JPH0453099Y2 - - Google Patents

Description

[Detailed Description of the Invention] (A) Field of Industrial Application The present invention relates to a reproducing device for a magnetic disk in which one field of video signals is recorded on each annular track, and particularly to a reproducing device for an electronic still camera.

(b) Conventional technology Regarding electronic still cameras, for example, Nikkei Electronics, a magazine created by Nikkei McGraw-Hill,
``Recording 25 still images on a 47mm diameter floppy disk...
...” is shown. The magnetic disk used in this electronic still camera is called a video floppy.

One field of video signals is recorded on each of the annular tracks provided on the video floppy. Recording by this electronic still camera includes field recording, which is recorded on one track, and frame recording, which is recorded on two tracks.

By the way, it is possible to use this video floppy for purposes other than recording video signals. For example, writing an audio compressed signal (referred to as audio recording). It is also conceivable to write digital signals (referred to as data recording) in the same way as a normal floppy disk.

When a video floppy on which such various recordings have been made is played back by an electronic still camera playback device, a noise signal is displayed on the display device (monitor television) except when the video signal is played back.

Therefore, it is conceivable to mute the output of the video signal when the electronic still camera player cannot reproduce a normal video signal. However, in order to perform mute, a video presence/absence determination circuit is required to determine the presence or absence of a video signal.

This video presence/absence determination circuit detects the periodicity of the horizontal synchronization signal. An example of this will be explained below. First, the horizontal synchronization signal is input to the horizontal AFC circuit. Then, this horizontal AFC circuit outputs a signal (hereinafter referred to as a horizontal AFC signal) synchronized with the horizontal synchronization signal. The phase relationship between the horizontal AFC signal and the horizontal synchronization signal is constant if the video signal is normal. In other words, by comparing this horizontal AFC signal and the horizontal synchronization signal, it is possible to determine the presence or absence of a video signal.

The above video signal presence/absence determination circuit naturally requires continuity (constant phase) of the horizontal synchronizing signal. In an electronic still camera, when a frame-recorded signal is played back, the horizontal synchronization signal is continuous. However, when reproducing a field-recorded signal, a discontinuous point occurs in the horizontal synchronizing signal every time one field is reproduced (every one rotation).
). This discontinuity point causes the video signal presence/absence determination circuit to malfunction.

By the way, JP-A No. 57-141183 and JP-A No. 46-
0.5H (H is horizontal scanning period) as shown in No. 16178
It is possible to prevent the occurrence of the above-mentioned discontinuity point by using a delay line of .

Therefore, when playing back what has been recorded in the field (hereinafter referred to as field playback), it is necessary to prevent the occurrence of discontinuities using a 0.5H delay line before making a decision using the video signal decision circuit.

(c) Problems that the invention attempts to solve However, the monitor TV has a horizontal AFC circuit (this horizontal AFC circuit is built into the monitor TV, and the
It is separate from the AFC circuit. ) with a short pull-in time, the horizontal AFC circuit will synchronize with the horizontal synchronization signal shifted by 0.5H during field playback, and a normal image will be displayed on the monitor TV during the vertical retrace period. If you do this,
A 0.5H delay line is not particularly necessary.

Also, during field reproduction, after extracting the horizontal synchronization signal within the vertical retrace period including the discontinuity point, a pseudo horizontal synchronization signal without the discontinuity point is created,
Re-insert this and monitor TV horizontal AFC
It is also possible to prevent circuit disturbances. In this way, a 0.5H delay line is not particularly necessary.

As mentioned above, when attempting to determine the presence or absence of a video signal in an electronic still camera that does not particularly require a 0.5H delay line, an expensive delay line is required for this determination.

The present invention has been made in view of the above points, and provides a video signal presence/absence determination circuit that does not require a 0.5H delay line.

(d) Structure of the invention The invention detects the starting edge of the video signal (discontinuous point of the horizontal synchronization signal), and from this point on, disables the determination circuit output during the pull-in period of the horizontal AFC circuit (horizontal synchronization oscillation circuit). This is a video presence/absence determination circuit including an invalid circuit.

(E) Effect Since the present invention has the above configuration, the horizontal AFC
During the pull-in period until the circuit (horizontal synchronization oscillation circuit) synchronizes with the horizontal synchronization signal, the determination circuit is disabled to prevent malfunction.

