JPH035963A - Fm video signal reproducing device - Google Patents

Abstract

PURPOSE:To prevent a disturbance of a picture caused at the time of changing a circuit part by muting a regenerative video signal to be outputted from a reproducing circuit during the time required at least for the changeover when the circuit part in the reproducing circuit is changed in accordance with a recording system. CONSTITUTION:A recording system of an RF signal is discriminated by a high band / normal band discriminating circuit 30, and a high band / normal band discriminating signal S for showing this recording system is given to a changeover circuit 20 and a CPU 25. An amplifier 23 is controlled by the CPU 25 based on the high band / normal band discriminating signal in order to mute the output of a video signal during the time corresponding to the time required for changing the changeover circuit 20. That is, when the amplifier 23 is given a control signal from the CPU 25, its amplification degree is controlled to suppress a level of the video signal down to a pedestal level, and a synchronizing signal in the video signal is outputted as it is. By this method, the disturbance of the picture during the changeover is never generated.

Description

[Detailed Description of the Invention] Summary of the Invention Determining which of a plurality of recording methods in which a video signal read from a recording medium has been FM modulated and recorded using carrier waves of different frequencies, When it is necessary to switch circuit parts of the reproduction circuit according to the determination result, the reproduction video signal output from the reproduction circuit is muted at least during the time required for switching.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for reading and reproducing an FM modulated video signal recorded on a recording medium, such as a still video signal reproducing device.

Conventional technology and its problems Recording methods for recording still video signals on high-density magnetic floppy disks (video floppies) using electronic still cameras (still/video e-cameras) and other recording devices include the normal band recording method. There is a high band 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 a luminance signal Y (this FM modulated wave is abbreviated as a Y-RF multiplied signal). Two color difference signals R-Y and B-Y have a frequency of 1.2 MHz, respectively. 1.3M
FM modulates the Hz carrier wave and converts these FM modulated waves into C-
These Y-RF and C-RF multiplied signals are mixed and recorded on a track of a video floppy. These Y-RF multiplied signal C-RF multiplied signal frequency allocations are shown in FIG. 10(A). Y-R
F times signal sync chip (synchronization tip) frequency is 6M
Hz, white peak frequency is 7.5
MHz, and the frequency deviation is 1.5 MHz.

In a high-band recording method for recording a high-resolution still video signal, the center frequency of a carrier wave for FM modulation of the luminance signal Y is set to 9 MHz. Figure 1O (
As shown in B), the Y-RF multiplied signal sync chip frequency of the high band recording method is 7.7 MHz, the white peak frequency is 9.7 MHz, and the frequency deviation is 2.
It is MHz. 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.

Further, the discrimination circuit automatically discriminates the recording method of the still video signal, and the dedicated circuit portion is switched in accordance with the result of this discrimination.

However, since there is a potential difference between the normal band reproduced video signal and the high band reproduced video signal after demodulation, when the dedicated circuit section is switched, one image may be distorted during the time required for the switching. may occur,
This makes the image look unsightly.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION An object of the present invention is to provide an FM modulated video signal reproducing device that can prevent image disturbances that occur when switching the recording method of an FM modulated video signal.

Structure and Effects of the Invention The present invention is an apparatus capable of reproducing video signals recorded on a recording medium using any of a plurality of recording methods in which video signals are FM modulated using carrier waves of different frequencies.
a read head for reading the FM modulated video signal from the recording medium;
a determining means for determining by which recording method the FM modulated video signal read by the reading head has been FM modulated;
It outputs a predetermined reproduced video signal by applying predetermined processing including demodulation to the M-modulated video signal, and has a switchable circuit section for each recording method, and this circuit section is configured as described above. When it is necessary to switch the reproducing circuit which is switched and controlled according to the determination result by the discriminating means and the circuit part in the reproducing circuit according to the discriminating result by the discriminating means, the above-mentioned The present invention is characterized in that it includes means for muting the reproduced video signal output from the reproduction circuit.

According to this invention, when it is necessary to switch circuit parts within the playback circuit according to the recording method, the playback video signal output from the playback circuit is muted at least during the time required for switching.

No image disturbance occurs when circuit parts are switched, and unsightly screen displays are eliminated.

