JP2829886B2 - Head-separated video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an XY address type solid-state imaging device, for example, a CMD imaging device arranged in a camera head unit, and an imaging device control circuit and the like to a camera control unit. The present invention relates to a head-separated type video camera provided in the system.

[Conventional technology]

Conventionally, since it is used as a camera for an electronic endoscope, etc.
As shown in the figure, an image sensor 1 is arranged in a camera head unit 2, and a driving circuit 3 and a video signal processing circuit 4 of the image sensor 1 are arranged in a camera control unit 5, so that the camera head unit 2 and the camera control unit are controlled. A head-separated video camera in which units are connected by a cable 6 has been developed. In FIG. 3, reference numeral 7 denotes a preamplifier.

The camera head of such a head-separated video camera is required to be as small as possible.
Therefore, as an image sensor mounted on the camera head,
Since it is composed of one phototransistor per pixel, it is relatively easy to miniaturize the pixel, and the charge modulation device (Charge Modulation Device: CMD) can keep the power consumption within a certain level even at the time of high-speed data reading accompanying the increase in the number of pixels. (Abbreviated as CMD) as a pixel is in the limelight.

Regarding the CMD image sensor, the applicant of the present invention has a national conference of the Institute of Television Engineers of Japan (1986) and Japanese Patent Application Laid-Open No. 60-144072,
FIG. 4 (A) is proposed in Japanese Patent Application Laid-Open No. 60-206063.
FIG. 4B is a cross-sectional view of a unit pixel, FIG.
FIG. 7C shows a timing chart of the gate application selection pulses φ _G1 , φ _G2 , φ _G3 , respectively.

As shown in FIG. 4A, the unit pixel 11 of the CMD image sensor includes an n-type epitaxial layer 13 laminated on a p-type substrate 12.
Above, a donut-shaped gate electrode 14 made of polysilicon,
A source 15 of an n ⁺ type diffusion layer is provided inside and outside the gate electrode 14.
And a drain 16 are formed. The unit pixels having such a configuration are arranged in a matrix in the XY direction, and the gate electrodes 14 of the pixels arranged in the X direction are commonly connected to form a pixel selection line 17, and are arranged in the Y direction. The pixel array 21 shown in FIG. 4B is configured as the vertical signal line 18 by connecting the sources 15 of the respective pixels in common. In this configuration example, a 3 × 3 pixel array is shown.

Gate application selection pulses φ _G1 , φ _G2 , φ _G3 shown in FIG. 4C are output from the level mix circuit 23 to the pixel array 21. The level mix circuit 23 outputs the pulse signal V
_A timing signal is received from the vertical scanning circuit 22 to which _ST , V _CK1 and V _CK2 are input, and three values using externally supplied biases V ₁ , V ₂ and V ₃ (accumulation level, readout and overflow level, reset level) This is a circuit that generates level pulses φ _G1 , φ _G2 , φ _G3 .

The output signal current of the pixel connected to the selected pixel selection line 17 is controlled by output pulses φ _S1 , φ _S2 , φ _S3 from the horizontal scanning circuit 24 to which the pulse signals H _ST , H _CK1 , H _CK2 are input. The video signal is read out to the video line 26 via the selected horizontal selection switch 25, converted into a voltage by the load resistance _RL, and detected. 27 is each vertical signal line when not selected
This is a horizontal switch for fixing 18 to a constant potential, and 28
It is adapted to bias V _D is applied in common to all the pixels of the drain terminal.

[Problems to be solved by the invention]

By the way, as shown in FIG. 5, the output signal of 1H (horizontal scanning period) from the CMD image pickup device having the above-described configuration includes a no-signal level V _O and an output level of a pixel of the CMD image pickup device which is shielded in advance. Optical Black Le
vel) and V _OB, it is composed of the optical signal level V _SIG.

In a head-separated video camera, a CMD image pickup device mounted on a camera head unit may be replaced, or various camera head units may be used in combination with a camera control unit at random. When the CMD image sensor is replaced, the signal level fluctuates due to non-uniformity of characteristics between the element manufacturing lots, and even when the camera head unit is replaced, the characteristics of the CMD image sensor mounted on the camera head unit are not changed. The characteristics of the camera control unit do not match.

If the CMD image pickup device in the camera head unit and the camera control unit in the main unit are not used in combination in which the characteristics are adjusted to an optimal state, the following problems occur.
That is, as shown in the equivalent circuit of the CMD pixel in FIG.
When the optimal drain voltage V _D to the MD pixel varies, with the difference level V _A of the optical signal level V _SIG and the no-signal level V _O and the optical black level V _OB for the no-signal level V _O varies,
When the drain voltage V _D becomes larger, the increased drain-source current V _DS is, pairs blooming property is deteriorated.
On the other hand, when the drain voltage becomes small, the drain-source current _DDS decreases and the signal becomes small, so that the S / N against noise of the preamplifier deteriorates. In FIG. 6, _Vsub indicates a voltage applied to the substrate of the CMD image sensor.

Therefore, every time the CMD image sensor of the camera head is replaced or the camera head combined with the camera control unit is replaced, the signal level is checked on a monitor or the like, and the camera control unit is manually replaced. There was a problem that the bias circuit had to be adjusted.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems in a head-separated video camera using a conventional XY address type solid-state imaging device. When replacing the head,
An object of the present invention is to provide a head-separated video camera in which an optimum bias for an XY address type solid-state imaging device is automatically supplied, and manual bias setting is not required.

