JPH0773355B2 - Magnetic recording / reproducing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video tape recorder or the like that converts a video signal into a digital signal by an analog / digital (A / D) converter and then performs digital signal processing using an image memory. The present invention relates to a magnetic recording / reproducing apparatus.

Conventional technology In recent years, due to the rapid development of semiconductor technology, it has become possible to realize large-scale digital circuits as LSIs and high-speed A / D converters and D / A converters that can operate at video rates. Digital signal processing is becoming a reality. Improvement of basic performance by digitization of TV receivers and video tape recorders (hereinafter abbreviated as VTRs), which are consumer video equipment, efficient connection with new media equipment, stable quality uniformity, reduction of parts count, service In addition to improving the efficiency of the system, the adoption of a digital memory and memory controller, which have been significantly increased in capacity and cost in recent years, has enabled various functional features such as screen stillness, parent-child screen (picture-in-picture), and multi-screen. Digital application equipment possessed has been developed (for example, magazine "TV Technology" 1986. VOL. 3
4.P.19).

A conventional magnetic recording / reproducing apparatus will be described below with reference to the drawings.

FIG. 2 shows main blocks of a conventional magnetic recording / reproducing apparatus. In FIG. 2, 1 is a magnetic tape, 2 is a magnetic head, 4 is a video signal processing circuit for recording and reproducing a video signal, 6 is a switching circuit, 7 is a video signal input end, 8 is a video signal output end, 9 is a motor drive / servo circuit for driving and controlling the VTR drive mechanism, 10 is a control microcomputer (hereinafter referred to as a control microcomputer), 11 is an operation unit, and 12 is an A / D.
Converter, 13 is an image memory, 14 is a D / A converter, 15 is a memory control circuit for controlling writing and reading addresses and timing of the image memory, 16 is a clock oscillation circuit, 17 is a sync separation circuit, 50 Is a digital processing unit.

The operation of the conventional magnetic recording / reproducing apparatus configured as described above will be described below.

First, the video signal input to the input terminal 7 is subjected to various signal processing for recording the video signal on the magnetic tape by the video signal processing circuit 4 via the switching circuit 6, for example, FM modulation, white clip, dark clip. Etc. are given. Since the recording process of this part is well known, detailed description thereof is omitted (for example, magazine "Home VTR Primer", Corona Publishing Co., PP151).
~ 183). After the recording process is performed as described above, the magnetic head 2 records on the magnetic tape 1. Further, the video signal input to the video signal processing circuit 4 is digitally processed by a digital processing unit 50 (details of which will be described later) after being subjected to auto gain control (AGC) in the video signal processing circuit 4 during recording. It is possible to output to the output end 8 after being processed.

When reproducing the video information recorded on the magnetic tape 1,
The video information recorded on the magnetic tape 1 is detected by the magnetic head 2 and then supplied to the video signal processing circuit 4, where the video signal is reproduced, for example, FM demodulated. Like the above-mentioned recording process, it is well known and its detailed description is omitted). The reproduced video signal (hereinafter, abbreviated as reproduced video signal) is supplied to the digital processing unit 50, and is subjected to the digital processing designated by the operation unit 11. The digital processing unit 50 converts the reproduced video signal, which is an analog signal, into
It is converted into a digital signal by the A / D converter 12 and written in the image memory 13. The memory control circuit 15 controls write addresses and read addresses of the image memory 13 and timings of writing and reading. With this memory control, processing such as stillness, reduction and enlargement of an image can be performed. For example, a one-field or one-frame still image can be realized by sequentially writing one-field or one-frame image data to each address in the image memory and then sequentially reading the image data at each address. Further, the reproduced video signal is subjected to synchronous separation in the synchronous separation circuit 17, and the output horizontal synchronizing signal is supplied to the memory control circuit 15 so that the image data is synchronized with the reproduced video signal in the image memory 13. To write to and read from,
Thereby, the memory address and the image data are associated with each other. The memory control circuit 15 can have several image data processing modes according to the memory control method of the memory control circuit 15. The mode designation is performed by the mode command selected by the operation unit 11. Is transmitted to the control microcomputer 10, and the memory control method of the memory control circuit 15 is designated from the control microcomputer 10. The control microcomputer 10 is configured to control a motor drive for driving and controlling the traveling mechanism of the VTR, a servo circuit 9 and a switching circuit 6 for switching a recording video signal according to a mode command from the operation unit 11.

In addition, the clock oscillator circuit 16 includes an A / D converter 12 and a D / A converter.
In addition to generating 14 sampling clocks, it serves as a reference clock for the memory control circuit 15 that controls the writing and reading timings of the image memory 13. The clock is a carrier color subcarrier included in the input video signal (hereinafter,
It is phase-locked to a burst signal) and uses a frequency three or four times the burst frequency.