An embodiment in which the present invention is applied to a device capable of reproducing both the above-mentioned normal band recording and high band recording of still video signals will be described in detail below. Needless to say, the present invention can also be applied to an apparatus capable of reproducing both normal band recording and high band recording of recorded movie video signals.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a block diagram showing a reproducing apparatus for still video signals recorded on a video floppy, particularly a reproducing circuit for luminance signals.

Video floppy (magnetic recording medium) (path shown)
A still video signal recorded with M modulation (hereinafter referred to as RF
The multiplied signal) is read by the magnetic head 10 and then applied to the preamplifier 11. Regenerative RF amplified by amplifier 11
The signal is applied to an equalizer 12 to compensate so that upper and lower sideband components are approximately equal, and is applied to a 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 . The luminance signal Y obtained by being demodulated by the demodulation circuit 15 is passed through a first low-pass filter 16 . Second low pass filter 1
7 and a high band/normal band discrimination circuit 30, which will be described later.

Both the first low-pass filter 1B and the second low-pass filter 17 are for removing carrier wave components of FM modulation. The first low-pass filter 1B is for the normal band recording method, and its cutoff frequency is approximately 4.5 MHz, which corresponds to the frequency bandwidth of the baseband signal for normal band recording. Reference numeral 17 is for the high band recording method, and the cutoff frequency thereof is set to approximately 6 MHz, which corresponds to the frequency bandwidth of the baseband signal of the high band recording.

The normal band reproduction signal from which the carrier component has been removed by passing through the first low-pass filter 1B is applied to the a terminal of the switching circuit 20. Second low pass filter 1
The high band reproduction signal from which the carrier component has been removed by passing through the attenuator 18 is supplied to the attenuator 18 .

The FM demodulation circuit generates an output voltage that is approximately linear with respect to the frequency of the input signal. Therefore, the amplitude of a high band reproduction signal with a wide one frequency deviation is generally larger than that of a normal band. Attenuator 18 is R
This method corrects this amplitude difference in the reproduced signal that occurs in the F-fold signal demodulation process, and attenuates the amplitude of the high band reproduced signal to be approximately equal to the amplitude of the normal band reproduced signal. As a result, the amplitude of the high band reproduction signal applied to the b terminal of the switching circuit 20 becomes almost the same as the amplitude of the normal band reproduction signal applied to the a terminal.

The high band/normal band discrimination circuit 30 discriminates the RF double signal recording method, and a high band/normal band discrimination signal representing the recording method is given to the switching circuit 20 and the CPU 25. Details of the high band/normal band discrimination circuit 30 will be described later. Based on the high band/normal band discrimination signal given from the high band/normal band discrimination circuit 30, the CPU 25
The amplifier 2, which will be described later, mutes the output of the video signal for a time corresponding to the time required for switching the switching circuit 20.
Control 3.

The switching circuit 20 switches between the a terminal and the b terminal based on the high band/normal band discrimination signal.

The switching circuit 20 determines that the high band/normal band discrimination signal indicates normal band recording.

The a terminal side becomes conductive so that the first low-pass filter 1B outputs a luminance signal from which the carrier component has been appropriately removed. Furthermore, when the high band/normal band discrimination signal indicates high band recording, the switching circuit 20 properly removes the carrier wave component by the second low pass filter 17, and changes the amplitude of the high band reproduced signal to the normal band. The b terminal side is brought into conduction so that the output signal from the attenuator 18, which is made approximately equal to the amplitude of the reproduced signal, is output as a luminance signal.

After the high frequency components of the signals selected by the switching circuit 20 are suppressed by the de-emphasis circuit 22, one signal is outputted as a luminance signal Y via the amplifier 23, and the other signal is provided to the sync separation circuit 24.

The synchronization separation port 24 extracts a synchronization signal from the luminance signal Y and supplies it to the high band/normal band discrimination circuit 30.
Used for high band/normal band discrimination processing.

A control signal is given to the amplifier 23 from the CPU 25, whereby the reproduced video signal is muted during the time required for the switching process of the switching circuit 20. That is, when this amplifier 23 receives a control signal from the CPU 25, its amplification degree is controlled so as to suppress the level of the video signal to the pedestal level. Needless to say, the synchronization signal in the video signal is output as is. This prevents image distortion from occurring during switching.

