JPS6271387A - Automatic gain adjusting circuit for video signal - Google Patents

Abstract

PURPOSE:To apply accurate automatic gain control by inserting an amplitude reference signal in the blanking period at the recording of a video signal, recording the signal by a recording and processing circuit, using the amplitude reference signal at reproduction to adjust a reproducing signal into a prescribed amplitude by an automatic gain control circuit. CONSTITUTION:The amplitude reference signal from an amplitude reference signal generating circuit 3 is inputted to a recording and processing circuit 4 at a prescribed period in the vertical blanking period via a switch 3 and recorded on a magnetic tape 7 by a rotary head 6 via a recording/reproduction switch 5. A composite video signal inputted from an input terminal 1 at a period other than the prescribed period of the vertical blanking period is inputted to the circuit 4 via the switch 2. The signal reproduced from the tape 7 is given to a reproduction processing circuit 8 via a switch 5 and an amplitude reference signal Sp detected by an amplitude reference signal generating circuit 10 is used to measure the amplitude of the reproduction output, the amplitude is corrected to lead the result to the output terminal 11. Thus, the composite video signal is corrected to a prescribed amplitude over the entire section.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an automatic gain adjustment circuit for video signals that corrects amplitude fluctuations that occur when recording and reproducing video signals.

[Technical background of the invention]

In order to transmit video-related information in a narrow band or record it on a small amount of media, various band compressions and information multiplexing are performed. The high-quality telepino signal has a luminance signal band of 20 MHz and two color signal bands of 5.0 MHz.
It is set to 5~fHz, 7\wound 2, and contains 2 channels of high quality audio signals.

Currently, a band compression technique called the MUSE method is being developed to transmit high-definition television signals over a single channel communication path. In this method, as shown in FIG. 6, the two color signals 8c are compressed on the time axis into '4', and are further multiplexed as a line-sequential signal during the horizontal blanking period of the luminance signal SA. Then, the sub-Nyquist frequency (approximately 1.6M) f that circulates this image signal in 4 fields
) and transmit only at that sampling point.

The horizontal synchronization signal HD is a video signal (color signal Sc and luminance signal S
It is expressed as a specific pattern included in the dynamic range DR of the Y composite signal) and is inserted immediately before the multiplexed color signal Sc.

However, as shown in FIG. 7, in order to simplify the processing on the receiving side, the luminance signal SY is delayed by four horizontal scanning periods from the color signal Sc and sent.

Furthermore, digital signals for interpolation or motion compensation, frame-by-frame signals, and frang level for DC reproduction used on the receiving side are sent using the vertical blanking period.

The two-channel audio signal is PCM transmitted using the remaining vertical blanking period. Then, the audio signal i P
A horizontal synchronization signal is not included in the CiM transmission period.

By the way, in a rotary head type VTR, when reproducing a composite video signal (a composite signal such as a color signal Sc, a luminance signal SA, a synchronization signal, a frame identification signal, etc.) recorded on a magnetic tape, time axis correction of the reproduction output is necessary. will be done.

For this time axis correction, it is necessary to detect a horizontal synchronization signal from the reproduced output of the composite video signal, measure the time axis error, and obtain a control signal for the time axis correction circuit in accordance with this measurement result. This time axis correction circuit is composed of a memory that stores all video signals, and while writing video signals from a VTR (video tape recorder) containing time axis errors into the memory, The video signal and sound are read out from the memory by: Normally, the memory requires a capacity of several H to avoid conflict between the writing and reading operations, and a digital memory is generally used. Therefore, an A/D (analog/digital) converter is provided on the input side of this time axis correction circuit to convert the reproduced video signal from the VTR into all digital data.

In order to effectively utilize the limited number of quantization bits of the Φ converter, it is necessary to match the dynamic range of the reproduced video signal input to the Φ converter with the dynamic range of the Φ converter.

However, it is difficult to match the two dynamic ranges without adjustment due to variations and fluctuations in the characteristics of the recording/reproducing circuit.

Normally, an AGO (automatic gain control) circuit is required to match these two dynamic ranges. This AG
In order to detect the full amplitude of the signal, the O circuit detects the vibration@detection signal included in the signal, and uses this detection signal to adjust the full gain of the variable gain circuit to obtain a signal with a constant field of view.

[Problems with background technology]

However, since the MUSg signal is band-compressed,
It is very difficult to insert the AGO amplitude detection signal without redundant parts, and it is necessary to perform complicated processing such as further time-base compression of the band-compressed MUSE signal.

[Purpose of the invention]

The purpose of this invention is to eliminate the above-mentioned conventional drawbacks.