[Means and actions for solving the problem]

In order to solve the above-mentioned problems, the present invention, as shown in the conceptual diagram of FIG. 1, arranges an XY address type solid-state imaging device 1 in a camera head unit 2 and drives a fixed imaging device 1 In a head-separated video camera provided with a camera control unit 5 and a video signal processing circuit 4 and the like, the camera control unit 5 provides the optical black level V _OB and the no-signal level V _O of the output signal of the solid-state imaging device 1 to the camera control unit 5. Means 8 for detecting a difference level _VA between the detection means 8 and means 9 for generating a control signal for correcting the bias voltage of the solid-state imaging device in accordance with the amount of change in the detection level of the detection means 8; And a bias correction circuit 10 for correcting the bias voltage. Note that the drive circuit is not shown in this conceptual diagram.

In the head-separated video camera thus configured, when the XY address type solid-state imaging device 1 or the camera head unit 2 is replaced, the level detection means 8 uses a new XY address type solid-state imaging device. _A difference level _VA between the optical black level V _OB and the no-signal level V _O is detected, and the control signal generating means 9 is operated in accordance with the change in the detected level.
A bias correction control signal is transmitted. The bias correction circuit 10 automatically corrects the bias voltage based on this control signal, so that the difference level _VA between the optical black level V _OB and the no-signal level V _O is automatically set to a predetermined value. .

〔Example〕

Next, examples will be described. FIG. 2 is a schematic block diagram showing a configuration of a main part of an embodiment of a head-separated video camera according to the present invention. In the figure, 31, 32
Denotes a sample-and-hold circuit provided in the camera control unit 5, and a video signal processing circuit 4 via a cable 6 and a preamplifier 7 for amplifying an image signal from the CMD image sensor 1.
, And samples and holds the optical black level V _OB and the no-signal level V _O of the output signal of the CMD image sensor 1. The sampling and holding of the optical black level V _OB and the no-signal level V _O are easily performed by adjusting the timing and sampling the output signal.

Reference numeral 33 denotes a subtractor for inputting the optical black level V _OB and the no-signal level V _O to obtain a difference level _VA therebetween. _A comparator 34 compares the difference level _VA obtained by the subtracter 33 with a certain reference voltage _Vref and outputs a bias correction control signal. The drain bias correction circuit 35 includes a comparator 34.
Output a correction drain bias in response to a control signal from
It is configured to supply to the CMD image sensor 1.

In the head-separated video camera configured as described above, the output signal from the CMD
When amplified by the above and transmitted to the camera control unit 5 via the cable 6, the optical black level V _OB and the no-signal level V _O are detected and held by the sample and hold circuits 31, 32, respectively. The optical black level V _OB and the no-signal level V _O detected and held by the sample and hold circuits 31 and 32
Is subtracted by the subtractor 33 to obtain the difference level _VA .
The difference level _VA is input to the comparator 34 and compared with the reference value _Vref, and a drain bias correction control signal corresponding to the difference level _VA is transmitted. In the drain bias correction circuit 35,
An appropriate correction address bias is automatically set based on this correction control signal, and is supplied to the CMD image sensor 1.
Thus, the difference level _VA of the output signal of the CMD image sensor 1 is maintained at a predetermined value.

In the above embodiment, as the correction of the bias voltage of the CMD image sensor, although the one that corrects the drain voltage V _D, in the present invention, by correcting the other bias voltage in the same manner, the difference level V _A It is also possible to configure so as to keep the predetermined value.

In the above embodiment, the drain voltage automatically adjusted when the CMD image sensor of the camera head was replaced.
V _D is, by regarding those out of the standard range of CMD image sensor driving defective element, the camera system according to the invention,
It can be used as a means for inspecting a CMD image sensor.

〔The invention's effect〕

As described above based on the embodiments, according to the present invention, even when replacing the XY address type solid-state imaging device or replacing the camera head, the optical signal of the XY address type solid-state imaging device Since the bias voltage is automatically controlled so that the difference level between the target black level and the no-signal level becomes a predetermined value, an effect that complicated manual bias setting is not required is obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a head-separated video camera according to the present invention, FIG. 2 is a schematic block diagram showing a main part of an embodiment of the present invention, and FIG. 4A is a cross-sectional view of a unit pixel of the CMD image sensor, FIG. 4B is a circuit configuration diagram thereof, and FIG. 4C is an operation thereof. FIG. 5 is a diagram showing a 1H output signal of the CMD image sensor, and FIG. 6 is a diagram showing an equivalent circuit of one pixel of the CMD image sensor. In the figure, 1 is a CMD image sensor, 2 is a camera head,
4 is a video signal processing circuit, 5 is a camera control unit, 6 is a cable, 7 is a preamplifier, 8 is a difference level detecting means, 9
Denotes a bias correction control signal generating means, 10 denotes a bias correction circuit, 31 and 32 denote sample and hold circuits, 33 denotes a subtractor, 34 denotes a comparator, and 35 denotes a drain bias correction circuit.

Claims (1)

(57) [Claims] 1. A head-separated video camera in which an XY address type solid-state imaging device is arranged in a camera head unit, and a drive circuit and a video signal processing circuit for the solid-state imaging device are provided in a camera control unit. A camera control unit configured to detect a difference level between an optical black level and a no-signal level of an output signal of the solid-state imaging device; and a bias voltage of the solid-state imaging device according to a variation in a detection level of the detection unit. And a bias correction circuit for correcting a bias voltage based on the control signal. The correction bias voltage from the bias correction circuit determines the difference between the optical black level and the no-signal level. A head-separated video camera, wherein the difference level is set to a predetermined value.