JPH0325760A - Device for discriminating recording system of frequency modulated video signal - Google Patents

Abstract

PURPOSE:To automatically discriminate the kind of a recording system by integrating the output signal of a frequency demodulation circuit extending over a prescribed period of time, and comparing the level of the output signal with the reference level of a reference level setting means. CONSTITUTION:A luminance signal Y demodulated at a demodulation circuit 15 is supplied to an LPF 16, and a carrier component is eliminated, and is supplied to a de-emphasis circuit 17 and an integrator 19, respectively. The luminance signal Y of the integrator 19 is amplified at a transistor 23, and is outputted from an emitter-follower circuit 24. The signal Y is supplied to the positive input terminal of a comparator 21 via a switching circuit 22. Also, the reference level Vs is applied on the negative input terminal of the comparator 21. Thereby, since VN<Vs in normal-band recording, a signal of L level is outputted from the comparator 21, and a signal of H level from the comparator 21 in high-band recording since VN>Vs. In such a way, it is possible to automatically discriminate the high-band recording from the normal-band recording.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention An integral value of a part or all of an FM modulated video signal read from a recording medium is obtained. Taking advantage of the fact that this integral value differs depending on the recording method, the type of recording method of the video signal is determined by comparing the above integral value with a predetermined reference value.

BACKGROUND OF THE INVENTION TECHNICAL FIELD This invention relates to a recording method in which a video signal is recorded on a recording medium using one of two different frequency bands. The present invention relates to a device for automatically determining whether a still video signal is a normal band recording method or a high band recording method.

Conventional technology and its problems Electronic still ◆Recording methods for recording still video signals onto high-density magnetic floppy disks using cameras (still ●video ●cameras) and other recording devices include the normal band recording method and the normal band recording method. There is a recording 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 the luminance signal Y (this FM modulated wave is abbreviated as the Y-RF signal), and the color difference signals R-Y, B are
−Y with frequencies of 1.2 MHz and 1, respectively.
．． 3 MHz carrier wave is FM modulated (these FM modulated waves are abbreviated as C-RF signal). These Y-RF.
C-RF signals are mixed and recorded on a video floppy track. The frequency allocation of these Y-RF signals and C-RF signals is shown in FIG. 5(A). The synchronization tip frequency of the Y-RF signal is 6MHz, and the white peak frequency is 7.
5MHz, frequency deviation is 1.5MHz.

In the no-band recording method 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. As shown in Figure 5 (B), Y-RF signal sync ●Chip frequency is 7.7MHz, white ●Peak frequency is 9.7M
Hz, and the frequency deviation is 2 MHz.

The C-RF signal is the same as the normal band case.

As described above, when the still video signal recording method is y8, the reproduction method is also different. Therefore, in a device that can reproduce both normal band and high band,
A normal band dedicated circuit section and a high band dedicated circuit section are provided. It is not specified which method is used to record still video signals on the video floppy installed in the playback device or on each track of the video floppy (in particular, video signals recorded using the normal band recording method and high-speed video signals If video signals recorded using the band recording method are mixed), the playback device determines the recording method from the video signal read from the video e-floppy, and switches the dedicated circuit section based on the result of this determination. It is necessary to do it. This is why it is necessary to automatically determine the recording method of the RF video signal.

Summary of the Invention Object of the Invention The object of the present invention is to provide a device that can automatically determine the recording method from an FM modulated video signal read from a recording medium.

Structure, operation, and effects of the invention This invention. In an apparatus for determining whether a video signal read from a recording medium is one of two types of FM modulated video signals having different frequency bands, an FM demodulation circuit demodulating an FM modulated video signal read from a recording medium,
Integrating means for integrating the output signal of the M demodulation circuit over a predetermined period. The above two types of FM obtained from the above integration means
A recording method is determined by comparing the level of the output signal of the reference level setting means for outputting a reference level having an intermediate level between the output level of the modulated video signal and the integrating means and the reference level of the reference level setting means. It is characterized by comprising means for determining the type.

The integration operation period by the integration means may be limited to a specific portion of the synchronization signal of the video signal, or may be the entire period of vertical scanning of the video signal. The integrating means may have the role of de-emphasizing the pre-emphasized video signal, and in this case, the output level to be compared with the reference level may be sample data at a specific point in time. That is, the integration period may include a specific instant.

The FM demodulation circuit has a characteristic (generally linear characteristic) of outputting a voltage according to the frequency of the human input signal.

Since the frequency range of the FM modulated video signal differs depending on the recording method, the output demodulated signal level of the FM demodulation circuit also takes a different value depending on the recording method.

In this invention, the demodulation level of a particular portion of the FM modulated video signal or the average demodulation level is detected by the integrating means. By comparing the output level of this integrating means with a predetermined reference level, the type of recording method is automatically 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 luminance signal reproducing circuit and a recording method discriminating circuit.

Video floppy (magnetic recording medium) (not shown)
A still video signal recorded with M modulation (hereinafter referred to as RF
After the signal is read by the magnetic head 10, it is applied to the preamplifier l1. Regenerative RF amplified by amplifier 11
The signal is applied to an equalizer I2 to compensate so that upper and lower sideband components are approximately equal, and is applied to a trap circuit I3. The trap circuit 13 is a Takagi pass filter circuit that removes the C-RF signal from the reproduced RF signal and passes the Y-RF signal. The Y-RF signal output from the trap circuit l3 has its amplitude limited by a limiter l4, and then is applied to the FMiM modulation circuit l5. The luminance signal Y obtained by being demodulated by the demodulation circuit l5 is .
The signal is applied to the low-pass filter 1B.