(f) Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 and 2. The electronic still camera playback device shown in FIG. 1 will be explained. 10 is a video floppy,
An FM modulated video signal is recorded. or,
The video floppy rotates at 3600 rpm. 12,
Reference numeral 12 denotes magnetic heads, each of which reproduces one track of signals. Reference numeral 14 denotes a changeover switch, which outputs a reproduction signal from one head to a subsequent circuit during field reproduction. Also, this changeover switch 14
During frame reproduction, the signals from the heads 12, 12 are switched and selectively output for each field (for each rotation). 16 is an amplifier. A video signal processing circuit 18 demodulates the reproduced FM video signal, determines whether the recorded video signal is field recording or frame recording, and controls the changeover switch 14. In the video signal processing circuit 18, in the case of field reproduction, a 0.5H delay circuit or the like is used to eliminate discontinuities in the horizontal synchronizing signal. 2
0 is a mute circuit that mutes the video signal from the video signal processing circuit 18.

22 is a synchronization separation circuit (horizontal synchronization separation circuit), which extracts a synchronization signal (horizontal synchronization signal) from the video signal from the video signal processing circuit 18. Note that the video signal input to the synchronization separation circuit 22 is a video signal obtained by demodulating the FM video signal from the amplifier 16, and is not a video signal in which discontinuities are eliminated using a 0.5H delay circuit. 24 is a horizontal AFC circuit (horizontal synchronous oscillation circuit), and synchronous separation circuit 22
Outputs a horizontal AFC signal synchronized with the horizontal synchronization signal from the Note that the pull-in period of this horizontal AFC circuit 24 is 20H. That is, the phases of the horizontal synchronizing signal and the horizontal AFC signal match 20H after the discontinuous point of the horizontal synchronizing signal is input to the horizontal AFC circuit 24 during field reproduction.

26 is a coincidence signal generation circuit, which is a horizontal AFC
It works to detect the degree of phase matching between the signal and the horizontal synchronization signal. Each part of this coincidence signal generation circuit 26 will be explained. 28 is a short pulse conversion circuit that converts the horizontal AFC signal into a short pulse signal. 30 is an AND gate that detects the phase difference between the output of the short pulse conversion circuit 28 and the horizontal synchronization signal. The short pulse conversion circuit 28 shortens the pulse width of the horizontal AFC signal and outputs the signal only when it exactly matches the horizontal synchronizing signal. In addition, and gate 30
has one more input, which will be explained later. 32 is a pulse width conversion circuit, which is constituted by a retriggerable monomulti which outputs a 1H width pulse every time a rising signal is input. 3
4 is an integrating circuit with a time constant of 1/60 seconds or more. When the horizontal AFC signal and the horizontal synchronization signal inputted to the coincidence signal generation circuit 26 are in phase, the AND gate 30 outputs a pulse every 1H. Therefore, the signal from the pulse width conversion circuit 32 is Always at a high level. The signal from the integrating circuit 34 is also at high level. In other words, the output voltage of the coincidence degree signal generation circuit 26 increases or decreases depending on the degree of coincidence between the horizontal AFC signal and the horizontal synchronization signal.

Reference numeral 36 is a gate pulse generation circuit (invalidation circuit) showing the feature of the present invention. This gate pulse generation circuit 36 detects a discontinuous point in the horizontal synchronization signal (recording start edge of the video signal), and the horizontal AFC circuit 24
During 20H of synchronizing with the horizontal synchronization signal shifted by 0.5H,
This is to stop the operation of the coincidence degree signal generation circuit 26.

This gate pulse generation circuit 36 uses the fact that the discontinuity point during field reproduction is 7H±2H before the start point of the vertical synchronization signal of the video signal to generate a gate that controls the operation of the coincidence degree signal generation circuit 26. Creating a pulse.

Each part of the gate pulse generation circuit 36 will be explained with reference to the waveform diagram in FIG. A in FIG. 2 shows the relationship between the discontinuous point of the horizontal synchronizing signal and the vertical synchronizing signal (V.SYNC) during field reproduction, and this is defined by the electronic still camera standard.
In Figure 1, 38 is an integration circuit, 40 is a hysteresis comparator, and these 38 and 40 take out the vertical synchronization signal (V.SYNC) (second
(See Figure B). 42 and 44 are monostable multivibrators, each outputting a signal CD in FIG. 2. In other words, during field reproduction, the gate pulse generation circuit 36 generates a low level signal during the pull-in period shown in FIG. Output. Therefore, during this period, the output of the AND gate 30 is forced to a low level, and the coincidence signal generation circuit 26 becomes inactive.

46 is a comparison circuit, and the coincidence signal generation circuit 2
6 and a reference voltage (Vf) to determine the presence or absence of a video signal and output a mute signal.

The operation of the electronic still camera playback device during field playback will be described. video floppy 10
It rotates at 3600rpm. One of the video heads 12 reproduces the FM video signal from the video floppy 10. The reproduced FM video signal is switched to switch 1.
4 and the video signal processing circuit 18 via the amplifier 16
is input. The video signal processing circuit 18 demodulates the FM video signal and outputs it to the sync separation circuit 22, and also outputs the video signal to the mute circuit 20 after eliminating discontinuities in the horizontal sync signal using a 0.5H delay line. Output.