The purpose of this invention is to provide an automatic gain adjustment circuit for video signals that can perform effective AGO on signals without requiring complicated processing such as time axis compression of M08g signals. [Overview] The automatic gain adjustment circuit for video signals of the present invention inserts an amplitude reference signal necessary for automatic gain adjustment during the blanking period preceding the video signal when recording the video signal, and records it on a recording medium by a recording processing circuit. , the amplitude of the reproduced signal is adjusted to a predetermined amplitude by an automatic gain control circuit using an amplitude reference signal during reproduction.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an automatic gain adjustment circuit for video signals according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, a composite video signal to be recorded is led from an input terminal 1 to one fixed terminal 2a of a switch 2. In FIG. The output signal of the amplitude reference generation circuit 3 is led to the other fixed terminal 2b of the switch 2.

By setting its output to a predetermined amplitude, the amplitude reference signal generating circuit 3 outputs a full amplitude reference signal as shown in FIG. 2 so that the subsequent video signal has a predetermined amplitude.

The movable contact piece 2C of the switch 3 is connected to the fixed terminal 2bK during a predetermined period within the vertical blanking period (a period other than the receiver control signal or audio signal period), and is connected to the fixed terminal 2a during other periods. . Therefore, during periods other than the predetermined period of the vertical blanking period, the composite video signal to be recorded is input to the recording processing circuit 4 through the switch 2, and during the predetermined period of the vertical blanking period, the amplitude reference signal is input to the recording processing circuit 4. 4.

The signal input to the recording processing circuit 4 is subjected to the encoder and FM modulation necessary for recording on a magnetic tape, and when recording, a recording/reproduction switch whose movable contact piece 5c is connected to a fixed terminal 5a is applied. 5 to a rotary head 6 and recorded on a magnetic tape 7.

At this time, the rotational phase of the composite video signal is controlled so that recording of the track is started from the vertical blanking period.

During reproduction, the signal reproduced from the magnetic tape 7 is transferred to the movable contact piece 5.
C is applied to the reproduction processing circuit 8 through the entire recording/reproduction switch 5 connected to the fixed terminal 5b. After being subjected to processing such as FM demodulation and de-emphasis in the reproduction processing circuit 81, the signal is provided to the AGO circuit 9 (automatic gain control circuit).

The AGO circuit 9 is also provided with an output from an amplitude reference signal generation circuit 10. The amplitude reference signal generating circuit 10 is designed to accurately identify the insertion period of the pseudo video signal based on the signal S indicating the rotational phase of the rotary head 6.

The AGO circuit 9 measures the error in the amplitude of the reproduced output using the nine-view width reference signal S detected by the amplitude reference signal generating circuit 10, and according to this measurement result, completely corrects the amplitude of the reproduced output and outputs it to the output terminal 11. I'm trying to guide you.

As described in detail above, in this embodiment, the amplitude reference signal S2 is inserted during a predetermined period of the vertical blanking period, and this amplitude reference signal S is inserted during reproduction.

is reproduced prior to actual information such as a video signal, and the amplitude of the subsequent video signal is all set to a predetermined amplitude by the amplitude reference signal SP.

Therefore, even if the amplitude reference signal SP does not exist in the original composite video signal or does not exist in an appropriate position, it is possible to correct the amplitude to a predetermined value over the entire section of the composite video signal.

Further, according to such a configuration, a special time base compression circuit is not required.

FIG. 3 shows an embodiment in which each field is temporally divided into two and the video signal for one field is recorded on two tracks.

In FIG. 3, the same parts as in FIG. 1 are given the same reference numerals and will be explained. The composite video signal to be recorded is input terminal 1.
The signal is input to the fixed terminal 12m of the switch 12 and the delay circuit 13. The output signal of the delay circuit 13 is input to the other fixed terminal 12b of the switch 12.

The delay circuit 13 has a delay 1 that is half the time width of the vertical blanking period. FIG. 4 schematically shows the composite video signal S1 input from the input terminal 1 and the output signals S and fir of the delay circuit 13.

In this FIG. 4, TV indicates a vertical blanking period.

The movable contact piece 12c of the switch 12 is connected to the fixed terminal 12a in the first half F8 of each field F, and is connected to the fixed terminal 12b in the second half F. Therefore, each field F
In the first half F1, the signal Sl is selected by the switch 12,
In the second half F, the signal S is selected.

As a result, the composite video signal S output from switch 2
, the vertical blanking period TV is reduced by half.

Further, the movable contact piece 12c of the switch 12 is connected to the fixed terminal 12a.
During the period immediately before switching from T1 to the fixed terminal 12b, T1
The content of the video signal during the period T immediately after switching is the same as the content of the video signal during the period T immediately after switching.

Note that the time widths of the periods T1+T2 are equal here, and L7 is half the time width of the vertical blanking period TV, and S is the output of the switch 12.

