JPS60235596A - Binary-coded video signal output circuit - Google Patents

Abstract

PURPOSE:To obtain a video image same in shape as of an object by driving a constant current circuit with a peak voltage of a video signal, using a potential difference between the peak voltage and a prescribed voltage generated across a variable resistor inserted in series with the constant current circuit as a threshold voltage so as to move vertically equivalently the threshold voltage against the amplitude fluctuation of the video signal. CONSTITUTION:A peak voltage detecting circuit 13 detects and hold the peak voltage Vp of a video amplified signal being an output of a video amplifier 1. The video signal 2 is amplified into a desired amplitude by the video amplifier 1, a video amplified signal 3 is obtained, which is fed to one input of a video comprator 5. Further, a threshold voltage 14 fed to the other input of the comparator 5 is a potential Ex which is obtained by applying the peak voltage Vp obtained from the detection circuit 13 to a variable threshold value generating circuit 15 and subtracting a voltage Et=RXI formed from a resistance value R of the variable resistor 7 of the circuit 15 and a constant current I of the constant current circuit 12 from the peak voltage Vp. Thus, the threshold voltage 14 is moved vertically equivalently against the amplitude fluction of the video amplified signal 3.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a two-dimensional system that binarizes a video signal at a certain threshold voltage.
The present invention relates to a digitized video signal output circuit.

[Prior art]

FIG. 1 is a block diagram of a conventional binary video signal output circuit. In Fig. 1, 2 is a video signal, l is a video amplifier, 3 is a video amplified signal, 5 is a video comparator, 7 is a variable resistor, 4 is a dark value voltage (Ef), and 5 is a binary video signal output. be.

Next, the operation will be explained.

The video signal input 2 is amplified to a desired voltage by a video amplifier to become a video amplified signal 3, which is applied to one input terminal of a video comparator 5.

A dark value voltage (Ef) 4 obtained by dividing the voltage E by a variable resistor 7 is applied to the other input terminal of the video comparator 5. Output 6 is obtained.

This situation is shown in FIG. This example is an industrial television (
This shows a case where a video signal 2 from a camera (ITV), etc. is input. In FIG. 2, the video amplified signal 3
is compared with the dark value voltage 4 with OV as a reference, and it can be seen that a binarized video signal output 6 is output for the amplified signal 3 exceeding the voltage 4. Note that 16 is a synchronization signal.

In the conventional binary video signal output circuit configured as described above, when the subject 18 is illuminated by a light source whose illuminance varies, such as a halogen lamp 19, as shown in FIG. The amplitude of the video signal 2 of the subject 18 from the camera 17 fluctuates due to changes in the illuminance of the halogen lamp 19, and as a result, as shown in FIG. ) and the weak case (signal 3b). Therefore, the pulse width of the binarized video signal output 6 (the signal output when the illuminance is strong is shown as 6a, and the signal output when it is weak is shown as 6b) is Ya,
For example, the monitor television 20 in FIG.
, the width S of the image 10 of the subject 18 naturally changes as the illuminance of the halogen lamp 19 changes.

If, for example, a D/A converter is used in place of the conventional variable resistor 7, and the dark value voltage 4 is increased or decreased according to changes in illuminance, an image having the same shape as the subject 18 can be obtained, but generally speaking It has the drawbacks of being difficult to control and expensive.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above, and it drives a constant current circuit with the peak voltage of a video signal, and connects a variable resistor inserted in series with the peak voltage to the constant current circuit. By using the dark value voltage as the potential difference between a constant voltage generated in The purpose of the present invention is to provide a digital video signal output circuit.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 7 is a block diagram of a binary video signal output circuit according to an embodiment of the present invention. In FIG. 7, the same reference numerals as in FIG. 1 indicate the same or equivalent parts, 8 is a first buffer circuit, 9 is a clamp diode, and 10 is a holding capacitor. .10
The circuit 13 detects and holds the peak voltage Vp of the video amplified signal 3 which is the output of the video amplifier 1. 11 is a second buffer circuit, 12 is a constant current circuit, and the buffer circuit 11. A constant current circuit 12 and a variable resistor 7 are connected in series between the output of the peak voltage detection circuit 13 and the ground, and a variable dark value generating circuit 15 connects these 7, 1.
1.12, the circuit 15 is driven by the peak voltage Vp held in the detection circuit 13, and from the peak voltage Vp a constant voltage Et generated by the resistance value R of the variable resistor 7 and the constant current I. The voltage decreased by the variable dark value voltage (
Ex) 14 is added to the video comparator 5.