The synchronization separation circuit 22 is a horizontal synchronization signal (H.SYNC)
Take out. This horizontal synchronization signal is input to the horizontal AFC circuit 24. Then, the coincidence degree signal generation circuit 26 compares the phases of the horizontal AFC signal and the horizontal synchronization signal using an AND circuit 30, thereby outputting a signal related to the presence or absence of the video signal. However, the horizontal
From the discontinuity point of the horizontal synchronization signal, the AFC circuit 24
Oscillation is disturbed during the pull-in period (20H). Therefore, the phase of the horizontal AFC signal and the horizontal synchronization signal input to the coincidence degree signal generation circuit 26 are different for 20H from the discontinuity point of the horizontal synchronization signal. Therefore, the gate pulse generation circuit 36 generates a gate pulse signal that keeps the output of the AND circuit 30 at a low level for 20H from the approximately discontinuous point.

The creation of this gate pulse signal will be explained. First, the integrating circuit 38 extracts a vertical synchronizing signal. Thereafter, it is shaped by a hysteresis comparator 40 (see FIG. 2B). Thereafter, the monostable multivibrators 42 and 44 output the signals CD in FIG. 2, respectively. The signal shown in FIG. 2D is a gate pulse signal, and remains at a low level for a period of approximately 20H from the point of discontinuity in the horizontal synchronizing signal. This gate pulse signal causes the AND circuit 30 to output a low level signal until the horizontal AFC signal from the horizontal AFC circuit 32 and the horizontal synchronizing signal match in phase. Therefore, it is possible to prevent the output of the AND circuit 30 from becoming unstable until the phases match.

In the case of frame reproduction, the changeover switch 14 is switched every rotation (one field), and the horizontal synchronization signal is continuous. However, this electronic still camera playback device operates in the same way during frame playback as it does during field playback. That is, the gate pulse generation circuit 36 is activated to keep the output of the AND circuit 30 at a low level for 20H from 5H before the start of the vertical synchronization signal. Therefore, the output voltage value from the integrating circuit 34 is the same as that at the time of field reproduction.

Note that the horizontal synchronization signal and vertical synchronization signal are not detected accurately and the horizontal AFC is
The possibility that the signal and the output of the synchronization separation circuit 22 are in phase becomes smaller, and the output level of the integration circuit 34 decreases.

In this embodiment, the start edge of the video signal was detected from the vertical synchronization signal, but for example, if the video floppy 1
The starting end of the video signal may be detected using the PG detection signal obtained by detecting the PG yoke provided at the PG yoke.

Further, in this embodiment, the output of the AND circuit is set to a low level during the pull-in period (during 20H), but the value of the integrating circuit 34 may be held, for example, during this pull-in period.

Furthermore, in this embodiment, when there is no video signal, the video signal is simply muted. However, the color displayed on the monitor TV may be changed depending on the situation. For example, by detecting the playback envelope of a video floppy, it is possible to detect whether it is unrecorded or recorded. Therefore, by combining this detection output with the output of the video presence/absence determination circuit of the present application, three modes can be determined: "no recording", "audio storage or data recording", and "video recording". Using this, in the case of "no record",
For example, set the monitor TV to display red,
Yellow may be displayed when "audio or data recording" is being performed.

(g) Effects of the invention As described above, the invention is useful because it can determine the presence or absence of a video signal during field playback, regardless of the 0.5H delay line.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing the waveforms of each part. 10...Video floppy (magnetic disk),
22... Synchronization separation circuit (horizontal synchronization separation circuit), 2
4...Horizontal AFC circuit (horizontal synchronous oscillation circuit), 26
... Matching degree signal generation circuit (judgment circuit), 36 ...
Gate pulse generation circuit (invalid circuit).

Claims (1)

[Scope of Claim for Utility Model Registration] In a magnetic disk playback device in which one field of video signals is recorded on each of a plurality of annular tracks, a horizontal synchronization signal separation circuit for extracting a horizontal synchronization signal from a playback video signal; a horizontal synchronization oscillation circuit that outputs a signal synchronized with a horizontal synchronization signal; a determination circuit that compares the output of the horizontal synchronization oscillation circuit with the horizontal synchronization signal to determine the presence or absence of a video signal; and a starting end of the video signal of the one field. detect,
A video presence/absence determination circuit comprising: an invalidation circuit that disables the determination circuit for a period corresponding to a pull-in period of the horizontal synchronization oscillation circuit from this start end.