JPH0522735A - Burst separating circuit - Google Patents

Abstract

PURPOSE:To provide a burst separating circuit with a small circuit scale where the phase of a burst signal is not distorted at the time of separating the burst signal satisfactory in S/N through a band-pass filter. CONSTITUTION:A synchronization separating circuit 3 separating a horizontal synchronizing signal from the output video signal of a clamping circuit 2, a transistor 8 blanking a video signal from the clamping circuit 2 in grand potential in such a way that the separated horizontal synchronizing signal executes tuning on/off and the band-pass filter 11 with the signal executed blanking by the transistor 8 as an input are provided. The burst signal is obtained from the output of the band-pass filter 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burst added to a video signal for producing a control signal necessary for a time axis corrector for correcting a time axis error included in a reproduced video signal of a magnetic recording / reproducing apparatus. The present invention relates to a burst separation circuit that separates a signal and a burst signal that is a color subcarrier of a composite video signal.

[0002]

2. Description of the Related Art In recent years, there are many magnetic recording / reproducing devices for recording / reproducing a component video signal composed of a luminance signal (Y signal) and two color difference signals (RY signal and BY signal). In these devices, a negative horizontal synchronizing signal and a burst signal are added in a horizontal blanking period of a video signal in a recording system, and frequency-modulated and recorded on a magnetic tape or the like. The horizontal synchronizing signal and the burst signal are for creating a write start signal and a write clock for writing the reproduced video signal in the memory in the time axis corrector provided in the reproducing system.

In a magnetic recording / reproducing apparatus for recording / reproducing a component video signal, a horizontal synchronizing signal and a burst signal are added to the RY signal, and a burst signal is added to the BY signal.
In addition, it is known to perform time-axis compression multiplexing, add a burst signal to the Y signal, and record it on a separate track on a magnetic tape.

FIG. 3 is a waveform diagram of a Y signal to which a burst signal is added and a time axis compression multiplexed signal (referred to as CTCM signal). FIG. 3A shows a Y signal to which a burst signal is added,
(B) is a CTC to which a horizontal synchronizing signal and a burst signal are added
It is a waveform diagram of an M signal. The frequency of the burst signal is set to an integral multiple of one horizontal scanning frequency. The cross point between the rising slope and blanking level of the fourth wave in the Y signal burst signal and the third wave in the CTCM signal burst signal indicates the timing reference point of the Y signal, RY signal, and BY signal. .. In Figure 3, point A is the Y signal and point B is the R signal.
The −Y signal and point C indicate the timing reference point of the BY signal. In the recording system, burst signals are added to the input Y signal, RY signal, and BY signal so that the timing reference points have the same phase. In the reproducing system, a timing reference point is detected, a write start signal for writing the reproduced video signal in the memory in the time axis corrector is formed, and reproduced in the memory.
The signal and the reproduced CTCM signal are written to remove the time axis error, and the CTCM signal is separated into the original RY and BY signals and expanded in the time axis. And from memory, Y, R
By reading the -Y and BY signals at the same timing, the phases of the Y, RY, and BY signals are matched.

FIG. 4 is a block diagram of a conventional burst separation circuit in the above magnetic recording / reproducing apparatus. A reproduction video signal input terminal 1 receives a video signal obtained by frequency demodulating a signal from a magnetic tape, and a clamp circuit 2 for clamping the burst signal portion of the reproduction video signal to a specific potential (eg, ground potential), and a recording circuit. The signals other than the burst signal added by the system are supplied to the blanking circuit 15 for blanking. The video signal whose burst signal portion is clamped to the ground potential is supplied to the sync separation circuit 3, and a horizontal sync signal is separated by a comparator or the like. The separated horizontal synchronizing signal is supplied to the blanking signal generator 16 to generate a blanking signal for blanking other than the burst signal in the video signal. In accordance with this blanking signal, the blanking circuit 15 blanks the signals other than the burst signal. The output signal of the blanking circuit 15 is a bandpass filter 1 whose pass band is the frequency of the burst signal.
1 to obtain a burst signal and output it to the output terminal 17.

Since the horizontal synchronizing signal and the burst signal are added to the horizontal blanking period of the video signal, the section between the rising edge of the horizontal synchronizing signal and the timing reference point of the burst signal is as short as several μs. In particular, in the case of CTCM signals, since they are time-axis compression multiplexed, they are very short, about 1 μs. For this reason, when the video signal is directly passed through the bandpass filter, the rising edge of the horizontal synchronizing signal affects the timing reference point, and the phase added by the recording system is deviated. If the phase of the reference point shifts, the phase of the write start signal generated from this reference point shifts, and the timings of the Y, RY, and BY signals output from the time axis corrector do not match. For this reason, a blanking circuit 15 is provided before passing through the bandpass filter 11.

