JPS6083472A - Regenerating method of direct current potential of video signal - Google Patents

Abstract

PURPOSE:To regenerate the DC potential of a video signal at a high speed with high precision by detecting a signal potential in a black level period and controlling the potential at the DC operation point of a circuit in front of a detecting circuit for the signal potential. CONSTITUTION:When the DC potential of the black level of a video signal is regenerated, an input signal from an image pickup device is inputted to an amplifier 10 and the potential in the black level period is detected from its output by an OB period potential detecting circuit 11 and compared with a reference potential generated by a reference potential generating circuit 13. A bias voltage generating circuit 14 is controlled according to the potential difference and a bias voltage is generated and fed back to the amplifier 10 so as to reduce the potential difference between the potential in the black level period and the reference voltage. The controlled potential at the DC operation point is held up to the next period.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a DC voltage reproducing method for video signals of TVs, VTRs, etc.

(Structure of the conventional example and its problems) The conventional example will be explained based on FIGS. 1 to 4.

Unlike audio signals, video signals need to be reproduced in a direct current manner from black to white in brightness on a video display device such as a cathode ray tube. For this reason, it is necessary for the camera that images the subject to have frequency characteristics ranging from direct current to a required frequency (generally from direct current to about 5 MHz) on the video display device that reproduces the image. However, it is often technically difficult to create circuits with frequency characteristics derived from direct current. For this reason, a signal that provides an optical black level is included as part of the video signal, and signal processing by an amplifier is normally performed using an electronic circuit using AC coupling. A method is used to reproduce the DC potential based on the optical black level contained in the image.

FIG. 1 shows the signal output of a two-dimensional imaging device such as an image pickup tube or a solid-state imaging device. 1 is one horizontal line of element output (hereinafter abbreviated as IH), 2 is element output IH
In the middle video signal period, 3 is an optical black level (hereinafter abbreviated as OB) period, and 4 is a horizontal retrace period.

To obtain a normal OB, an optical shielding portion is often provided on the imaging device corresponding to the period.

FIG. 2 is an example of a conventional DC potential regeneration circuit. C is a capacitor, D is a diode, and R is a resistor. The circuit shown in FIG. 2 is a circuit called a diode clan, and sets the lowest potential of the input signal to the ground level.

That is, when the signal waveform shown in FIG. 1 is input from the input terminal, the signal potential in the OB period 3 and the horizontal retrace period 4 is fixed to the ground level, and DC potential reproduction is possible. If both the ground-side terminals of the diode crank resistor R are set to the potential level, it is possible to set the signal potential of the input signal during the OB period 3 and the horizontal blanking period 4 to V ie voltage level.

In the example shown in FIG. 2, it is necessary to perform DC potential regeneration including the potential during the horizontal retrace period 4, but if there is large noise in the horizontal retrace period 4, for example, the DC regenerated potential becomes unstable. For this reason, a DC potential regeneration circuit shown in FIG. 3 is currently commonly used. FIG. 3 shows another example of the conventional DC potential regeneration circuit. C is a capacitor, R is a resistor, TR
is L-Lannostar, and B is a DC power supply.

The operation of the circuit shown in FIG. 3 will be explained using FIG. 4.

FIG. 4(a) shows the input signal waveform, and FIG. 4(b) shows the clamp pulse waveform for DC potential regeneration. 3 to 4 are the same as in FIG. 1, and 5 is a clamp period. The input signal shown in FIG. 4(a) is input from the input terminal in FIG. 3, and the clamp pulse shown in FIG. 4(b) is applied to the 77°/'? input from the pulse input terminal.

The clamp period 5 of the clamp pulse is synchronized with the OB period 3 of the input signal. During this Franz 0 period 5, the trannostar TR is turned on and the potential of the DC power supply B is transmitted to the collector side of the transistor TR. As a result, the OB period 3 is fixed to the potential of the DC power supply B as a signal output.

Even after the clamp period 5 ends, the potential of the DC power supply B is stored by the capacitor C and held until the next clamp period. The signal inputted from the input side during periods other than the flange period changes with reference to the potential set during the Franz 0 period 5. That is, the potential during OB period 3 is DC power supply B.
It is fixed at the potential of , and the DC potential is regenerated and output in a dead state.

In the conventional example, the DC reproduction potential is stored in the capacitor C. Therefore, in periods other than clamp period 5,
To prevent the charge of capacitor C from discharging within IH, the time constant, which is the product of capacitor C and the input impedance of the next stage, is set to IH (approximately 64 μsec in the NTSC system).
) or more. Normally, from the viewpoint of circuit stability, etc., the time constant is set to be sufficiently longer than IH. Therefore, when the input signal changes suddenly, due to the above-mentioned time constant,
There was a drawback that DC potential regeneration could not be performed with sufficient response speed.

