JPH1098674A - Agc circuit for video signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AGC circuit for a video signal with well-balanced output amplitude and capable of performing a stable operation of an AGC by optionally setting a function timing of the AGC circuit even when a specific video signal such as macro vision specification is inputted. SOLUTION: This AGC circuit for the video signal is provided with an input 1, an AGC 2, a synchronizing clamp 3, an output 4, an LPF 5, a clamp 6, a Sync.Sep7, an AGC.PG8 and an AGC pulse controller 100 to control the AGC 2 via an AGC controller 10 by turning an AGC pulse generated by the AGC.PG8 on and off. Consequently, the operation of a Sync (synchronizing type) AGC is optionally controlled and the accurate AGC operation is simultaneously obtained even when the specific video signal such as the macro vision specification is inputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an AGC (automatic gain control) circuit for a video signal in, for example, a video tape recorder (VTR), and more particularly, to arbitrarily control AGC operation / non-operation during one field period. Thus, the present invention relates to a video signal AGC circuit for stabilizing the operation of the AGC circuit.

[0002]

2. Description of the Related Art A video recording / reproducing apparatus such as a VTR includes an AGC circuit for automatically controlling the gain of an amplifier circuit so that the level of an input video signal (hereinafter also referred to as "video signal") is kept within an allowable value. Is provided. The AGC circuit is mainly classified into a synchronous (Sync) type and a top value (Peak) type. The Sync AGC circuit performs an operation to keep the Sync level constant in response to the all-horizontal synchronization signal.

FIG. 3 is a block diagram showing an example of a conventional video signal AGC circuit. The conventional video signal AGC circuit shown in FIG. 3 includes an AGC 2 for performing AGC processing on a composite video signal input from an input 1 and a synchronous circuit. In addition to the clamp 3, the output 4, and the low-pass filter (hereinafter simply referred to as "LPF") 5, the clamp 6, the synchronization separation circuit (Syn)
c. Sep) 7, an AGC pulse generator (AGC.
AGC 2 is controlled via an AGC controller 10 by an AGC loop including a PG) 8 and an AGC comparator (AGC.Det) 9.

That is, a low-frequency component is extracted by the LPF 5, and a video signal whose pedestal level is fixed by the clamp 6 is obtained from Sync. Sep. 7, the synchronization signal is separated, and AGC. In PG8, Sync. An AGC pulse is generated at a pedestal timing with respect to the Sync pulse obtained from Sep7. AGC. In Det9, a normal read video signal output from the LPF 5 and the AGC. At the timing of the AGC pulse generated by PG8, the potential of the pedestal (the details will be described later, Sync
, The AGC controller 10 controls the AGC 2 based on the error current obtained by the comparison.

That is, in this type of AGC circuit, in most cases, the AGC circuit uses the sync pulse of the input composite video signal to generate the AG signal.
C. An AGC pulse is generated by PG8,
The control of the AGC is performed by comparing with a pedestal potential which is a specified value at a pulse timing. Therefore, during one vertical period, the value of Syn which is larger or smaller than the specified value
If c levels are mixed and input, large or small Sy
The AGC level was deviated to the side having the higher nc level ratio.

On the other hand, in order to prevent copying of video software in a VTR or the like, pseudo Sy is set within a vertical blanking period of a video signal as shown by a macrovision standard input signal B in FIG.
nc (copy guard signal) is inserted to perform copy guard. The video signal on which the pseudo Sync is superimposed can be monitored by a television receiver, but when applied to a device such as a VTR, the pseudo sync, which is randomly inserted by the AGC circuit, is detected and the image is darkened, thereby increasing the brightness. Was repeated to generate an unbearable signal to prevent copying.

However, the conventional video signal AGC
When the macro vision standard input signal B as shown in FIG. 2 is input to the circuit, there is a problem that the output amplitude of the AGC circuit becomes larger than a specified value. That is, in the macrovision standard input signal B, the vertical blanking period and the vertical synchronizing signal (hereinafter simply referred to as “V
−Sync ”level is 40 IRE, while the horizontal synchronizing signal (hereinafter simply referred to as“ H-
Sync)) level is 30 IRE. The number of Syncs existing in one vertical section is 30IR.
Since there are many ESsyncs, the AGC circuit operates to return from 30 IRE to 40 IRE, and there is a problem that the entire output amplitude becomes larger than a specified value. This means
For example, there is a problem in that even if pseudo Sync is detected, the entire screen becomes bright and it is difficult to express a dark screen.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and the problem is that even when a special video signal such as the macrovision standard is input to the AGC circuit, the output amplitude is reduced. An object of the present invention is to provide an AGC circuit for a video signal which enables stable AGC operation by setting the operation timing of the AGC circuit arbitrarily without deviation.