The period T is the blanking period for the first half F of each field F, and the blanking period for the second half F is shortened to half of the above period T.

It is said that

During a predetermined period T, , T, of the composite video signal output from the switch 2vi switch 12, the output signal of the mold width reference (. All signals are selected and applied to the recording processing circuit 4.

The recording processing circuit 4 is controlled in the same manner as in FIG. 1 above so that the track is updated at the beginning of the insertion period of the imaging reference signal.

However, the operations of the recording processing circuit 4, the recording/playback switch 5, the playback processing circuit 81, the amplitude reference signal detection circuit 10, and the AGO circuit 9 are the same as in the previous embodiment.

The output signal S4 of the AGO circuit 9 is input to the fixed terminal 14m of the switch 14 and the delay circuit 15.

The delay amount of this delay circuit 15 is equal to the delay amount of the previous delay circuit 13, and its output signal S is applied to the fixed terminal 14b of the switch 14.

FIG. 5 shows the output signal S4 of the λGO circuit 9, the output signal S5 of the delay circuit 15, and the output signal S of the switch 14, t?
It is shown schematically. Here, the movable contact piece 14c of the switch 14 is connected to the fixed terminal 1 in the first half F1 of each field F.
4b, and the second half F is connected to the fixed terminal 14a.

Therefore, in the first half F8 of each field F, the signal S is selected, and in the second half F8, the signal S is selected. As a result, the period T1 is removed from the output signal S of the switch 14 as shown in FIG. 5, and a composite video signal having a vertical blanking period called TV is output.

Note that in the above explanation, the case where a composite video signal for one field is recorded on two tracks is explained.
In general, it is possible to record on n (n is an integer of 2 or more) tracks. In this case, the video signal period and vertical pleading/king period TV of each field F are divided into n periods in time and recorded on each track. And amplitude 3
A J ■ Double signal vertical blanking period TV each division period W
j's predetermined period 'iq'i Ic is inserted.

In the above description, this invention has been fully explained using a VTR in which recording and reproduction are performed by one rotary head. VT that performs recording and playback using the head
Of course, it can also be applied to R.

In the case of 7t, 2, it can also be applied to the v1 method of the method of chair 41, which has a method in which all 9 bands are formed between adjacent tracks, and a method in which all guard bands are not formed due to the anomalous recording method. Of course.

In the latter type of VTR, in order to visually minimize crosstalk from adjacent tracks, a method is used in which horizontal periodic signals HD of adjacent tracks are recorded with their positions aligned.

Even when implementing the embodiment shown in FIG. 3 on a VTR of this type, it is possible to align the horizontal synchronizing signal by appropriately setting the delay amount of the delay circuits 13 and 15. .

Furthermore, it goes without saying that the waveforms of the luminance signal and color signal of the amplitude reference signal are not limited to those shown in FIG. According to this method, it is possible to perform accurate AGO without requiring special circuits such as time axis compression, and without being affected by differences in characteristics when a plurality of recording/reproducing circuits are provided.

[Brief explanation of drawings]

FIG. 1 shows the first automatic gain adjustment circuit for video signals of the present invention.
Fig. 2 is a block diagram showing the configuration of an embodiment of the present invention; Fig. 2 is a signal waveform ♂ showing all the amplitude reference signals used in Fig. 1; Fig. 3 is a second embodiment of the automatic gain adjustment circuit for video signals of the present invention; 4 and 5 are signal waveform diagrams for explaining the operation of FIG. 3, and FIGS. 6 and 7 are block diagrams showing the configuration of an example.
The figure is a diagram for explaining a composite video signal of the MTJSE system. 1...Input terminal, 2, 5, 12.14...Switch, 3. 0... Amplitude reference signal generation circuit, 4... Recording processing circuit, 6... Rotating head, 7... Magnetic tape,
8... Reproduction processing circuit, 9... AGC circuit, II...
・Output terminal, 13.15...Delay circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 5

Claims (2)

[Claims] (1) A recording processing circuit that inserts an amplitude reference signal necessary for automatic gain adjustment into a blanking period preceding the video signal and records it on a recording medium when recording the video signal, and An automatic gain adjustment circuit for video signals, comprising an automatic gain control circuit that adjusts the amplitude of a reproduced signal to a predetermined amplitude using an amplitude reference signal inserted in a recording processing circuit during reproduction. (2) The recording processing circuit records the video signal during the blanking period provided in advance of each video signal for each of the video signals divided into multiple parts, and during playback, the automatic gain adjustment circuit records the video signal during the blanking period provided before each video signal. 2. The automatic gain adjustment circuit for video signals according to claim 1, wherein an amplitude reference signal necessary for automatic gain adjustment of the reproduced signal is inserted.