JP2576394B2 - Line sag compensation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line sag compensation system.

[0002]

2. Description of the Related Art When an analog video signal is A / D converted,
DC to replace the DC component of the input video signal
Clamp first. Conventionally, this DC clamp
After the DC component was once removed by a capacitor, the DC component was replaced by a DC clamper. At this time, it is general that an amplification operation is performed by an operational amplifier (op-amp) before and after the processing. FIG. 2 is a block diagram showing an example of a conventional DC clamping method and A / D conversion method.

In FIG. 2, reference numeral 21 denotes an input terminal to which an analog video signal is applied. The input terminal 21 supplies the analog video signal m input from the input terminal 21 to an operational amplifier 22 and a sync separator 29. After the DC component of the video signal n amplified by the operational amplifier 22 is removed by the capacitor 23, the DC clamp is performed by the DC clamp signal t supplied from the DC clamper 28, and the video signal o in which the DC component is reproduced is obtained. The video signal o is supplied to the operational amplifier 24. The operational amplifier 24 supplies the video signal p obtained by performing an amplification operation on the video signal o to the low-pass filter 25. In the low-pass filter 25, the video signal p is band-limited, and the obtained video signal q is converted to an A / D converter 26.
Supply to In the A / D converter 26, the A / D of the video signal q
It performs D conversion and supplies the digital video signal r to the output terminal 27. As a conventional technique related to this kind of line sag compensation method, for example, a technique described in Japanese Patent Application Laid-Open No. 4-298165 is known.

[0004]

In the DC clamping method according to the above-mentioned conventional method, the input bias current of the operational amplifier that performs the amplification operation after the DC clamping is charged in the capacitor, the DC component fluctuates, and the DC clamping is performed. There is a problem that sag occurs in a cycle, that is, a line cycle. The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a line sag compensation method for compensating a line sag generated by charging a capacitor with an input bias current of an operational amplifier that performs an amplification operation after DC clamping. I do.

[0005]

Rainsagu compensation scheme of the present invention, in order to solve the problems], insert the variable current source to cancel the input bias current of the operational amplifier before input terminal of the operational amplifier, A
/ D converted data and vertical blanking period
No signal line part where pedestal level between is maintained
Line sag compensation is performed by feedback-controlling the variable current amount based on the data obtained from the above.
Also, the line sag compensation method according to another invention of the present invention is:
A synchronizing separator for separating a synchronizing signal from an input analog video signal, and a first amplifying and calculating the analog video signal
, A capacitor for removing the DC component of the video signal amplified by the first operational amplifier, a DC clamper for adding a DC component to the video signal from which the DC component has been removed by the capacitor, and a DC clamper A variable current source that adds a set current to a video signal to which a DC component has been added, a second operational amplifier that amplifies and computes a video signal to which the current has been added by the variable current source, and a second operational amplifier. Low-pass filter that limits the band of the amplified video signal, an A / D converter that performs A / D conversion of the video signal that is band-limited by the low-pass filter, and an output of the A / D converter A line sag operation unit for performing a line sag operation in accordance with the timing of the synchronization pulse separated by the synchronization separation unit; Those comprising a current source controller for controlling.

[0006]

According to the present invention, the feedback control of the variable current source is performed using the data after the A / D conversion to cancel the input bias current of the operational amplifier.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a line sag compensation system according to the present invention. In FIG. 1, reference numeral 1 denotes an input terminal to which an analog video signal is applied, 2 denotes an operational amplifier that amplifies and calculates an analog video signal a input from the input terminal 1, and 3 denotes a video signal b amplified by the operational amplifier 1. 4 is a DC clamper for adding a DC component to the video signal from which the DC component has been removed by the capacitor 3, and 5 is a video signal to which a DC component has been added by the DC clamper 4. A variable current source for adding current; 6, an operational amplifier for amplifying and calculating the video signal to which the current is added by the variable current source 5; 7, a low-pass filter for limiting the band of the video signal amplified by the operational amplifier 6 , 8 are A / D converters for performing A / D conversion of the video signal band-limited by the low-pass filter 7, and 9 is an output terminal for sending the digital video signal f to the outside.