Next, consider a case where the image data written in the image memory 13 is read out and recorded again at an arbitrary position on the magnetic tape 1. The image data read from the image memory 13 is converted into an analog video signal by the D / A converter 14, and then output to the output terminal 8 and supplied to the switching circuit 6. The switching circuit 6 is controlled by the control microcomputer 10. By switching the switching circuit 6 to the D / A converter 14 side (the switching circuit 6 in FIG. 2 is the lower side) by the control microcomputer 10, D /
The output signal of the A converter is guided to the video signal processing circuit 4, where it is subjected to recording processing and then recorded on the magnetic tape through the magnetic head 2.

As described above, the reproduced video signal can be digitally processed and then output from the output terminal 8, or the digitally processed video signal can be recorded again on the magnetic tape.

Problems to be Solved by the Invention However, with the above configuration, the image memory
The clock output of the clock generation circuit 16 is unstable when the image data written in 13 is to be recorded at an arbitrary position on the magnetic tape 1 (when the switching circuit 6 is connected to the D / A converter 14 side). As a result, the reading timing of the image memory 13 becomes unstable, and normal image data (video signal) cannot be recorded.

That is, as described above, the clock generation circuit 16 operates so as to output a clock phase-synchronized with the burst signal included in the output video signal of the video signal processing circuit 4,
The image data of the image memory 13 is read by this clock and converted into an analog video signal by the D / A converter 13. At this time, since the digital processing in the A / D converter 12, the image memory 13, and the D / A converter 14 requires a processing time, the D phase is different from the burst phase of the input video signal of the clock generation circuit 16. /
The burst phase of the output video signal of the A converter 14 causes a phase difference of only _A. Further, the output video signal of the D / A converter 14 is input to the clock generation circuit 16 again after being subjected to AGC in the video signal processing circuit 4 via the switching circuit 6 as described above. Actually, the video signal is delayed also in the switching circuit 6 and the video signal processing circuit 4, and if the burst phase difference between them is _B , then in the clock generation circuit 16, _A +
It operates to synchronize the phase again with the burst phase having a phase difference of _B. After all, in order to form a closed loop of the clock generation circuit 16 → A / D converter 12 → image memory 13 → D / A converter 14 → switching circuit 6 → video signal processing circuit 4 → clock generation circuit 14, in this closed loop Therefore, the phase of the burst signal cannot be synchronized, and the phase of the output clock of the clock generation circuit 16 falls into an unstable state. Therefore, the burst phase of the video signal output from the D / A converter 14 becomes unstable, and a video signal with uneven hue is recorded on the magnetic tape.

In view of the above problems, the present invention is a magnetic recording capable of generating a stable clock even when recording a video signal written in an image memory at an arbitrary position on a magnetic tape and recording a video signal without hue unevenness. A playback device is provided.

Means for Solving the Problems In order to solve the above problems, the magnetic recording / reproducing apparatus of the present invention is an A / D converter for converting an input video signal into a digital signal, and digitization by the A / D converter. An image memory for storing the video signal thus generated, a D / A converter for converting the digital signal read from the image memory into an analog video signal, and a clock pulse synchronized with the burst phase of the input video signal Any one of a first clock generator, a second clock generator that generates a free-running clock pulse separately from the clock generator, and outputs of the first clock generator and the second clock generator. A first switching circuit for selecting one of the two, and a memory control circuit for controlling the write and read addresses and timing of the image memory with reference to the output of the first switching circuit. A path, a video signal recording means for recording the image information written in the image memory in a fixed section of the magnetic tape, and the first switching circuit in the second switching circuit when recording on the magnetic tape. A control circuit for switching to the clock generator side is provided.

The present invention has the above-described configuration, and when the video signal stored in the image memory is recorded at an arbitrary position on the magnetic tape, the clock that oscillates by self-excitation without using the clock synchronized with the input burst signal. By reading the image data using the, it becomes possible to read the image data in a stable manner, and it is possible to record a video signal without hue unevenness.

Embodiment A magnetic recording / reproducing apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of essential parts of a video signal processing device according to an embodiment of the present invention. In FIG. 1, 1 is a magnetic tape, 2 is a magnetic head for recording and reproducing video signals,
4 is a video signal processing circuit, 6, 33 and 34 are switching circuits, 7 is a video signal input terminal, 8 is a video signal output terminal, 9 is a motor drive / servo circuit for driving and controlling the VTR traveling mechanism section, 10 is a control microcomputer , 11 is an operation unit, 12 is an A / D converter, 13 is an image memory, 14 is a D / A converter, 15 is a memory control circuit, 16 is a clock generation circuit 1, 17 is a sync separation circuit, and 31 is a clock generation circuit. The circuits 2 and 32 are horizontal synchronizing pulse generation circuits, and 51 is a digital processing unit.