The low-pass a overfilter te is for removing a portion of the carrier wave of FM modulation, and its cutoff frequency is approximately 6 MHz so that the high frequency component of the high band luminance signal Y can be sufficiently passed through. is set to . The demodulated luminance signal Y output from the low-pass filter 16 is applied to a de-emphasis circuit 17 and an integrator l9, respectively.

This luminance signal Y has the pre-emphasized Takagi frequency component suppressed by the de-emphasis circuit l7, and is output as a reproduced luminance signal on one side, and is given to the sync separation circuit i8 on the other hand. The synchronization separation circuit l8 converts the luminance signal Y into a vertical synchronization signal V or syn, a horizontal synchronization signal H, or both.
c Provided to the pull-hold circuit 20.

The integrator 19 is also a type of de-emphasis circuit. Since the de-emphasis circuit 17 is generally connected via a coupling capacitor, the DC component is removed, and the output of the circuit 17 does not accurately represent the level after FM demodulation. The integrator 19 integrates the level of the video signal after FM demodulation, including the DC component, so that its output level correctly represents the modulation frequency of the FM modulated video signal. In addition, the Takagi component, which is emphasized by pre-emphasis before video floppy recording, is suppressed. The synchronizing signal component sampled by the sample-and-hold circuit 20 at the next stage is waveform-shaped into the correct form.

FIG. 2 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 5 MHz, and the white peak frequency is 7.5 MHz. Let VN be the output voltage level of the demodulation circuit 15 with respect to the sync chip frequency. Also, the sync chip frequency of the high band recording method is 7
．． 7 MHz, and the white peak frequency is 9.7 MHz. The output level of the sync chip frequency demodulation circuit 15 is assumed to be Vn.

In this example, it corresponds to the sync chip frequency in the demodulated luminance signal. The output level vN or V is being detected. Further, a base level Vs between VN and Vo is set in advance. Then, by comparing the detected V or Vu with the reference level v8, it is determined whether the recording method is normal band or high band.

In Fig. 1, the horizontal synchronization signal H is output from the synchronization separation circuit l8.
is applied to the sample-and-hold circuit 20 and synced. The demodulated luminance signal Y is input to the sample and hold circuit 20 as described above. The sample hold circuit 20 controls the timing of the horizontal synchronization signal H manually.
Detect and hold the sync chip level sync (V or vH).

A signal N representing the sinking chip level V or Vo detected by the sample-and-hold circuit 20 is applied to the positive input terminal of the comparator 2l. This comparator 2
The above-mentioned reference level V8 is applied to the negative human power terminal of I. Therefore, in the normal band, vN × Vs
Therefore, the comparator 2l outputs an L level signal, and since VH>vs in the high band, the comparator 2l outputs an H level signal. The output signal of the comparator 2l becomes a high band/normal band discrimination signal.

The sampling operation in the sample/hold circuit 20 may be performed only once or may be performed multiple times. Also 1v
This may be performed every time the period of 1 has elapsed, or it may be performed only once in the reproduction of one track.

In the above embodiment, the horizontal synchronizing signal H is given to the sample-and-hold circuit 20, and the sync chip synchronizes at the timing of this horizontal sync signal H.
c Level V or Vn is detected and held. N Syn using vertical synchronization signal V or mixed synchronization signal C
c sync may be used. In that case, the entire period during which the vertical synchronization signal V or the hybrid synchronization signal C is output S)'
The integral value of ne will be detected and held by the sample-and-hold circuit 20.

FIG. 3 shows a specific example of the integrator 19 shown in FIG. 1. In this figure, the same components as those in the circuit shown in FIG. 1 are given the same reference numerals, and their explanation will be omitted.

The integrator i9 is composed of an amplifying transistor 23 for amplifying the demodulated luminance signal Y, an emitter follower circuit 24 whose base is connected to the collector of the amplifying transistor 23, a capacitor, and a resistor. Emitter
The brightness signal Y output from the follower circuit 24 is applied to the positive input terminal of the comparator 2I via the switching circuit 22, thereby distinguishing between high band recording and normal band recording.

FIG. 4 shows another embodiment.

In the circuit shown in FIG. 4, the luminance signal Y demodulated by the FM demodulation circuit l5 is applied to the integrator l9 for DC detection, and then directly inputted to the comparator 2l.
Sample and hold circuit 20 is not connected.

In this embodiment, the luminance signal Y is integrated by the integrator 19 over the entire period IV (V is the vertical scanning period). When integrated over the entire period of 1v in this way,
Since the integral values of high band recording and normal band recording are different, high band recording and normal band recording can be discriminated using a level intermediate between these integral values as a reference level.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a graph showing the characteristics of a demodulation circuit, and FIG. 3 is a diagram showing an example of the integrator circuit shown in the ml diagram. FIG. 4 is a block diagram showing another embodiment. Figure 5 (A). (B) is a diagram showing frequency allocation, where (A) shows normal band recording and (B) shows high band recording. 2I... Comparator, v8... Reference level generator. that's all

Claims (1)

[Claims] A device for determining whether a video signal read from a recording medium is one of two types of FM modulated video signals each having a different frequency band, the device demodulating the FM modulated video signal read from the recording medium. F
M demodulation circuit; integrating means for integrating the output signal of the FM demodulation circuit over a predetermined period; outputting a reference level having an intermediate level between the output levels of the two types of FM modulated video signals obtained from the integrating means; Determining the recording method of an FM modulated video signal, comprising: reference level setting means; and means for determining the type of recording method by comparing the level of the output signal of the integrating means with the reference level of the reference level setting means. device to do.