[0009]

According to the present invention, there is provided a video signal AGC circuit for detecting a level of an input video signal and controlling a gain of an amplifier circuit in accordance with the detected level. The AGC circuit of (1) is provided with AGC control means capable of setting an AGC operation state and an AGC non-operation state during one field (one vertical) section of an input video signal.

As a specific configuration of the AGC circuit for a video signal of the present invention, a synchronization separation means for separating a synchronization signal from an input video signal, and a pulse generation for generating an AGC pulse based on the synchronization signal input from the synchronization separation means Means (AGC pulse generator), comparing means (AGC comparator) for comparing the pedestal level of the input video signal at the timing of the AGC pulse with a predetermined value, and an error current obtained by the comparing means. A video signal AGC circuit including control means (AGC controller or the like) for controlling the AGC by using an AGC pulse based on a control signal separately supplied from a microcomputer or the like while being connected to the pulse generation means. Control of AGC by controlling on / off of AGC Means (AGC pulse controller)
It comprises.

Therefore, in the AGC circuit for video signals of the present invention, an AGC pulse controller for controlling the operation / non-operation of the AGC through the ON / OFF of the AGC pulse based on a control signal separately supplied from a microcomputer or the like. Therefore, the operation of the Sync AGC can be arbitrarily controlled by arbitrarily generating and applying the control signal of the AGC pulse controller. In addition, even when a special video signal such as a video signal of the macrovision standard is input to the video signal AGC circuit of the present invention, the control signal of the AGC pulse controller is arbitrarily generated and applied, so that accurate Sy
The ncAGC operation can be realized.

[0012]

Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

First, the configuration of the video signal AGC circuit of the present invention will be described with reference to FIG. FIG. 1 is a block circuit diagram showing an example of an AGC circuit for a video signal according to the present invention.
Parts common to those described in the related art are denoted by the same reference numerals, and description thereof will be partially omitted.

AGC of the video signal of the present invention in FIG.
The circuit configuration includes an input 1, an AGC 2, a synchronous clamp 3, an output 4, and a low-pass filter (LPF) 5, a clamp 6, a synchronous separating circuit (Sync. Sep) 7, an AGC pulse generator (AGC. PG) 8, and an AGC comparison. AGC loop consisting of AGC.
In addition to the conventional circuit for controlling the AGC 2 via the C controller 10, the AGC. PG8
And an AGC pulse controller 100 as AGC control means for controlling ON / OFF of the AGC pulse of the first embodiment. The control of the AGC pulse controller 100 is performed by a control signal generated from a microcomputer (not shown). The video signal AGC circuit of the present invention is an example of the configuration, and the configuration of the present invention is not limited to the above-described configuration, and it is needless to say that another configuration having the same function may be used. It is.

AGC of the video signal of the present invention having such a configuration
The operation of the circuit will be described with reference to FIGS. FIG. 2 is a timing chart showing the operation of the video signal AGC circuit of the present invention.

From the composite video signal obtained through the LPF 5 and the clamp 6 shown in FIG.
nc. At Step 7, the synchronization signal is separated. AGC. PG
8, Sync. An AGC pulse is generated at a pedestal timing with respect to the Sync pulse obtained from Sep7. At this time, AGC. AGC generated by PG8
Pulse is the newly added AGC pulse controller 1
00, on / off control is performed based on a control signal supplied from a microcomputer (not shown).

With the addition of the AGC pulse controller 100, the conventional AGC2 operates over the entire vertical section corresponding to the input Sync, but the input Sync is controlled by the AGC pulse controller 100. AGC pulse ON / OFF
Can be split off. That is, clamp 6, Sy
nc. Sep 7, AGC. PG8 and AGC. Det
9 can be arbitrarily controlled by an AGC pulse controller 100.

AGC. In Det9, a normal read video signal output from the LPF 5 and the AGC. Only the potential of the pedestal is compared at the timing of the controlled AGC pulse generated by the PG8, and the AGC controller 10 controls the AGC2 based on the error current obtained by the comparison.