Next, high band/normal band discrimination processing by the high band/normal band discrimination circuit 30 will be described.

A detailed block diagram of the high band/normal band discrimination circuit 30 is shown in FIG.

Referring to FIG. 2, the luminance signal Y demodulated by the FM demodulation circuit 15 is output to
2 are given respectively.

FIG. 4 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 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 aN2. 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 respectively expressed as g) 13'.
Let gH2' gHl.

On the other hand, as shown in Fig. 5, the frequency difference a between the white peak and the sink urn chip, the frequency difference a between the white peak and the pedestal level, and the frequency difference between the pedestal level and the sink urn chip. When C is 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:c=1:0.7
14: It is determined to be 0.28B.

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 aH) is 2.0M.
Since it is Hz, it is aN/aH-3/4. Assuming that the characteristics of the demodulation circuit 15 are linear, (g −g
) / (gHl-aN3) ””NI N3 3/4.

Pedestal φ level and sync in normal band
Let C be the frequency difference with the chip, and CH be the frequency difference between the pedestal level and the sync chip in the high band. As explained with reference to FIG. 5, since c/a is constant regardless of the recording method, CN/a N
” CH/a H-c/a.a N/a
Because it is n-3/4.

c N/c n -3/4. Expressing this relationship in terms of the output voltage difference of the demodulation circuit 15, cN/cH-(a
N2-aN3) / (aN2-aN3) = 3/
It becomes 4.

In this high band/normal band discrimination circuit 3o, (g
N2- g N3) or (g N2 g N3)
is being detected. Also, ( g N2- g N3) and (
A reference level VR between (g N2 g N3) is set in advance.

Then, the detected (g N2- aN3) or (g
H2gHa) by comparing it to the reference level vR.

Determines whether the recording method is normal band or high band.

FIG. 3 shows the relationship between the synchronization signal portion of the demodulated luminance signal Y and sample pulses SPI and SF3 for sampling the pedestal level and sync-tip level from this synchronization signal portion.

In FIG. 2, based on the synchronization signal provided from the synchronization separation circuit 24, the timing generation circuit 35 generates the above-mentioned sample pulse SP1. SP2 is generated and applied to sample and hold circuits 31 and 82, respectively. As described above, the demodulated luminance signal Y is input to each of the sample and hold circuits 31 and 32. Sample/hold circuit is sample pulse SP
At the timing of I, the pedestal level (g or gH
2) Detect and hold. The sample 2 hold circuit 32 detects the sync chip level (gN8 or gH) at the timing of the sample conflict pulse SP2.
a) Detect and hold.

The pedestal signal detected by the sample and hold circuit 31
A signal representing the level is sent to the differential amplifier 33 via the resistor R1.
A signal representing the sync tip level detected by the sample and hold circuit 32 is applied to the negative input terminal of the differential amplifier 33 via a resistor R2. The differential amplifier 33 has a feedback loop in which the output signal is fed back to the positive input terminal via the resistor R4, and the negative input terminal is grounded via the resistor R3. By this differential amplifier 33, the pedestal
The level difference between the level and the sync tip level (g
-g ) or (g N2 g N3) is detected.

The output of the differential amplifier 33 is applied to the positive input terminal of the comparator 34. The reference level VR is applied to the negative input terminal of the comparator 34. therefore.

When it is a normal band, (gN2- gN3)<vR
Therefore, when the L level signal from the comparator 34 is in the noi band, N2 where (g − g )>VR
From ttl, the comparator 34 outputs an H level signal. The output signal of the comparator 34 becomes a high band/normal band discrimination signal.

As described above, switching control of the switching circuit 20 and muting of the amplifier 23 are performed by the CPU 25 based on this high band/normal band discrimination signal.

FIG. 6 shows another embodiment. In Figure 6, the first
Components that are the same as the circuits shown in the figures are given the same reference numerals and their explanations will be omitted.

The luminance signal Y obtained by demodulation by the demodulation circuit 15 is given to a low-pass filter 19 and a high band/normal band discrimination circuit 30.

