depending on the recording method.

The luminance signal Y output from the automatic gain amplification circuit 17 has its high frequency components suppressed by the de-emphasis circuit 18, and then one is outputted as a luminance signal Y, and the other is given to the sync separation circuit +9. The synchronization separation circuit I9 extracts the synchronization signal from the luminance signal Y and supplies it to the timing generation circuit 20 as described above.

The sampling operation (generation of sample-pulses SP1...SP2) in the sample-and-hold circuits 21, 22 is performed in the portion of the hybrid synchronization signal, and may be performed only once or several times. Further, it may be performed every time a period of 1v has elapsed, or it may be performed only once during the regeneration of Totorafu.

The embodiment shown in FIG. 1 has an advantage in that one circuit can be simplified because only the gain of the amplifier circuit 17 is switched depending on the recording method determination result.

FIG. 5 shows a modification, in which the high band/normal band discrimination circuit shown in FIG. 1 is used as is.

In FIG. 5, the low-pass filter te and automatic gain amplification circuit 17 are not provided, and instead, a high-band low-pass filter 31 (cutoff frequency: 6 MHz) and a normal band low-pass filter 32 (cutoff frequency: 4.5 MHz) are connected in parallel and can be switched by a changeover switch 34. The changeover switch 34 is controlled by a high band/normal band discrimination signal. Low pass filter 31
An attenuator 33 is connected to the rear stage. This is to make the high luminance signal level in the case of the high band method match the luminance No. 13 No. 1 Novel of the normal band method.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention. Figure 2 is a time chart showing the relationship between the luminance signal synchronization signal and sample pulse, Figure 3 is a graph showing the characteristics of the FM demodulation circuit, Figure 4 is a waveform diagram showing the luminance signal, and Figure 5 is a graph showing the characteristics of the FM demodulation circuit.
This figure is a block diagram showing a modification of the circuit shown in FIG. 1. FIGS. 6(A) and 6(B) are diagrams showing frequency allocation, where (A) shows normal band recording and (B) shows high band J recording, respectively. Fig. 2 10...Magnetic head. 15... Demodulation circuit. 21, 22...Sample/hold circuit. 23...Differential amplifier. 24... Comparator. that's all

Claims (1)

[Claims] Which type of recording method is used to record a video signal on a recording medium by any one of a plurality of recording methods that perform FM modulation using at least two types of carrier waves of different frequencies. The apparatus includes: a reading head for reading an FM modulated video signal from a recording medium; a demodulation circuit for demodulating the FM modulated video signal read by the reading head; and a circuit for detecting a pedestal level of the demodulated video signal. a second detection means for detecting a sync chip level of the demodulated video signal; a level between the pedestal level and the sync chip level detected by the first and second detection means; A recording method for an FM modulated video signal, comprising: differential means for detecting a difference; and means for determining the type of recording method by comparing the level difference detected by the differential means with a predetermined reference level. Device to determine.