The control of the AGC loop by the AGC pulse controller is performed as shown in FIG. That is, for the normal input signal A, the “high level”
Operation (AGC ON), and set the “Low level” section to AGC
By applying the control signal a for inactivating (AGC off), AGC is turned off and V-S
AGC is turned on in the ync and vertical flyback sections. Incidentally, even if the above-mentioned control signal a is applied to the macrovision standard input signal B, the AGC is not performed during the video signal section.
Since it is off, the overall output amplitude does not increase.

In addition, Sync in the normal input signal A
Must be formed by 40 IREs,
Even if the control signal "a" is fixed at "high level", no particular problem arises as long as the operation is the same as that of the conventional video signal AGC circuit. Note that the control signal a in this case may be at any timing for the above reason.

However, in the processing of the macrovision standard input signal B as shown in FIG. 2, if the AGC is turned on during the video signal section, the overall output amplitude may increase as described above. The controller 100 applies another control signal as described below.

The pulse timing of the control signal a is set to AGC ON only in the Sync40IRE section for both the normal input signal A and the macrovision standard input signal B. Signal b is Sync40IRE section to A
If the GC is turned on, it reacts to the pseudo Sync section (it may look like 40 IRE or more), and the AGC is correctly performed.
Is not done. Therefore, the control signal b is changed to the pseudo S
AGC is turned off for the SYNC and the video signal section, and V-Sy
Control signal b that turns AGC ON only in nc section
By controlling by applying (pseudo-Sync non-reaction), the entire output amplitude and Sync AGC can be accurately operated even in the case of the normal input signal A and the Macrovision standard input signal B.

The control signal c in FIG.
(Pseudo-Sync reaction) is used when it is desired to intentionally react to pseudo-Sync to reduce the output amplitude, such as when a copy guard is used.
A sync AGC operation can be enabled. Furthermore, the pseudo-sync is applied to the macro vision standard input signal B.
The output amplitude can be controlled to be small by reacting to all of them (when there is a pseudo Sync), and an accurate Sync AGC operation can be performed.

Usually, the time constant of the AGC is set to be large so that the reaction can be performed over several vertical sections (because the image is distorted if the reaction is performed too fast). For this reason, even if the size of Sync in several horizontal sections is other than 40 IRE, it hardly responds.

In a normal video signal, Syn
Even if the size of c deviates from 40 IRE, only the video signal section is unlikely to be completely deviated as in the Macrovision standard. Therefore, even if there is an AGC-off section in one vertical section, the operation of Sync AGC is performed. Causes almost no problem (for example, the control signal c
And normal input signal A and macrovision standard input signal B
Is operated). However, when setting the time constant, AGC
It is necessary to set a capacity (time constant capacity C) and a current that can sufficiently hold the OFF section.

As described above, the AGC circuit for video signals of the present invention includes the AGC pulse controller 100 for controlling the ON / OFF of the AGC pulse independently of the AGC circuit. c
The operation of SyncAGC can be controlled by arbitrarily generating and applying the three types of control signals.

That is, by applying the control signal a, an AGC operation similar to the conventional one can be performed on the normal input signal A and the macrovision standard input signal B. By applying the control signal b, the AGC is performed only in the 40IRE section excluding the pseudo sync.
Since this is turned on, a copy guard non-compliant mode can be set in which only the normal level is maintained without reacting to the pseudo sync. By applying the control signal c, it is possible to set a copy guard mode in which the video level is reduced in response to the pseudo sync.

As a specific effect of the video signal AGC circuit of the present invention, first, the operation can be controlled without changing the configuration of the conventional video signal AGC circuit. There is no accompanying increase in current consumption. Second, it is possible to construct an AGC circuit that operates accurately even when a special video signal (such as a video signal of the macrovision standard) is input. Third, AG
The operation timing of the C circuit can be arbitrarily set by the control signal, and the control of the AGC circuit is simple. Fourth, AG
The operation timing of the C circuit can be arbitrarily switched by a control signal. Fifth, it is possible to arbitrarily control the support or non-support of the copy guard for the video signal of the macrovision standard by the control signal. And the like.

Although the preferred embodiments of the present invention have been described in detail above, the present invention can be implemented in various embodiments other than these embodiments. For example, in the description of the present embodiment, switching between AGC operation and non-operation has been described.
The same operation can be performed even when the operation is performed with the GC current (that is, when the AGC time constant is switched and controlled).