The low-pass filter 19 also has the above-mentioned first. Like the second low-pass filters 16 and 17, it is for removing the carrier wave component of FM modulation, and its cutoff frequency is
The frequency is set to about 6 MHz so that the high frequency component of the high band luminance signal Y can be sufficiently passed through. The demodulated luminance signal Y output from the low-pass filter 19 is given to an automatic gain control amplifier circuit 21.

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 21 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 automatic gain control amplifier circuit 21 is controlled by the output signal of a differential amplifier 33 included in a high band/normal band discrimination circuit 30 shown in FIG. That is,
When the output signal level of the differential amplifier 33 is high (high band), the gain of the automatic gain control amplifier circuit 21 becomes a relatively small value, and conversely, when the output signal level of the differential amplifier 33 is small ( (normal band), the gain of the automatic gain control amplifier circuit 21 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 21 has its high frequency components suppressed by the de-emphasis circuit 22, and then one is outputted as a luminance signal Y via the amplifier 23, and the other is outputted to the sync separation circuit 19. What is given is as described above.

The sampling operation (generation of sample pulses SP1 and SP2) in the sample-and-hold circuits 31 and 32 is performed in the portion of the hybrid synchronization signal, and may be performed only once or multiple times. Further, it may be performed every time a period of 1v has elapsed, or it may be performed only once in the reproduction of one track.

The embodiment shown in FIG. 6 has an advantage in that one circuit can be simplified because only the gain of the automatic gain control amplifier circuit 21 is switched depending on the recording method determination result.

FIG. 7 shows a modification of the high band/normal band discrimination circuit 30 (this circuit is particularly designated by the reference numeral 30A). In addition, Fig. 8 shows the main operations of the circuit shown in Fig. 7, especially the operations during the vertical retrace period, and Fig. 9 shows the time axis of the time chart shown in Fig. 8 by extending it further. It is shown in detail.

The luminance signal Y demodulated by the FM demodulation circuit 15 is sent to the amplifier 41
is amplified. Regenerative RF amplified by amplifier 41
The signal is provided to a high pass filter 42.

The recording method discrimination process is performed in a very short period (period T 2 to be described later) within the period in which the vertical synchronizing signal appears. During this period, the reproduced RF signal includes a Y-RF multiplied signal sync chip frequency component, a C-RF multiplied signal center frequency component, and a synchronization signal component. The high-pass filter 42 passes only the Y-RF multiplied signal sync chip frequency component, and its cutoff frequency is set to about 1.5 MHz, for example.

The signal that has passed through the high-pass filter 42 is applied to a Schmitt inverter 43, where it is level-discriminated using a zero-level threshold and shaped into a pulse signal (or square wave signal). This pulse signal is input to the counter 44. As will be described later, the counter 44 operates only during the period T2 to count the input pulse signals. The input pulse signal (normal band-sync chip component, high-band sync chip component) of the counter 44 and the output signal of the counter 44 during this period T2 are shown in FIG.

As shown in FIG. 1, the reproduced RF signal demodulated by the FM demodulation circuit 15 is input to the synchronization separation circuit 24 via the de-emphasis circuit 22. The synchronization separation circuit 24 outputs a vertical synchronization signal V and a horizontal synchronization signal H3aneync. The signal necessary for the operation of the high band/normal band discrimination circuit 30A shown in FIG. 7 is the vertical synchronization signal V.
Therefore, only the vertical synchronizing signal yne separated by two is the first monostable multivibrator 4 Byyn.
Enter c.

FIG. 8 shows a composite synchronization signal C extracted from the demodulated video signal. The vertical synchronizing pulse part of this hybrid synchronizing signal C has a width of 3H, and in order to prevent the horizontal synchronizing signal from disappearing during that time, this pulse part is 0.07H wide and is divided into six pulses every 0.43H. It is a separation. This (1,07H width pulse portion will be referred to as a delimiter pulse portion a).

There are various types of synchronization separation circuits 24, but in this high band/normal band discrimination circuit 30A, the circuit 24 detects a vertical synchronization signal V delayed by approximately IH from the vertical yne 5th period pulse portion in the hybrid synchronization signal C.
This outputs the following. This vertical synchronization signal ync signal V is given to the first monostable multivibrator ync (MMI) 4B. The output signal of the monostable multivibrator 4B rises in synchronization with the rising edge of the vertical synchronizing signal V 1 and is held at the H level for a predetermined time T1 (16 μs in this embodiment). This output signal is applied to the clear terminal of the counter 44 and the second monostable multi-by-break (MM2) 47.