Reference numeral 10 denotes a synchronization separation unit for separating a synchronization signal from the input analog video signal a;
Are input terminals and output terminals of the sync separation unit 10. Reference numeral 14 denotes a line sag operation unit for performing a line sag operation in accordance with the timing of the synchronization pulse separated by the synchronization separation unit 9 from the output of the A / D converter 8, and 15, 16, and 17 denote input terminals of the line sag operation unit 14 Output terminal. Reference numeral 18 denotes a current source control unit that controls the current amount of the variable current source 5 based on the calculation result of the line sag calculation unit 14.

Next, the operation of the embodiment shown in FIG. 1 will be described. First, the analog video signal a input from the input terminal 1 is input to the operational amplifier 2 and the input terminal 1 of the synchronization separation unit 10.
Supply to 1. After the DC component of the video signal b amplified by the operational amplifier 2 is removed by the capacitor 3, the DC component is removed by the DC clamp signal i supplied from the DC clamper 4.
Clamping is performed, and a current j supplied from the variable current source 5 is added to obtain a video signal c in which a DC component is reproduced. This video signal c is supplied to the operational amplifier 6. The operational amplifier 6 supplies the low-pass filter 7 with a video signal d obtained by performing an amplification operation on the video signal c. The low-pass filter 7 limits the band of the video signal d, and converts the obtained video signal e to A
/ D converter 8.

Next, in the A / D converter 8, the video signal e
A / D conversion of the digital video signal f
And to the input terminal 15 of the line sag operation unit 14. Then, the synchronization separation unit 10 separates the horizontal synchronization signal and the vertical synchronization signal from the video signal a, and outputs the horizontal synchronization pulse g to the DC clamper 4 via the output terminal 12 and the vertical synchronization pulse h via the output terminal 13. Line sag operation unit 14
Are supplied to the input terminals 16 respectively. The line sag calculation unit 14 calculates a line sag from the no-signal line portion where the pedestal level is maintained during the vertical blanking period, and supplies a signal 1 indicating the calculation result to the current source control unit 18 via the output terminal 17. . This current source control unit 1
At 8, the control signal k is supplied to the variable current source 5 so that the input bias current of the operational amplifier 6 is canceled. The variable current source 5 performs feedback control of the output current j in accordance with the control signal k.

[0011]

As described above, according to the present invention, the feedback control of the variable current source is performed by using the data after the A / D conversion to cancel the input bias of the operational amplifier. This has the effect of compensating for line sag that causes voltage fluctuations due to the charging of the battery.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a line sag compensation system according to the present invention.

FIG. 2 is a block diagram showing an example of a conventional DC clamping method and an A / D conversion method.

[Explanation of symbols]

 2 Operational amplifier (operational amplifier) 3 Capacitor 4 DC clamper 5 Variable current source 6 Operational amplifier (operational amplifier) 7 Low-pass filter 8 A / D converter 10 Synchronous separation unit 14 Line sag operation unit 18 Current source control unit

Claims (2)

(57) [Claims] 1. A variable current source for canceling an input bias current of an operational amplifier is inserted in front of an input terminal of the operational amplifier to obtain data after A / D conversion and a vertical
Signal level that maintains the pedestal level during the
A line sag compensation method wherein a variable current amount is feedback-controlled based on data obtained from an IN portion to perform line sag compensation. 2. A synchronization separation section for separating a synchronization signal from an input analog video signal, a first operational amplifier for amplifying and operating the analog video signal, and a video signal amplified by the first operational amplifier. , A DC clamper for adding a DC component to the video signal from which the DC component has been removed by the capacitor, and a set current added to the video signal to which the DC component has been added by the DC clamper A variable current source, a second operational amplifier for amplifying and operating the video signal to which the current has been added by the variable current source, and a low-pass filter for performing band limitation on the video signal amplified by the second operational amplifier An A / D converter that performs A / D conversion of the video signal band-limited by the low-pass filter; and a timing of a synchronization pulse separated from the output of the A / D converter by the synchronization separation unit. 1. A line sag compensation method comprising: a line sag operation unit that performs a line sag operation in accordance with a signal; and a current source control unit that controls a current amount of the variable current source based on an operation result of the line sag operation unit.