The bandpass filter 11 is provided to improve the S / N of the burst signal section. If the S / N ratio of the burst signal portion is improved, the accuracy of detecting the timing reference point is improved.

A gate pulse for detecting a timing reference point is formed from the horizontal sync signal separated by the sync separation circuit 3, and a timing reference point is detected from the burst signal output from the band pass filter 11 to reproduce a video signal. Form a write start signal for writing into the memory in the time base corrector. When the reproduced video signal is the CTCM signal, two gate pulses are formed to detect the timing reference points of the RY signal and the BY signal.

FIG. 5 shows the relationship between the output signal of the bandpass filter 11 and the gate pulse and the signal indicating the detected timing reference point. 5 (c) and 5 (d) are output signals of the bandpass filter, where (c) is a Y signal and (d) is a C signal.
This is the case of a TCM signal. (E) and (f) are gate pulses for detecting the timing reference point, (e) is the timing reference point A of the Y signal, and (f) is the timing reference point B of the RY and BY signals. , C for gate. (G) and (h) are signals indicating the detected timing reference points.

[0010]

However, in the above-mentioned conventional configuration, in order to obtain a burst signal having a good S / N through the bandpass filter, a blanking signal for blanking a signal portion other than the burst signal is used. It needs a circuit to generate it. In special reproduction (for example, -1 to +2 times speed reproduction) in the magnetic recording / reproducing apparatus, since the length of one horizontal scanning period changes, counting is performed by a counting circuit using a clock phase-synchronized with the reproduced video signal. Creating a blanking signal. Therefore, there is a problem that the conventional burst separation circuit is large in scale and the number of parts is large.

The present invention solves the above-mentioned problems of the prior art. When a burst signal with a small circuit scale, a reduced number of parts, and a good S / N is obtained through a bandpass filter, the burst is generated by the rising edge of the horizontal synchronizing signal. An object of the present invention is to provide a burst separation circuit in which the signal phase is not disturbed.

[0012]

In order to achieve this object, a burst separation circuit of the present invention is a clamp circuit for clamping a burst signal portion added immediately after a horizontal synchronizing signal of a video signal to a specific potential. A sync separation circuit for separating a horizontal sync signal from the output signal of the clamp circuit; a blanking circuit for blanking the output signal of the clamp circuit with a horizontal sync signal output from the sync separation circuit; And a bandpass filter for passing a predetermined frequency band of an output signal of the circuit.

[0013]

According to the present invention, the horizontal sync signal separated from the sync separation circuit is delayed from the horizontal sync signal of the clamped video signal by the delay time in the sync separation circuit. If the video signal is blanked directly by the horizontal sync signal of, the rising edge of the horizontal sync signal of the video signal is blanked, and the period between the burst signal and the sync signal part of the video signal is widened. The phase of the signal is not disturbed. Further, since the horizontal synchronizing signal from the sync separation circuit is used for blanking directly, it is not necessary to separately provide a blanking signal generating circuit.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a burst separation circuit of the present invention. In FIG. 1, the same operation as that of the conventional example is designated by the same reference numeral. 4, 5, 6, 7, and 10 are resistors, 8 is a PNP transistor whose emitter is grounded to a ground potential, 9 is an NPN transistor, 12 is a positive power source (+5 V in this embodiment) supply terminal, and 13 is a negative power source. (−5V in this embodiment).

The video signal input from the input terminal 1 has its burst signal portion clamped to the ground potential by the clamp circuit 2, and is supplied to the collector of the transistor 8 and the base of the transistor 9 via the sync separation circuit 3 and the resistor 4. It The output stage of the clamp circuit 2 is an emitter follower. The sync separation circuit 3 separates the horizontal sync signal of the video signal and outputs a negative sync signal whose low level is the ground potential and whose high level is + 5V. The horizontal synchronizing signal is supplied to the base of the transistor 8 via the resistor 5.

The resistor 6 is connected between the base of the transistor 8 and the ground, and the resistor 7 is connected between the base of the transistor 8 and -5V. Resistance 5, 6,
The resistance value of 7 is set to such a value that the transistor 8 is turned on when the horizontal synchronizing signal is at a low level and turned off when the horizontal synchronizing signal is at a high level.

