JPH0879562A - Video signal clamp circuit for electron endoscope - Google Patents

Abstract

PURPOSE: To reproduce video signals with accurate DC components and less errors by clamping digital video signals in real time. CONSTITUTION: The video signals are passed through an amplifier 21, analog video signal provided with no DC component are outputted from a sample-and- hold circuit 22, digital conversion is performed in an A/D converter 23, the data of a video valid period are tentatively stored in a line memory 24 and output to a poststage is delayed. In the meantime, the output video signals of the converter 23 are inputted to a register 26. Further, pulses from a clamping pulse generation circuit 25 are inputted to the register 26 during the horizontal blanking period of the video signals and pedestal level data are outputted from the register 26. The pedestal level data and the signal data of the video valid period in which the output of the memory 24 is delayed are compared with each other and subtraction is operated between them in a subtraction circuit 27, a pedestal level and video signal DC components are fixed and outputted. In such a manner, signals whose clamping positions are after the video valid period are digitally clamped in real time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reproduces a constant DC component when digitizing an analog video signal having no DC component imaged by a solid-state image sensor provided at the tip of an insertion portion of an endoscope. The present invention relates to a video signal clamp circuit of an electronic endoscope for performing.

[0002]

2. Description of the Related Art FIG. 4 shows a video signal clamp circuit of a conventional electronic endoscope, which is an analog video image having no DC component, which is imaged by a solid-state image sensor provided at the tip of the insertion portion of the endoscope. The signal is first amplified by the first amplifier 71 and input to the sync separation circuit 72 and the capacitor 73 for creating a clamp pulse.

When a clamp pulse is generated from the clamp pulse generating circuit 74, the switch 75 is turned on, and the resistor 7 is turned on by the potential of the reference potential generating circuit 76.
The capacitor 73 is charged via 7.

Then, the point A is fixed to the reference potential and the DC component of the video signal is reproduced. Then, the video signal with the fixed DC component is amplified by the second amplifier 78, and then converted into a digital signal by the AD (analog-digital) converter 79 and output. FIG. 5 shows signal waveforms in the operation.

[0005]

However, in the case of such a circuit configuration, when the switch 75 is closed and the capacitor 73 is charged, the charging current of the capacitor 73 is the resistance 77.
Since the capacitor 73 has a time constant due to the capacitor 73, the capacitor 73 cannot be fully charged during the clamp pulse period.

As a result, since the potential at the point A changes and an error from the reference potential occurs, it is not possible to reproduce the DC component with high precision, and it is possible to obtain the high-quality image required for an endoscopic image. I can't.

Further, for example, as shown in the waveform of the video signal in FIG. 3, when the solid-state image pickup device whose clamp position is behind the video signal is used, the reproduction of the DC component by the clamp circuit as described above is 1 Since an image after the horizontal line is generated, an error further occurs, and a highly accurate DC component cannot be reproduced, so that a high quality image required for an endoscopic observation image cannot be obtained.

Therefore, the present invention provides a video signal clamp circuit for an electronic endoscope capable of reproducing a video signal having an accurate direct current component with a small error by clamping a digital video signal in real time. The purpose is to

[0009]

In order to achieve the above object, a video signal clamp circuit for an electronic endoscope according to the present invention is a DC imaged by a solid-state image pickup device provided at the tip of an insertion portion of the endoscope. An analog-digital converter for converting an analog video signal having no component into a digital signal, and a line memory for temporarily storing the digital video signal of the video valid period output from the analog-digital converter And a pedestal level extraction unit for extracting the pedestal level of the digital video signal output from the analog-digital converter by a crank pulse, the signal data of the video valid period output from the line memory, and the pedestal level extraction And a subtraction circuit for comparing and subtracting the pedestal level signal data output from , Characterized by being adapted to digitally clamped in real time the video signal of the video effective period.

[0010]

Embodiments will be described with reference to the drawings. FIG. 2 shows the overall configuration of the electronic endoscope apparatus according to the embodiment of the present invention. For example, at an image forming position of a subject by an objective optical system 3 provided at the tip of the insertion portion 2 of the endoscope 1, for example, Charge coupled device (C
A solid-state image sensor 4 made of a CD) is arranged. 5
Is a light guide fiber bundle for transmitting illumination light that illuminates the observation range.