(Objective of the Invention) An object of the present invention is to provide a method for reproducing a video signal DC potential, which eliminates the drawbacks of the above-mentioned conventional example and can reproduce the DC potential of a video signal at high speed and stably.

(Structure of the Invention) The method for reproducing a video signal DC potential of the present invention is to
In order to detect the signal potential of the B-sentence period black level and set the signal potential to a constant reference potential, the signal potential is fed back to the circuit before the detection circuit, and the potential of the DC operating point of that circuit is controlled. The potential of the controlled DC operating point is the following OB
Retained for a period of time. In this way, by always fixing the potential during the OB period to a constant potential and performing DC regeneration for the next IH period, even if the potential of the input signal fluctuates for each IH, the OB
During the IH period following the punishment period, DC is always regenerated to a constant potential, and I
It is also possible to absorb potential fluctuations in the input signal for each H.

(Description of Embodiment) An embodiment of the present invention will be described based on FIGS. 5 and 6.

FIG. 5 shows a configuration diagram of an embodiment of the present invention.

In the figure, 10 is an amplifier, 11 is an OB period potential detection circuit, 12- is a potential comparison circuit, 13 is a reference potential generation circuit,
14 is a bias voltage generation circuit, and 15 is a bias voltage holding circuit. The input signal is shown in FIG. 4(,), and the clamp signal is shown in FIG. 4(b).

The operation of the video signal black level DC reproduction method configured as described above will be described below.

An input signal from an imaging device is input to a digital amplifier 10 . An OB period potential detection circuit 11 detects an OB period potential from the output, and compares it with a reference potential generated by a reference potential generation circuit 13.

The bias voltage generation circuit 14 is generated based on the difference from the OB prison period reference potential.
A bias voltage is generated and fed back to the amplifier 10 so as to reduce the potential difference between the OB period potential and the reference potential. This OB period potential detection, comparison with the reference potential, generation of bias voltage, and feedback to the amplifier are performed at high speed, and the potential difference between the OB period potential and the reference potential is made zero during the OB period.

Immediately before the end of the OB period, the bias voltage to be fed back to the amplifier is stored in a bias voltage holding circuit, and the feedback roof 0 is cut off outside the OB period. In addition, to recognize the OB sentence period, a Franz 0 pulse synchronized with the OB sentence period is used to recognize the OB sentence period.
During the B period, the potential detection and bias voltage holding circuits are activated.

As described above, according to this embodiment, since the DC potential reproduction of the 1H period of the video signal is performed during the immediately preceding OB period, it is possible to realize high-speed DC potential reproduction. For example, when a video signal in which the black level 21 changes every IH period as shown in FIG. 6(a) is input, a sufficient response cannot be obtained with the conventional DC potential reproduction method, and the output is There is almost no difference from the input signal shown in a). However, when the DC potential regeneration method according to the present invention is used, the output shown in FIG. 6(b) is obtained, and stable DC potential reproduction of the black level 22 can be performed. Note that the transient signal 23 in FIG. 6(b)
can be canceled using the blanking signal, so there is no problem.

Although the output signal of a two-dimensional imaging device is used as the input signal, it is also possible to use the output signal of a one-dimensional imaging device, or the output signal of a video equipment such as a small video tape recorder.

(Effects of the Invention) According to the present invention, when reproducing the black level DC potential of the video signal, the black level signal potential in the video signal is detected and the signal potential is set to a constant reference potential. Furthermore, by controlling the potential at the DC operating point of the circuit before the signal potential detection circuit, it is possible to reproduce the DC potential of the video signal at high speed and with high precision, and its practical effects are outstanding.

[Brief explanation of the drawing]

Fig. 1 is a signal output diagram of an imaging device, Fig. 2 is a circuit diagram showing an example of a conventional DC potential regeneration circuit, Fig. 3 is a circuit diagram showing another example, and Fig. 4 (, ) is a DC potential regeneration circuit. 4(b) is a clamp pulse diagram, FIG. 5 is a block diagram of the DC potential reproducing circuit according to the present invention, and FIG. 6(a) is an input signal diagram of the reproducing circuit. Figure (b) is also an output signal diagram. 1 horizontal period (IH), 2 video signal, 3 optical black level (OB) period, 4 horizontal retrace period, 5 clamp period, io amplifier, 11 OB period Potential detection circuit, 12... Potential comparison circuit, 13. Reference potential generation circuit, 14. Bias voltage generation circuit, 15. Bias voltage holding circuit, 21.. Video signal before DC potential reproduction, 22. DC potential reproduction. Later video signal, C capacitor,
D...Diode, R...Resistor, TR/Transistor. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] A detection circuit detects the black level signal potential in the video signal,
By feeding back the potential difference between the signal potential and the reference potential from the detection circuit to the previous stage, the signal potential is set to the reference potential and the black level DC potential of the video signal is reproduced. Video signal DC potential regeneration method.