The second monostable multivibrator 47 rises in synchronization with the fall of the output of the first monostable multivibrator 46, and then for a predetermined time T2 (3.5 μs in this embodiment).
This output signal is applied to the enable terminal of the counter 44. therefore,
The counter 44 will open during this period T2.

The period T2 during which the counter 44 operates is approximately at the center of the vertical synchronizing pulse portion of the hybrid synchronizing signal C, preferably between the second and third delimiter pulse portions a, or as shown in FIG. It is set to be between the third and fourth delimiter pulse portions a.

This is because although the sync chip frequency component signal input to the counter 44 may be disturbed at the edges of the vertical synchronizing pulse portion, this disturbance is considered to be less near the center of the vertical synchronizing pulse portion. Further, this period T2 is set to be located approximately at the center of the adjacent delimiter pulse portions a. This is also to perform the total a1 operation of the sync chip frequency in a portion where signal disturbance is as small as possible.

As shown by the chain line in FIG. 8, when a synchronization separation circuit is used that generates a vertical synchronization signal V that rises with almost no delay from the vertical synchronization pulse portion of the hybrid synchronization signal Csync, the first monostable The multivibrator 46 will be one that outputs 12 one-shot competition pulses for a period approximately IH longer than the period Ti.

The counter 44 is cleared by the output signal of the first monostable multivibrator 46, and then performs a counting operation in which the output of the monostable multivibrator 47 of node 2 is at H level, and is output from the Schmidt inverter 43. The frequency signal created by the sink chip is divided by 1/1G in this embodiment. As described above, the sync chip frequencies are different between normal band recording and high band recording, so even if frequency division is performed at the same ratio, the frequencies after frequency division will be different. In this embodiment, the counting operation period T2 of the counter 44 is set to 3.5 μs.1 As shown in FIG. The output of 44 becomes L level, and in the case of a 7.7 MHz signal, becomes H level and is held at that level. Therefore, it is possible to determine whether normal band recording or high band recording is being performed based on the level of the output signal of the counter 44 at the time when one period T2 has elapsed.

The output signal of the counter 44 is given to a low pass filter 45. The output signal of the low-pass filter 45 is given to the above-mentioned switching circuit 20 and CPU 25 as a high band/normal band discrimination signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention. Figure 2 is a block diagram showing the high band/normal band discrimination circuit, Figure 3 is a time chart showing the relationship between the luminance signal synchronization signal and sample pulse, and Figure 4 is a graph showing the characteristics of the FM demodulation circuit. . FIG. 5 is a waveform diagram showing a luminance signal, and FIG. 6 is a block diagram showing another embodiment. FIG. 7 is a block diagram showing a modification of the high band/normal band discrimination circuit, FIG. 8 is a time chart showing the main operations of the circuit shown in FIG. 7, and FIG. 9 is a time chart showing the main operations of the circuit shown in FIG. The time of the chart is extended to show details. FIGS. 10(A) and 10(B) are diagrams showing frequency allocation, where (A) shows normal band recording and (B) shows high band recording, respectively. 1B, 17.19...Low pass filter. 20...Switching circuit. 21...Automatic gain control amplifier circuit. 23...Amplifier. 25...CPU. 30, 3OA... High band/normal band discrimination circuit. that's all

Claims (1)

[Claims] A device capable of reproducing video signals recorded on a recording medium by any of a plurality of recording methods in which video signals are FM modulated using carrier waves of different frequencies, a reading head for reading from the reading head; a determining means for determining which recording method the FM modulated video signal read by the reading head has been FM-modulated; and demodulating for the FM modulated video signal read by the reading head. It outputs a predetermined reproduced video signal by applying predetermined processing including When it is necessary to switch the controlled reproduction circuit and the circuit portion in the reproduction circuit according to the determination result by the discrimination means, a reproduced video signal output from the reproduction circuit at least for the time required for switching. A reproducing device for an FM modulated video signal, comprising means for muting the FM modulated video signal.