When the transistor 8 is off, the video signal from the clamp circuit 2 is directly transmitted to the base of the transistor 9 via the resistor 4. When the transistor 8 is on, a direct current flows from the emitter of the transistor 8 connected to ground to the collector and the emitter of the output stage of the clamp circuit 2 via the resistor 4. Therefore, the emitter follower at the output stage of the clamp circuit 2 is turned off, and the collector potential of the transistor 8 (base potential of the transistor 9) becomes about 0 V (ground potential). That is, when the transistor 8 is turned on, the video signal from the clamp circuit 2 is blanked to the ground potential. Further, since the burst signal portion is clamped to the ground potential by the clamp circuit 2, the potential of the burst signal portion and the potential of the blanked portion match.

The horizontal sync signal output from the sync separation circuit 3 corresponds to the delay time in the sync separation circuit 3 and the clamp circuit 2.
It is delayed as compared with the horizontal synchronizing signal in the video signal from.
Therefore, by the horizontal sync signal from the sync separation circuit 3,
Blanking is performed from a point slightly behind the falling edge of the horizontal synchronizing signal of the video signal to a point slightly behind the rising edge of the horizontal synchronizing signal.

FIG. 2 shows a waveform diagram of the video signal blanked by the horizontal sync signal from the sync separation circuit 3. 2 (p) is a video signal showing the output of the clamp circuit 2,
(Q) is a horizontal sync signal indicating the output of the sync separation circuit 3,
(R) is a waveform diagram of the signal of the base of the transistor 9, that is, the blanked video signal.

The collector of the transistor 9 is a + 5V power source,
The emitter is connected to the −5V power source through the resistor 10, and the transistor 9 and the resistor 10 form an emitter follower. The transistor 9 receives the blanked video signal at its base and drives the bandpass filter 11. By the above operation, the rising edge of the horizontal synchronizing signal of the video signal is blanked, and the period between the burst signal and the synchronizing signal portion is widened.
Does not disturb the phase of the burst signal. Figure 2
2 (s) is a waveform diagram of the blanked video signal (FIG. 2 (r)) output through the bandpass filter 11. FIG. Although the pass band component of the band pass filter remains at the falling edge of the sync signal of the video signal, the phase of the burst signal is not disturbed because the period until the burst signal is widened. S of the burst signal part is generated by the bandpass filter 11.
/ N is improved and the output signal is output to the output terminal 14.

As described above, according to this embodiment, the clamp circuit 2 has the emitter through the ground and the collector through the resistor 4.
In order to blank the rising edge of the horizontal sync signal of the video signal from the clamp circuit 2, the PNP transistor 8 connected to the output stage of the sync separation circuit 3 and turned on / off by the horizontal sync signal output from the sync separation circuit 3 is provided. The phase of the burst signal is not disturbed even through the bandpass filter 11. Further, since the horizontal synchronizing signal output from the sync separation circuit 3 directly blanks the video signal, it is not necessary to separately provide the blanking signal generating circuit described in the conventional example. Further, when applied to the magnetic recording / reproducing apparatus described in the conventional example, even if the timing reference point included in the burst signal is detected from the output signal of the bandpass filter 11, it does not deviate from the phase added in the recording system.

In the above embodiment, the clamp circuit 2
The circuit that blanks the video signal from
Although it is composed of 7 and PNP transistor 8, it may be a switch such as a relay which is controlled by the output of the sync separation circuit 3 and switches between the ground potential and the signal from the clamp circuit 2.

[0024]

As described above, the present invention provides a blanking signal generation circuit for blanking signals other than burst signals by providing a blanking circuit for directly blanking the video signal with the output signal of the sync separation circuit. It is not necessary to provide it separately, the circuit scale can be made extremely small, and the number of parts can be reduced. Further, even if the burst signal is passed through the band pass filter, the phase of the burst signal is not disturbed by the rising edge of the horizontal synchronizing signal of the video signal, and a burst signal with good S / N can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a burst separation circuit according to an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the embodiment.

FIG. 3 is a waveform diagram for explaining a conventional component video signal.

FIG. 4 is a block diagram showing a configuration of a conventional burst separation circuit.

FIG. 5 is a waveform diagram for explaining the operation of the conventional example.

[Explanation of symbols]

 2 Clamp circuit 3 Synchronous separation circuit 4 Resistor 8 PNP transistor 11 Bandpass filter

Claims (1)

Claim: What is claimed is: 1. A clamp circuit for clamping a burst signal portion of a video signal, which is added immediately after the horizontal synchronizing signal, to a specific potential, and a horizontal synchronizing signal is output from the output signal of the clamp circuit. A sync separation circuit for separating, a blanking circuit for blanking the output signal of the clamp circuit with a horizontal sync signal output from the sync separation circuit, and a band for passing a predetermined frequency band of the output signal of the blanking circuit A burst separation circuit including a pass filter.