In this embodiment, the control of the AGC pulse controller is performed by the control signal.
The present invention is not limited to this. For example, it can be controlled as a mode signal. Furthermore, the video signal of the macrovision standard has been exemplified as the special video signal, but the same effect can be obtained by applying a control signal corresponding to any special video signal. Further, the device to which the present invention is applied is not limited to the exemplified VTR, but may be an AG.
The present invention can be applied to a television receiver having a C circuit, a recording / reproducing integrated television receiver, and the like, and it goes without saying that the present invention can be developed into various forms without being limited to the above-described embodiment.

[0031]

As described above, the AG of the video signal of the present invention described above is used.
According to the C circuit, since the AGC circuit includes an AGC pulse controller that controls the on / off of the AGC pulse independently of the AGC circuit, the control signal of the AGC pulse controller is arbitrarily generated and applied, so that the Sync signal is transmitted.
The operation of the AGC can be arbitrarily controlled. Also, A
Even when a special video signal such as a macrovision video signal is input to the GC circuit, it is possible to realize an accurate AGC operation by arbitrarily generating and applying the control signal of the AGC pulse controller. Become.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an example of a video signal AGC circuit according to the present invention.

FIG. 2 is a timing chart showing the operation of the AGC circuit for video signals of the present invention.

FIG. 3 is a block circuit diagram showing an example of a conventional video signal AGC circuit.

[Explanation of symbols]

1 ... input, 2 ... AGC, 3 ... synchronous clamp, 4 ...
… Output, 5… low-pass filter (LPF), 6… clamp, 7… synchronization separation circuit (Sync. Sep), 8
... AGC pulse generator (AGC.PG), 9 ...
... AGC comparator (AGC.Det), 10 ... AGC controller, 100 ... AGC pulse controller, A
... Normal input signal, B ... Macrovision standard input signal, C ... Time constant capacity, a, b, c ... Control signal

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Taketoshi Nishi 5-1 Noguchikita, Kokubu-shi, Kagoshima

Claims (10)

[Claims] 1. An AGC circuit for a video signal, which detects a level of an input video signal and controls a gain of an amplifier circuit according to the detected level, wherein the AGC is performed during one field period of the input video signal.
AG that can set the operation state and non-operation state of the circuit
C of video signal characterized by comprising C control means.
GC circuit. 2. The AGC in said AGC control means.
2. The circuit according to claim 1, wherein the setting of the operation state and the non-operation state of the circuit is arbitrarily controlled by a control signal applied as a control pulse for each of a vertical synchronization section, a vertical retrace section, and a video signal section. A of the video signal of
GC circuit. 3. An AGC circuit according to claim 1, wherein said AGC circuit is operated by said AGC circuit in response to an equivalent pulse including a horizontal synchronizing signal and a pseudo horizontal synchronizing signal included in an operation state section of said AGC circuit. The video signal AGC circuit according to claim 1, wherein the AGC circuit is controlled by a pulse. 4. A synchronizing signal separating means for separating a synchronizing signal from an input video signal, and an AGC based on the synchronizing signal inputted from the synchronizing signal separating means.
Pulse generating means for generating a pulse; comparing means for comparing a pedestal level of the input video signal at the timing of the AGC pulse with a predetermined value; and an error current obtained by the comparing means. A
AGC of video signal having control means for controlling GC
AGC circuit connected to the pulse generating means and controlling the operation / non-operation of the AGC based on a separately supplied control signal. circuit. 5. The method according to claim 4, wherein the control of the operation / non-operation of the AGC by the AGC control means is performed by controlling on / off of an AGC pulse generated by the pulse generation means. AG of the described video signal
C circuit. 6. The control signal according to claim 1, wherein the control signal is a control pulse that activates a vertical synchronization period and a vertical retrace period in one field period of the input video signal and deactivates the video signal period. Item 5. An AGC circuit for a video signal according to item 4. 7. The control signal according to claim 1, wherein the control signal is a control pulse that activates a vertical synchronizing period in one field period of the input video signal and deactivates a vertical blanking period and a video signal period. Item 5. An AGC circuit for a video signal according to item 4. 8. The copy guard non-correspondence mode can be selected by setting the control signal to a non-AGC operation in a vertical blanking interval in which a copy guard signal is inserted. AGC circuit for video signals. 9. The control signal according to claim 1, wherein the control signal is a control pulse that activates a vertical retrace interval in one field interval of the input video signal and deactivates a vertical synchronization interval and a video signal interval. Item 5. An AGC circuit for a video signal according to item 4. 10. The video according to claim 9, wherein a vertical guard interval in which a copy guard signal is inserted is set to an AGC operation by the control signal, so that a copy guard compatible mode can be selected. A of the signal
GC circuit.