Further, FIG. 3 shows the variable dark value voltage generated by the variable threshold value generating circuit.

In FIG. 3, the same symbols as in FIGS. 2 and 7 indicate the same or equivalent parts, and Wl and W2 are the pulse widths of the binary video signal output 6.

Next, the operation will be explained. Video signal 2 is amplified to a desired amplitude by video amplifier 1 to obtain video amplified signal 3, which is applied to one input of video comparator 5. The dark value voltage 14 applied to the other input of the comparator 5 is obtained by applying the video amplified signal 3 to the peak voltage detection circuit 13 and applying the peak voltage Vp obtained from the detection circuit 13 to the variable dark value generation circuit 15. In addition, the voltage Et=Rxl generated from the peak voltage Vp by the resistance value R of the variable resistor 7 of the circuit 15 and the constant current ■ of the constant current circuit 12
is the potential Ex obtained by subtracting . By doing so, the threshold voltage 14 can be raised or lowered equivalently to fluctuations in the amplitude of the video amplified signal 3.

In FIG. 3, as shown in the figure, the voltage Et is constant with respect to the change in the peak voltage Vp, so the dark value voltage 14
goes up and down, the pulse width Wl of the binarized video signal output 6,
It can be seen that W2 does not change.

In this way, in this embodiment circuit, the constant current circuit 12 is driven by the peak voltage Vp of the video amplified signal 3, and the voltage E is lowered by the constant voltage Et generated in the variable resistor 7 than the voltage Vp.
Since x is the threshold voltage 14, the dark value voltage 14 can be raised or lowered equivalently with respect to the amplitude fluctuation of the video signal 2, and as a result, the 6th
Follow the diagram shown.

〔Effect of the invention〕

As described above, according to the present invention, the peak voltage of a video signal is detected, and the video signal is binarized using a variable threshold voltage that is lower than the peak voltage by a fixed voltage, so that a simple and inexpensive circuit can be used. This configuration has the effect of outputting a binary video signal with no variation in the width of the subject.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional binary video signal output circuit, FIG. 2 is a diagram showing a conventional threshold voltage, FIG. 3 is a diagram showing a threshold voltage according to an embodiment of the present invention, and FIG. FIG. 5 is a diagram showing an ITV camera, FIG. 5 is a diagram showing a monitor TV image, FIG. 6 is a fluctuation waveform diagram of a binary video signal, and FIG. 7 is a diagram of a binary video signal output circuit according to an embodiment of the present invention. It is a block diagram. ■...Video amplifier, 2...Video signal input (video signal), 3...Video amplification signal (video amplifier output), 5...Video comparator, 6...Binarized video signal Output, 7... Variable resistance, 12... Constant current circuit, 1
3...Peak voltage detection circuit, 14...Dark value voltage (variable dark value voltage), 15...Variable threshold generation circuit. In the drawings, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa Figure 1 Figure 2 Time - Figure 3 Time - Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) A video amplifier that amplifies the video signal, a peak voltage detection circuit that detects and holds the peak voltage of the output of the video amplifier, and a variable resistor and constant current circuit that are connected in series between the output of the circuit and ground. a variable threshold generation circuit that generates a variable threshold that is a constant voltage drop from the peak voltage; and a video comparator that compares the output of the video amplifier with the variable threshold and outputs a binary video signal. A binary video signal output circuit characterized by: