JPH04360473A - Correlation duplicate sampling circuit - Google Patents

Abstract

PURPOSE:To eliminate crosstalk noise mixed for an OB period by applying an output signal of a 2-dimension CCD sensor to a differential AGC amplifier during a blanking period including the OB period. CONSTITUTION:A signal outputted from a 2-dimension CCD sensor 1 receiving an optical video signal is subject to correlation duplicate sampling in a clock timing from clock input terminals 10,11 and inputted to one input of a differential AGC amplifier 4. Moreover, a signal resulting from applying correlation duplicate sampling to an output signal of the CCD sensor 1 selected by an analog switch 7 is inputted to the other input of the differential AGC amplifier 4 for a blanking period including an OB period as a reference signal. On the other hand, the switch 7 is thrown to the position of a capacitor connecting to GND for other video signal period than the blanking period.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a correlated double sampling circuit, and more particularly to a correlated double sampling circuit for processing the output of a two-dimensional CCD sensor of a VTR camera.

0002

[Prior art] Conventional VTR cameras are NTSC and PAL.
, SECAM system is adopted, which uses a correlated double sampling circuit to process the two-dimensional CCD sensor output.

FIG. 2 is a diagram of a correlated double sampling circuit showing an example of such a conventional technique. As shown in FIG. 2, the conventional correlated double sampling circuit includes a two-dimensional CCD sensor 1 that inputs and detects optical image information, and a clock input terminal 10 that controls the feed-through period of the output signal output from the two-dimensional CCD sensor 1. It has a first feedthrough clamp circuit 2 that clamps to a specific DC reference level based on clock timing from the clock input terminal 11, and a first sample and hold circuit 3 that samples and holds the video signal based on the clock timing from the clock input terminal 11. The output of this first sample and hold circuit 3 is supplied to one of the differential inputs of a differential AGC amplifier 4. Furthermore, the conventional correlated double sampling circuit has exactly the same configuration as the first feed-through clamp circuit 2 and the first sample-and-hold circuit 3 in order to supply a predetermined potential to the other input of the differential AGC amplifier 4. A second feedthrough clamp circuit 8 and a second sample hold circuit 9 are provided, and the differential AGC amplifier 4 subtracts the signals from the clock input terminals 10 and 11 to remove sampling noise. Video signals are being output.

0004

[Problem to be solved by the invention] The above-mentioned conventional correlation 2
Since the heavy sampling circuit generates the reference signal input to the differential AGC amplifier from a specific DC reference level in the feed-through clamp circuit, it is possible to remove sampling noise caused by internal clocks, etc. The disadvantage is that it is not possible to remove crosstalk noise that occurs during the optical black (OB) period.

[0005] An object of the present invention is to eliminate correlation 2 which can also remove crosstalk noise mixed into the OB period.
The object of the present invention is to provide a heavy sampling circuit.

[0006]

[Means for Solving the Problems] A correlated double sampling circuit of the present invention clamps the feedthrough level of an output signal in a two-dimensional CCD sensor of a VTR camera and samples and holds a video signal. A first feed-through clamp circuit and a first sample-hold circuit for creating a video signal obtained by correlating double sampling of the output of the two-dimensional CCD sensor, and a reference DC for removing sampling noise.
The second step is to create a signal with correlated double sampling of the level.
a differential input AGC amplifier that differentially inputs the outputs of the first and second sample and hold circuits, and an optical black period of the output signal of the two-dimensional CCD sensor. The reference DC during the blanking period including
The level correlated double sampling input is input to the two-dimensional CCD.
The sensor has a switch for switching to the output signal of the sensor, and is configured to remove noise due to crosstalk during the optical black period.

[0007]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a correlated double sampling circuit diagram showing one embodiment of the present invention. As shown in FIG. 1, this embodiment has a configuration in which an analog switch 7 is added as a means for switching the input of the second feed-through clamp circuit 8 in the conventional example shown in FIG. That is, the signal output from the two-dimensional CCD sensor 1 into which the optical video signal is input is subjected to correlated double sampling at the clock timing from the clock input terminals 10 and 11 in the feedthrough clamp circuit 2 and the sample hold circuit 3, and the difference is It is input to one of the differential inputs of the dynamic AGC amplifier 4. Also,
The other differential input of the differential AGC amplifier 4 has . During the blanking period including the OB period, the output signal of the two-dimensional CCD sensor 1 switched by the analog switch 7 is fed through the feed-through clamp circuit 8 and the sample hold circuit 9 by the blanking signal input from the blanking signal input terminal 6. A signal subjected to correlated double sampling is input as a reference signal. On the other hand, during the video signal period other than the blanking period, the analog switch 7 is switched to the capacitor connected between it and GND, and the specific DC reference level in the feed-through clamp circuit 8 is set to the clamp circuit 8 and sample hold circuit 9. The correlated double sampled signal is supplied to the other differential input of the differential AGC amplifier 4 as a reference signal.

[0009]

As explained above, the correlated double sampling circuit of the present invention outputs the output signal of the two-dimensional CCD sensor during the blanking period including the OB period, and outputs the output signal of the two-dimensional CCD sensor during the other video signal periods. A reference signal obtained by correlating double sampling of a specific DC level in the clamp circuit is
By supplying it to the GC amplifier, the crosstalk noise in the two-dimensional CCD sensor during the OB period can be removed by the differential AGC amplifier, and stable OB clamping can be performed even when OB clamping is performed by the subsequent process amplifier, etc. There is an effect that it can be done.

[Brief explanation of drawings]

FIG. 1 is a correlated double sampling circuit diagram showing one embodiment of the present invention.

FIG. 2 is a diagram of a correlated double sampling circuit showing a conventional example.

[Explanation of symbols]

1 Two-dimensional CCD sensor 2, 8 Feed-through clamp circuit 3, 9
Sample hold circuit 4 Differential input AGC amplifier 5 Output terminal 6 Blanking signal input terminal 7 Analog switch 10, 11 Clock input terminal

Claims (2)

[Claims] Claim 1: Clamping the feedthrough level of an output signal in a two-dimensional CCD sensor of a VTR camera,
In a correlation double sampling circuit that samples and holds a video signal, the output of the two-dimensional CCD sensor is
A first feed-through clamp circuit and a first sample-hold circuit for creating a heavily sampled video signal, and a reference D for removing sampling noise.
a second feed-through clamp circuit and a second sample-and-hold circuit that create a signal obtained by correlating double sampling of the C level; and a differential input AGC amplifier that differentially inputs the outputs of the first and second sample-and-hold circuits. and,
The reference D during a blanking period including an optical black period of the output signal of the two-dimensional CCD sensor.
The C-level correlated double sampling input is converted into the two-dimensional CC
A correlated double sampling circuit, comprising a switch for switching to an output signal of a D sensor, and removing noise due to crosstalk during the optical black period. 2. The correlated double sampling circuit according to claim 1, wherein the switch is an analog switch and is controlled by a blanking signal.