The connector section 6 of the endoscope 1 connected to the video processor 10 has a drive circuit 7 for amplifying signals input to and output from the solid-state image pickup device 4, and data unique to the endoscope 1. A rewritable read-only memory (EEPROM) 8 in which the above are stored is arranged.

The video processor 10 also serves as an illumination light source device, and illumination light is incident on the light guide fiber bundle 5 of the endoscope 1 from the light source lamp 11.
In the middle of the incident light path, a three-color rotary filter 12 to which three color filters of red (R), green (G) and blue (B) are attached is arranged so as to rotate at a constant speed.
The illumination light of each color of red, green and blue is sequentially incident on the light guide fiber bundle 5 with a time shift.

The output end of the CCD process unit 14 connected to the drive circuit 7 of the solid-state image pickup device 4 has a timing circuit 15.
Is connected to the input end of the video process unit 16 via an output signal from the video process unit 16.
Sent to

The operations of the CCD process unit 14, the timing circuit 15 and the video process unit 16 are performed by a system control unit 17 having a central processing unit (CPU).
Is controlled in conjunction with. Further, the data on the endoscope side is read from the EEPROM 8 connected to the peripheral driver 19 connected to the system control unit 17.

FIG. 1 specifically shows the configuration of the CCD process unit 14 described above. An image pickup signal picked up by the solid-state image pickup device 4 is amplified by an amplifier 21, and then a video signal is outputted by a sample hold circuit 22. Is extracted. The video signal is an analog signal having no DC component. Then, the analog video signal output from the sample hold circuit 22 is converted into a digital video signal by the analog-digital converter 23.

The digital video signal output from the analog-digital converter 23 is sent to the line memory 24,
The data of the video valid period is temporarily stored in the line memory 24. As a result, the output of the video signal to the subsequent stage in the video valid period before the clamp position is delayed.

A register 26 is connected to the signal line branched from the output terminal of the analog-digital converter 23, and a clamp pulse is generated from the clamp pulse generation circuit 25 during the horizontal blanking period of the video signal. , The pedestal level of the video signal is extracted, and the data of the pedestal level is input to the register 26.

Then, the signal data of the video valid period delayed and output from the line memory 24 and the pedestal level data output from the register 26 are synchronously input to the subtraction circuit 27 where they are compared and subtracted. It

As a result, the signal data output from the subtraction circuit 27 always has a fixed pedestal level, and the DC component of the video signal is fixed. In this way, the video signal whose clamp position is behind the video effective period is digitally clamped in real time to reproduce the DC component with high accuracy.

[0020]

According to the present invention, the signal digitized by the analog-to-digital converter is clamped, so that the problem of waveform distortion due to temperature change or the like which originally occurs in the case of an analog signal can be solved, and an accurate signal can be obtained. It is possible to reproduce a video signal having a DC component.

Even if the clamp position is a signal after the video effective period, the video effective period is stored by digitizing, whereby real-time clamping becomes possible, and as a result, it is more accurate. It is possible to obtain a high quality endoscopic observation image by reproducing the DC component.

[Brief description of drawings]

FIG. 1 is a block diagram of a clamp circuit according to an embodiment.

FIG. 2 is a block diagram showing an overall configuration of an electronic endoscope apparatus of an embodiment.

FIG. 3 is a diagram illustrating a video signal waveform of a solid-state image sensor whose clamp position is behind a video signal.

FIG. 4 is a block diagram of a conventional clamp circuit.

FIG. 5 is a diagram showing a conventional signal waveform.

[Explanation of symbols]

 23 analog-digital converter 24 line memory 25 clamp pulse generation circuit 26 register 27 subtraction circuit

Claims (1)

[Claims] 1. An analog-digital converter for converting an analog video signal having no DC component, which is imaged by a solid-state imaging device provided at a distal end of an insertion portion of an endoscope, into a digital signal, and the analog-digital converter. Line memory for temporarily storing the digital video signal of the video valid period output from the, and for extracting the pedestal level of the digital video signal output from the analog-digital converter by the crank pulse. A pedestal level extraction unit and a subtraction circuit for comparing and subtracting the signal data of the video valid period output from the line memory with the pedestal level signal data output from the pedestal level extraction unit and outputting the result are provided. , The video signal during the video valid period is digitally clamped in real time. And a video signal clamp circuit for an electronic endoscope.