The operation of the magnetic recording / reproducing apparatus of this embodiment constructed as described above will be described below with reference to FIG.

First, consider the case of reproducing the video information recorded on the magnetic tape 1. The video information recorded on the magnetic tape 1 is detected by the magnetic head 2 and then the video signal processing circuit 4
The well-known reproduction processing (FM demodulation, etc.) is performed in. The video signal subjected to the reproduction processing (hereinafter referred to as the reproduction video signal) is supplied to the digital processing unit 51, subjected to various digital processings, and then output from the output terminal 8. In the digital signal processing unit 51, the reproduced video signal is converted into a digital signal by the A / D converter 12 and then written in the image memory 13. The image memory 13 is controlled by the memory control circuit 15, and the write address, read address, and write / read timing are controlled. The switching circuit 33 is located at the upper side in FIG. 1 (synchronization separation circuit 17) so that the writing to the image memory 13 is performed in synchronization with the horizontal synchronizing signal of the input video signal.
Output side). In addition, A / D converter 12, D / A
The reference clocks of the converter 14 and the memory control circuit 15 are the same as those of the first clock generation circuit 16 as described in the conventional example.
And is configured to be synchronized with the burst phase of the reproduced video signal.

Next, consider a case where the image data written in the image memory 13 by the above-mentioned procedure is recorded at an arbitrary position on the magnetic tape 1. In this case, as described in the conventional example, the switching circuit 6
Is switched to the D / A converter 14 side, and the video signal converted into analog is supplied to the video signal processing circuit 4 and recorded by the magnetic head 2. The switching circuit 34 switches to the second clock generator 31 side and uses a clock that oscillates by self-excitation regardless of the burst phase of the input video signal. As a result, the image memory 13 can be read out stably, and the uneven hue due to the instability of the clock phase as described in the conventional example is prevented. Furthermore, in this embodiment,
The switching circuit 33 switches to the horizontal sync pulse generation circuit 32 side when reading the image memory, generates a stable horizontal sync pulse regardless of the output video signal of the video signal processing circuit 4, and inputs this to the memory control circuit 15. By doing so, the reading operation of the image memory 13 is stabilized. In this embodiment, the horizontal sync pulse generation in the horizontal sync pulse generation circuit 32 is
It is obtained by dividing the output of the second clock generation circuit 31 which oscillates by self-excitation. Further, the switching control of the switching circuits 6, 33 and 34 is performed by the control microcomputer 10, and only when the image data of the image memory 13 is read and recorded on the magnetic tape 1, the above three switching circuits are set to the lower side (first (See the figure).

As described above, according to the present invention, the first clock generating circuit that is phase-synchronized with the burst signal of the video signal, the second clock generating circuit that generates a clock by self-excitation, and the first clock. By providing a switching circuit for switching between the output of the generating circuit and the output of the second clock generating circuit, when writing the image data in the image memory, the output of the first clock generating circuit phase-synchronized with the burst signal is used. When the image data of the image memory is read and recorded on the magnetic tape, the output of the second clock generating circuit that generates the clock by self-excitation is used, so that the image memory can be read with a stable clock. As a result, the excellent effect that the video signal after digital processing can be recorded on the magnetic tape without causing color unevenness is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of essential parts of a magnetic recording / reproducing apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram of essential parts of a conventional magnetic recording / reproducing apparatus. 12 …… A / D converter, 13 …… image memory, 14 …… D / A converter, 15 …… memory control circuit, 16 …… first clock generation circuit, 31 …… clock generation in FIG. Circuit, 34 ... Switching circuit.

Claims (2)

[Claims] 1. An analog / digital converter for converting an input video signal into a digital signal, an image memory for storing a video signal digitized by the analog / digital converter, and a digital read from the image memory. A digital / analog converter for converting a signal into an analog video signal, a first clock generator for generating a clock pulse synchronized with the burst phase of the input video signal, and a free-running separate from the first clock generator Second clock generator for generating the clock pulse of the second clock generator, a first switching circuit for selecting one of the outputs of the first clock generator and the second clock generator, and the first switching circuit. A memory control circuit for controlling the write and read addresses and timing of the image memory based on the output of Video signal recording means for recording the image information written in the memory on a certain section of the magnetic tape, and the first switching circuit on the side of the second clock generator when recording on the magnetic tape. A magnetic recording / reproducing apparatus comprising a control circuit for switching. 2. A horizontal sync separation circuit for separating a horizontal sync signal from an input video signal, and a memory control circuit for controlling writing and reading addresses and timing of an image memory in synchronization with the output of the horizontal sync separation circuit. The magnetic recording / reproducing apparatus according to claim 1, further comprising: