JPH0865578A - Solid state image pickup device - Google Patents

Abstract

PURPOSE: To obtain a solid state image pickup device capable of reducing the effect of a dark current without increasing heat and noise and further saving power consumption for an image pickup element drive circuit. CONSTITUTION: A CCD 17 is built in an electronic endoscope 2. After transferring a transfer gate pulse from a CCD drive circuit 26 constituting a drive circuit 23 through switches S1, S2, a vertical transfer pulse ϕV and a horizontal transfer pulse ϕH are impressed to the CCD 17 through a vertical transfer pulse driver 27a and a horizontal transfer pulse drivier 27b respectively and a photoelectrically converted signal is outputted from a horizontal shift register in the CCD 17. Since electrostatic charge accumulated in the horizontal shift register is turned to a dark current before the device is driven in a succeeding field, the switch S2 is turned on before impressing the transfer gate pulse and a pulse string more than the number of picture elements in one horizontal line is impressed to discharge the charge accumulated in the horizontal shift register.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device for driving a solid-state image pickup device so as to reduce the influence of dark current.

[0002]

2. Description of the Related Art In recent years, solid-state image pickup devices have come to be widely used in image pickup devices in the medical and industrial fields. For example, in the medical field, it is used for an image pickup device in an endoscope.

The prior art is shown in FIGS. 6 to 9. FIG. 6 shows an interline transfer type charge-coupled device (abbreviated as CCD) 70 which is a general solid-state imaging device. This method C
In the CD 70, a photosensitive portion 71 formed of two-dimensionally arranged light receiving elements and a vertical transfer CCD 72 are alternately arranged in the vertical direction with a transfer gate 73 interposed therebetween, and an end (lower end) of the vertical transfer CCD 72. A horizontal shift register 74, which serves as a horizontal transfer unit, is formed adjacent to the vertical transfer CCD.
The signal charge at the end of 72 is structured to be transferred to the horizontal shift register 74 by a vertical transfer pulse.

FIG. 7 shows drive pulses for the CCD 70. The signal charges photoelectrically converted by a phototransistor as a light receiving element forming the photosensitive portion 71 are vertically transferred by a read pulse (transfer gate pulse or field shift pulse) generated once in one field shown in FIG. 7A. It is transferred to the CCD 72.

The charges transferred to the vertical transfer CCD 72 are
By the vertical transfer pulse (φV) shown in FIG. 7A, it is transferred to the horizontal shift register 74 once in one horizontal period, and from the output end pixel by pixel by the horizontal transfer pulse (φH) shown in FIG. 7B. The signals are sequentially output.

Japanese Patent Publication No. 5-23145 discloses a driving method in the case of a CCD which is displayed in a display range narrower than the display range of a monitor due to the progress of miniaturization of the CCD.

The drive signal in the first conventional example is as follows:
The operation is as shown in FIGS. FIG. 8 shows driving signals in one field period, and FIG. 9 shows driving signals in one horizontal period. The read pulse shown in FIG. 8B is transferred to the transfer unit in synchronization with the image output period (display period on the monitor) shown in FIG. 8A, and the vertical transfer pulse (φV) shown in FIG. ) Is output once, the horizontal transfer pulse (φH) shown in FIG. 8C is output as a pulse train corresponding to the number of pixels in the horizontal direction.

The output signal shown in FIG. 8D is output from the CCD 70 by the pulse train of the horizontal transfer pulse (φH). Although the CCD output is continuously shown in FIG. 8D, it is actually output intermittently in each horizontal period as shown in FIG.

That is, the vertical transfer pulse (φV) is output once at the start time of the horizontal image output period shown in FIG. 9A, and the horizontal transfer pulse (φH) shown in FIG. Pulse trains corresponding to the number of pixels are output. After that, at the start time of the next horizontal image output period, the vertical transfer pulse (φ
V) is output once and the horizontal transfer pulse (φH) shown
Is repeatedly output as many pulse trains as the number of pixels in the horizontal direction.

Therefore, the driving pulses in the vertical and horizontal directions are output to the CCD 70 only during the vertical or horizontal period corresponding to the image display area (captured by the CCD 70), and the driving of the CCD 70 is outside the image display area. Is not performed in the non-video display period corresponding to.

In the second conventional example of Japanese Patent Laid-Open No. 55-163962, in the vertical blanking period, in order to prevent the noise due to the dark current of the CCD from being increased by stopping the driving, the blanking period is increased. It is disclosed that the vertical transfer CCD is idle-transferred without stopping the driving for removing the dark current during the period.

[0012]

However, if the driving of the CCD is stopped outside the image area as in the first conventional example, the dark current of the horizontal shift register of the CCD is accumulated, so that the CCD driving is performed. The above-mentioned dark current is added as an error to the first one line that started.

If the CCD is driven even during the blanking period (retrace period) to remove the dark current as in the second conventional example, the φH pulse for driving the CCD is about 8 MHz or more. High frequency, and further CCD and CCD
In the case of a device in which the drive circuit is connected with a cable separately, when the cable is thin or requires a long cable, the capacitive load of the cable becomes heavy, and the output driver of the CCD drive circuit, especially the output driver, is considerably large. Since electric power is consumed, a large-capacity power source and measures for heat generation are required, resulting in a problem that the size of the device becomes large.

In the second conventional method, in order to prevent a dark current by applying a vertical transfer pulse to the vertical transfer section of the CCD 17 and a horizontal transfer pulse to the horizontal transfer section during the vertical blanking period, one field is used. If the horizontal transfer pulse train corresponding to the number of pixels is not applied, the effect is not effective.
Since the vertical blanking period is shorter than the normal drive period, the required idle transfer cannot be executed unless the signal rate is significantly increased for this idle transfer as compared with the case of the normal drive.

Therefore, with this driving method, the CCD must be driven at a frequency significantly higher than the frequency of the normal horizontal transfer pulse train, and the maximum drive frequency allowed is much higher than that of the normal CCD. Things are needed, and very expensive CCDs are needed. Alternatively, it is necessary to drive at a high frequency such as higher than the maximum drive frequency allowed, and the ratio of the power loss in the CCD to the drive frequency is significantly increased compared to the case of normal drive, and the CCD
The heat generated by the CCD does not significantly increase due to the loss in the.

For this reason, the amount of heat generated in the CCD increases and the amount of thermal noise generated also increases. Even if the effect of dark current can be reduced, the S / N is reduced due to thermal noise.

In view of the above problems, it is an object of the present invention to provide a solid-state image pickup device capable of reducing the influence of dark current without increasing thermal noise and enabling power saving of an image pickup element drive circuit. And

[0018]

Means and Actions for Solving the Problems A light receiving element portion comprising a plurality of light receiving elements, and a transfer portion for transferring a photoelectric conversion signal photoelectrically converted by each light receiving element of the light receiving element portion and outputting the signal to the outside. While generating a solid-state imaging device having, a transfer signal for transferring the photoelectric conversion signal of the light receiving element unit to a transfer unit, and a transfer pulse train for applying the photoelectric conversion signal to the transfer unit and outputting the transferred photoelectric conversion signal to the outside. , At a time that precedes the time when the transfer signal is output in a predetermined cycle, has a duration shorter than the predetermined cycle, and has a part of which precedes the transfer signal. By providing a drive circuit that outputs a pulse train, the signal charge that causes dark current accumulated while the transfer unit is not driven is swept from the solid-state image sensor by the pulse train preceding the transfer signal. And, so that not to adversely affect the photoelectric conversion signal after the pulse train.

[0019]

Embodiments of the present invention will be specifically described below with reference to the drawings. 1 to 3 relate to a first embodiment of the present invention, FIG. 1 shows the entire configuration of an endoscope apparatus including the first embodiment, and FIGS. 2 and 3 are for explaining the operation of the first embodiment. The timing chart of is shown.

As shown in FIG. 1, an endoscope apparatus 1 as an image display apparatus having a solid-state image pickup device 6 according to the first embodiment includes an electronic endoscope 2 having an image pickup element built therein, and this electronic endoscope. 2, a light source device 3 for supplying illumination light, and a camera control unit (hereinafter, C) as a signal processing unit that drives an image sensor and performs signal processing on an output signal of the image sensor.
(Abbreviated as CU) 4 and a color monitor 5 for displaying a video signal output from the CCU 4. The solid-state image pickup device 6 according to the first embodiment of the present invention includes an electronic endoscope 2 having an image pickup element built therein and a CCU 4.

The electronic endoscope 2 has a long and flexible insertion portion 7, an operation portion 8 connected to a proximal end portion of the insertion portion 7 and having a bending operation knob (not shown), A universal cable 9 extended from the side of the operation unit 8 to the outside
And a light guide connector 11 is attached to the end of the extended universal cable 9.

The light guide connector 11 can be detachably connected to the light source device 3. By connecting the light guide connector 11 to the light source device 3, the illumination light of the illumination lamp 12 arranged inside the light source device 3 is incident on the end face of the light guide connector 11 via the lens 13. The illumination light is transmitted by the light guide fiber 14 inserted through the universal cable 9 and the insertion portion 7, and the tip portion 1 formed at the front end of the insertion portion 7.
The light is emitted to the front from the emission end face of the light guide fiber 14 attached to the illumination window 5.

An object illuminated by the illumination light emitted from the emission end face is optically imaged on a CCD 17 as a solid-state image pickup element arranged on the focal plane by an objective lens 16 attached to an observation window provided at the tip portion 15. Are tied together.

This CCD 17 is an interline transfer type CC
The CCD 17 has a structure similar to that of FIG.
That is, the photosensitive section (imaging surface) is configured by the light receiving element section in which a large number (a plurality of) light receiving elements having a photoelectric conversion function are two-dimensionally arranged in the horizontal direction (horizontal scanning direction) and the vertical direction (vertical scanning direction). Then, a vertical line-shaped vertical transfer unit (vertical transfer CCD) is provided to each vertical line-shaped photosensitive unit via a transfer gate.
Are formed in an interline shape.

Then, by applying a transfer gate pulse (also referred to as a read pulse) as a transfer signal for transferring to the transfer gate to the vertical transfer portion, the signal charge of the photosensitive portion having a vertical line shape is transferred to the vertical transfer portion. By applying a vertical transfer pulse to the vertical transfer section, the signal charges at the end of the vertical transfer section are transferred to the horizontal shift register as an adjacent horizontal transfer section. Then, a horizontal transfer pulse train is applied to this horizontal shift register in which a plurality of signal storage elements having a function of storing and transferring signals in the horizontal direction are arranged in a horizontal direction (more specifically, horizontal pixels in the photosensitive section). As a result, the signal charges are sequentially output to the outside from the output end at one end of the horizontal shift register.

A color separation filter 18 is attached in front of the image pickup surface of the CCD 17, and for example, each light receiving element is optically color-separated, received by the light receiving element, and photoelectrically converted. The CCD 17 is connected to a signal line 19 inserted through the insertion portion 7 and the universal cable 9, and the signal line 19 is further inserted through a signal cable 21 extended from the light guide connector 11 and connected to the CCU 4. The signal connector 22.

The signal line 19 includes an image pickup element drive circuit (simply referred to as a drive circuit) 23 in the CCU 4 and a signal processing circuit 2.
4 is connected. The drive circuit 23 generates a drive signal for driving the CCD 17 and applies it to the CCD 17 via the signal line 19. The image signal photoelectrically converted by the CCD 17 is transmitted through the signal line 19 and input to the signal processing circuit 24. A standard video signal (video signal) is generated by the signal processing circuit 24, the standard video signal is output to the color monitor 5, and a display area 25 (for an image sensor) on the display surface 10 of the color monitor 5. CCD
The subject image captured in 17 is displayed in color. As shown in FIG. 1, the CCD 17 is constructed separately from the drive circuit 23.

The drive circuit 23 is a CCD drive circuit 26 for generating a vertical transfer pulse φV (and a transfer gate pulse φS synthesized with the first vertical transfer pulse φV) as a drive signal for driving the CCD 17 and a horizontal transfer pulse φH. ,
Φ which outputs these drive signals by pulse current amplification
Switches S1 and S2 provided between the driver 27 having the V driver 27a and the φH driver 27b, the output end of the CCD drive circuit 26 and the input ends of the φV driver 27a and the φH driver 27b, and these switches S1 and S2.
And a drive control circuit 28 for controlling ON / OFF of.

ΦV driver 27a and φH driver 27
b is current-amplified when the level of the input signal inputted exceeds a threshold value set between the “H” level and the “L” level (for example, the median value of the “H” level and the “L” level), and this threshold value is No current amplification is applied to the following input signals,
For example, in the class C amplifier circuit configuration, the power consumption increases only when the vertical transfer pulse φV or the horizontal transfer pulse φH is input (due to the current amplification function), and the power consumption when not input is small. It becomes a value.

On the other hand, the signal processing circuit 24 includes a switch S3 for removing unnecessary components of the signal input from the signal input terminal, and an amplifier 30 for amplifying the signal via the switch S3.
A luminance signal generation circuit 31 that generates a luminance signal from the signal amplified by the amplifier 30, a color signal generation circuit 32 that generates a color signal, and an RGB signal generation circuit 33 that generates an RGB signal from the luminance signal and the color signal. A sync signal generation circuit 34 for generating vertical and horizontal sync signals, and a switch control circuit 35 for controlling the opening and closing of the switch S3 based on the sync signal.

The vertical and horizontal synchronizing signals of the synchronizing signal generating circuit 34 are input to the CCD driving circuit 26, and the CCD driving circuit 26 generates driving signals in synchronization with these synchronizing signals. Further, the vertical and horizontal synchronizing signals of the synchronizing signal generating circuit 34 are also input to the drive control circuit 28, and the drive control circuit 28 generates a control signal for controlling the opening and closing of the switches S1 and S2 in synchronization with these synchronizing signals. To do.

The CCD drive circuit 26 creates drive signals for the vertical transfer pulse φV and the horizontal transfer pulse φH for driving the CCD 17, and outputs them from the output end. Note that the transfer gate pulse φS is internally added to the first vertical transfer pulse φV and the result is output from the output terminal (therefore, FIG. 2C).
Then, φV is represented by (φV + φS)).

The output drive signal, that is, the vertical transfer pulse φV (including the transfer gate pulse φS superimposed on the first vertical transfer pulse φV), the horizontal transfer pulse φH, and the switch S1 controlled by the drive control circuit 28.
After passing through S2, the current is amplified by the driver 27, output, and applied to the CCD 17. And CCD17
The output signal of is processed by the signal processing circuit 24, output to the color monitor 5, and displayed in color in the display area 25.

As shown in FIG. 1, the display area 25 is not the entire area in the vertical direction on the display surface of the color monitor 5,
For example, it is a region near the center excluding both upper and lower ends. Therefore, in the 1-field period, the photoelectric conversion signal imaged by the CCD 17 is output only in the central period excluding both sides thereof, and the display period is displayed.

If the CCD 17 is not driven except during this display period, the photoelectric conversion signal is transferred to the horizontal shift register in the next field period, and the signal by the horizontal transfer pulse train is output, which becomes a dark current accumulated before the transfer. In this embodiment, the transfer gate pulse φ
Prior to the application of S, accumulated in the horizontal shift register,
One of the characteristics is that the drive circuit 23 is provided with a means (more specifically, a horizontal shift register accumulated charge sweeping-out means) for applying a pulse train for sweeping out a charge causing a dark current to the horizontal shift register. In this embodiment, the horizontal transfer pulse φH is used as the pulse train for sweeping out the electric charges that cause the dark current.

Next, the operation of the first embodiment will be described with reference to FIG. FIG. 2 shows a timing chart in one field of the first embodiment. As shown in FIG. 2A, the vertical synchronizing signal is output from the synchronizing signal generation circuit 34 at the start time of one field.

The drive control circuit 28 counts the horizontal synchronizing signal from the vertical synchronizing signal, and turns on the switch S2 at a timing (time) which is, for example, several horizontal periods ahead of the time Tv until the display start timing in the vertical direction. The control signal to turn on is output to switch S2. By this control signal, the switch S2 is turned ON for a short duration T1 as shown in FIG. 2D (“H” level is ON, “L”).
The level indicates OFF).

When the switch S2 is turned on, C
The horizontal transfer pulse φH from the CD drive circuit 26 is applied to the φH driver 27b, and the horizontal transfer pulse φH current-amplified by the φH driver 27b is C as shown in FIG. 2 (e).
It is applied to the CD 17 (Fig. 2 (e) shows the φH driver 27).
b) output).

The CCD 17 is driven by this horizontal transfer pulse φH.
A signal corresponding to the dark current accumulated in the horizontal shift register is output from the output terminal as shown in FIG. In this embodiment, the pulse train (the number of pulses) of the horizontal transfer pulse φH is equal to the number of horizontal signal storage elements of the horizontal shift register of the CCD 17 (the number of horizontal line elements, or the number of horizontal pixels of the photosensitive portion, so one horizontal line). It is about twice the number of pixels (abbreviated as the number of pixels), and most of the dark current components are swept out in the pulse train for the number of pixels in the first horizontal line, and
The signal level of the remaining dark current is generally sufficiently low after the horizontal line pixel. Therefore, it is desirable to apply a pulse train for at least one line element.

After the time T1 for the processing of sweeping out the dark current, the switch S2 is turned off, and at the display start timing in the vertical direction (more specifically, as shown in FIG. At the horizontal display start timing after the lapse of Th), the drive control circuit 28 applies a control signal for turning on the switch S1 to the switch S1.

This control signal is also sent to the CCD driving circuit 26, and the CCD driving circuit 26 superimposes the transfer gate pulse φS on the first vertical transfer pulse φV at the rising edge of this control signal, and the vertical gate shown in FIG. Transfer pulse φV +
Output φS.

When the switch S1 shown in FIG. 2B is turned on, the transfer gate pulse φS and the vertical transfer pulse φV from the CCD drive circuit 26 are applied to the CCD 17 via the φV driver 27a. Then, the transfer gate pulse φS transfers the signal charge of the photosensitive portion of the CCD 17 to the vertical transfer portion, and further the vertical transfer pulse φV transfers the signal for one horizontal line pixel number by one pixel in the vertical direction. Signal charges for one horizontal line pixel number are transferred from the vertical transfer unit to the horizontal shift register.

The switch S2 is turned on in synchronization with the falling of the vertical transfer pulse φV, and the switch S2 is turned on.
In the period T2 after N, the signal charges are sequentially output to the outside as a CCD output signal from the horizontal shift register in the pulse train of the horizontal transfer pulse φH, as shown in FIG.

The period T2 includes a pulse train of horizontal transfer pulses φH for the number of horizontal line pixels. The drive control circuit 28 turns off the switch S2 from the time when the switch S2 is turned on to the time when the horizontal transfer pulse φH is output for one horizontal line pixel number (the switch S2 is turned off).
Drive control circuit 28 for determining the time
May turn on the switch S2 and then count the horizontal transfer pulse φH of the CCD drive circuit 26).

Then, the control operation of turning on the switch S2 in synchronism with the fall of the vertical transfer pulse φV and turning off the switch S2 at the time when the horizontal transfer pulse φH is output for one horizontal line pixel number is repeated. In this way, the signal charges of the last one horizontal line pixel number in the vertical direction (the number of one horizontal pixel at the position most distant from the horizontal shift register in the vertical transfer portion in the vertical direction) are transferred to the horizontal shift register (one field). (Final) Vertical transfer pulse φV
The drive control circuit 28 turns off the switch S1 at a time after the output of.

When the reading of the last one horizontal line pixel number of the horizontal shift register transferred by the vertical transfer pulse φV is completed by the pulse train of the horizontal transfer pulse φH, the drive control circuit 28 also turns off the switch S2. In this embodiment, the vertical transfer pulse φV is output in the same cycle as the cycle of the horizontal synchronizing signal (not limited to this when a memory is provided as described later).

In this way, CC in one field period
When the driving of D17 is completed and the next vertical synchronizing signal is output, the same operation as described above is performed. That is, the driving of the CCD 17 in one field period is completed, the non-driving period is started after this end time, and the charges causing the dark current are accumulated in the horizontal shift register until the driving in the next field. Therefore, in the next field, the sweep process is performed prior to the application of the transfer gate pulse φS. As shown in FIG. 2, the driving of the CCD 17 in one field period is completed before the output period of the next vertical drive signal or the start of the vertical blanking period.

The CCD output signal shown in FIG. 2 (f) is input to the signal processing circuit 24 shown in FIG. In this case, switch S
As shown in FIG. 2G, 3 is turned on for the entire display period T3 in one field from the time when the switch S1 is turned on to the time when the switch S2 is finally turned off, and the switch S1 is turned on. The signal during the sweep processing period before the time is masked without performing the signal processing for display.

Note that the entire display period T3 intermittently includes a horizontal non-display period in which no horizontal display is performed, which will be described below. The entire display period T3 extends in the vertical direction of the display area 25 in FIG. It corresponds to the display area 25V.

FIG. 2 shows the operation for one field period, and the operation in the horizontal period is as shown in FIG. For example, even in the entire display period T3 in one field of FIG. 2, a horizontal display period in which an image is intermittently displayed in each horizontal period is formed.

As shown in FIG. 3A, at the horizontal display start timing after a lapse of a certain time Th from each horizontal synchronizing signal (included in the horizontal period when the display is performed in the vertical direction), the horizontal display start timing shown in FIG. Turn on switch S1 as shown in (b).
The drive control circuit 28 outputs a control signal for controlling.

The switch S1 is turned on at the falling edge of the vertical transfer pulse φV shown in FIG. 3C, and during the period T2 in which the switch S1 is turned on, one horizontal line pixel is displayed as shown in FIG. 3D. A pulse train of several horizontal transfer pulses φH is applied to the CCD 17 via the φH driver 27b.

Then, as shown in FIG. 3 (e), during the period in which the pulse train of the horizontal transfer pulse φH is applied from the CCD 17, light is received by the photosensitive portion of the CCD 17 and photoelectrically converted.
The signals for the number of horizontal line pixels are output from the CCD 17. Therefore, as shown in FIG. 3E, the horizontal transfer pulse φ
The period T2 in which the H pulse train is output is the horizontal image display period or the image output period, and this period T2 corresponds to the horizontal display region 25H in the display region 25 of FIG.

Since the stop period during which the driving is stopped within one horizontal period is extremely shorter than the stop period within the one field period, the accumulation of dark current is small and it is not necessary to perform idle transfer.

As described above, the CCD 17 transfers the photoelectric conversion signal from the photosensitive section to the vertical transfer section once in one field period, but the display period of the image picked up by the CCD 17 is shorter than the one field period.

Therefore, the driving of the horizontal transfer pulse φH is started, for example, several lines before (at least one line pixel number before) from the timing of transfer from the photosensitive part of the CCD 17 to the vertical transfer part, and the charges accumulated in the horizontal shift register are discharged. I try to sweep it out. Therefore, the signal of the photosensitive portion of the CCD 17 is transferred to the horizontal shift register, and the influence of adding the dark current to the photoelectric conversion signal read from the CCD 17 through the horizontal shift register can be reduced, and a video signal with good image quality can be generated. .

The pulse train to be supplied to the φH driver 27b is stored in the horizontal shift register in order to sweep out electric charges which cause dark current, in addition to the horizontal transfer pulse train for outputting the photoelectric conversion signal of the photosensitive portion of the CCD 17 to the outside. By providing a stop period in which the pulse train of is applied for a short duration and not applied in other periods, the φH driver 27b holds the input terminal at the GND level during the stop period.
It is possible to suppress the power consumption of the φH driver 27b during this suspension period to be low.

Furthermore, in order to prevent the dark current, it is not necessary to perform the idle transfer for the pixels displayed in one field in the short vertical blanking period as in the second conventional example, and the horizontal transfer is performed. Pulse train equivalent to pixels for several lines (substantially equivalent to pixels for one line)
Is not necessary to generate a high-rate pulse train, and only a few more horizontal transfer pulses need to be applied than usual.

Therefore, the effect of the dark current can be reduced only by additionally providing a simple circuit, and the amount of extra heat generated by the CCD 17 due to the pulse train for reducing the effect of the dark current is extremely small. However, there is almost no decrease in S / N due to increase in heat generation and thermal noise.

Further, compared with the case where the stop period is not provided as in the second conventional example, the power consumption particularly in the φH driver 27b can be suppressed low. Therefore, φH driver 27b
Power consumption can be reduced, and as a result, the device can be downsized.

In addition, the present invention can be applied to the case where the CCD driving is intermittently output as in the modification shown in FIG. 4 so that the exposure time of the CCD is lengthened and the sensitivity of the CCD is increased.

As shown in FIG. 4 (a), exposure is performed for a plurality of field periods (two field periods in FIG. 4), and one of them is exposed.
By applying the drive signal only during the field period and reading it, the CCD signal level due to the double exposure time is set to 2
Can be doubled.

In this case, since the period during which the CCD is not driven becomes long, the accumulation of dark current also increases. However, as in the first embodiment, the driving is started from the time preceding the output time of the transfer gate pulse φS. By doing so, dark current can be removed.

4 (b), (c), (d) and (e) correspond to (c), (d), (e) and (f) of FIG. In addition, in FIG. 2E, the pulse train for sweeping is almost 2
FIG. 4 shows the case where the number of horizontal line pixels is output.
(D) shows a case where almost one horizontal line pixel is output. This modification also has substantially the same effect as that of the first embodiment.

FIG. 5 shows an endoscope apparatus 41 having the second embodiment.
Indicates. This endoscopic device 41 is the endoscopic device 1 shown in FIG.
The CCU 4 in FIG. 1 is further configured by using a CCU 44 provided with a front panel 43 having several types of switches 42 and the like.

The front panel 43 is connected to the signal processing circuit 45 and turns on several kinds of switches 42 which are variable input sections.
As an input variable (parameter) by the ON / OFF operation, an instruction signal for controlling the change or setting of the AGC level of the AGC circuit 47 is input via the encoder 46.
The freeze ON / OFF can be controlled by outputting to the 5 side or outputting a freeze or freeze release instruction signal to the freeze memory provided in the RGB signal generation circuit 33. The solid-state imaging device 40 of the second embodiment is composed of the electronic endoscope 2 and the CCU 44.

The front panel 43 is electrically connected to an external control circuit 48 which is separate from the CCU 44. The external control circuit 47 can be operated to substitute variables by operating several kinds of switches 42 provided on the front panel 43.

That is, in the CCU 44 shown in FIG. 5, the functions of the CCU 44 (for example, AGC level,
Freeze etc.) can be controlled.

On the other hand, a signal sent from the external control circuit 48 functioning as an external variable input section can act as the switch 42 to control functions such as AGC level. The other structure is similar to that of FIG.
It has substantially the same operation and effect as the embodiment.

In the above embodiment, the CCD 17
For example, the vertical transfer unit is composed of a two-phase CCD, and in one of the two fields, half the pixels of the photosensitive unit are transferred to one vertical transfer unit by a transfer gate signal, and the next transfer gate signal causes The other half of the pixels are transferred to the other vertical transfer unit.

However, the present invention is not limited to such a two-phase CCD which is read out by interlacing, and it is also possible that all pixels of the photosensitive portion are transferred and read out in a non-interlacing one frame period. In particular, when a memory is provided, the signal read in one frame period can be temporarily stored in the memory and read from the memory in synchronization with the interlaced video signal.

When a memory is provided in the signal processing circuit 45 as shown in FIG. 5, the CCD 17 is driven without being closely related to the display period displayed on the color monitor 5 as in the first embodiment. You can also do it.

For example, the A / D is connected to the output terminal of the amplifier 30 of FIG.
In the case of a configuration in which a converter, a memory having a storage capacity for the total number of pixels of the CCD 17, and a D / A converter are provided, the signal photoelectrically converted by the photosensitive portion of the CCD 17 can be temporarily written in the memory in each field period. It suffices to drive the CCD 17 at such a timing as possible, and the CCD driving method in this case does not need to be closely related to the display period displayed on the color monitor 5. However, the signal read from the memory is closely related to the display period displayed on the color monitor.

For example, after the vertical transfer pulse φV shown in FIG. 3C is output, and after the horizontal transfer pulse φH for one horizontal line pixel number is output as shown in FIG. The drive signal stop period in which the vertical transfer pulse φV is not output is displayed until the horizontal display timing.

In the case of having a memory, immediately after the horizontal transfer pulse φH for one horizontal line pixel is output, the next vertical transfer pulse φV is output, and the drive signal stop period is not provided in this manner. It is possible to drive so as to output the horizontal transfer pulse φH corresponding to the number of pixels of one horizontal line, and the signal output from the CCD 17 can be once written in the memory by this driving.

Also in this case, prior to the timing of outputting the transfer gate pulse φS for transferring the signal charge of the photosensitive portion to the transfer portion, the horizontal transfer pulse φH for at least one horizontal line pixel number is supplied to the horizontal shift register of the CCD 17. By applying the same to the first embodiment, the effect of dark current can be reduced as in the first embodiment.

In the above description, the CCD 17 is explained as an interline transfer type CCD, but the present invention is also applicable to a frame transfer type and line transfer type CCD. Any type of CCD can be similarly applied to a CCD having a horizontal shift register as a horizontal transfer unit.

That is, at least the number of transfer elements in the horizontal direction constituting the horizontal shift register (at least in the horizontal direction) precedes (preferably immediately before) the transfer signal for transferring the signal from the photosensitive section or the transfer section to the horizontal shift register. Pulse train is applied to the horizontal shift register within a short duration of up to several times the number of transfer elements, and remains (remains) in the horizontal shift register due to accumulation (before the original signal is transferred). ) Signal should be swept out.

As described above, strictly speaking, the transfer signal here is a signal for transferring the signal of the photosensitive section or the vertical transfer section to the horizontal shift register. For example, in the first embodiment, the transfer gate pulse φS is added. The vertical transfer pulse φV (that is, φV + φS) or the first vertical transfer pulse φV is applicable. Therefore, also in the first embodiment, when the vertical transfer pulse φV is not output immediately after the output of the transfer gate pulse φS, one horizontal line pixel number to several horizontal line pixel numbers are obtained in the period between these. It is also possible to apply a horizontal transfer pulse train for a minute to the horizontal shift register.

The frame transfer type is almost the same as the interline transfer type CCD, and at least the residual signal (before the original signal is transferred) may be swept out to the horizontal shift register. For example, a pulse train may be applied so as to sweep out the signal remaining in the horizontal shift register before the signal transferred from the photosensitive unit to the vertical transfer unit or before the signal transferred from the vertical transfer unit to the horizontal shift register.

Also in the line transfer type CCD, a pulse train may be applied so as to sweep out the signal remaining in the horizontal shift register before the first vertical transfer pulse for transferring the signal of the photosensitive section to the horizontal shift register.

In this line transfer type CCD, since the photosensitive portion also serves as the vertical transfer portion, the transfer to the horizontal shift register is not performed during the exposure period during which the photosensitive portion is exposed in order to prevent smear. Then, during the light-shielding period after the exposure period, transfer to the horizontal shift register side and signal reading to the outside from the horizontal shift register are performed.

That is, in this CCD, the exposure period is a non-driving period in which no driving signal is output, and the non-driving period (or the driving stop period) is irrespective of the display area of the display means.
Must exist. Also in this case, the effect of dark current can be reduced by applying the pulse train so as to sweep out the signal remaining in the horizontal shift register before the first vertical transfer pulse for transferring the signal of the photosensitive section to the horizontal shift register. Become. In this case, the pulse train for sweeping out may be performed before the end of the exposure period or after the light-shielding period.

Although the means for sweeping out the charges accumulated in the horizontal shift register and accumulated in the non-driving period and causing the dark current is provided in the above-described embodiments, the means for sweeping out the charges in the vertical transfer portion is also provided. You may provide as follows.

For example, in the first embodiment, in FIG. 2D, the switch S2 is short so that a pulse train for driving the horizontal charge storage element (or charge transfer element) of the horizontal shift register about twice can be applied ( Continuation) Period T
1, the switch S2 is turned on before this period T1, and the horizontal transfer pulse φH is supplied to the vertical transfer unit via the switching means (not shown) by the number of elements in the vertical direction. The charges applied and accumulated in the vertical transfer unit are transferred to the horizontal shift register. After transferring all the charges in the vertical transfer section to the horizontal shift register, the switch S1 is turned off.
Then, the switching means (not shown) is switched to return to the normal state, and thereafter, the switch S2 is turned on as shown in FIG. 2 similarly to the first embodiment to transfer the charges from the horizontal shift register and the vertical transfer section. Horizontal transfer pulse φH
You may make it sweep out with.

By doing so, the charges accumulated in the vertical transfer portion during the non-driving period can be removed, and an image less influenced by dark current can be obtained. This driving means or driving method is 1
The vertical transfer is performed in a short period because the drive method that continuously outputs the transfer pulse train (charge sweeping method) is adopted without adopting the drive method that performs horizontal transfer for the number of horizontal elements for each vertical transfer. The charge of the entire part can be swept out.

As a modification of the above, the switch S1 is used.
May be turned on to apply the horizontal transfer pulse φH to the vertical transfer unit to transfer in the horizontal direction, and the switch S2 may also be turned on to apply the horizontal transfer pulse φH to the horizontal shift register to sweep out in the horizontal direction. .

In the above-described embodiment or modification, the horizontal transfer pulse φH is used as the pulse train for sweeping out the charges accumulated in the horizontal shift register, and the pulse train is applied as the pulse train of the number of elements in the horizontal direction or more. However, the present invention is not limited to this, and a generating means for outputting such a pulse train (generally, a higher frequency within an allowable range is better) is provided and the generating means is controlled. Then, before the signals of the photosensitive section or the vertical transfer section are transferred to the horizontal shift register, pulse trains of more than the number of elements in the horizontal direction may be applied.

Incidentally, it is also possible to partially combine the above-mentioned embodiments or modified examples to form different embodiments.
They also belong to the present invention. Although the above description has been mainly described as an example of the solid-state imaging device, the present invention also includes a driving method for driving the solid-state imaging device such as the CCD 17.

[Additional Notes] (1) The solid-state image pickup device is a charge-coupled device, and the light-receiving element portion is composed of a plurality of light-receiving elements arranged two-dimensionally in a horizontal scanning direction and a vertical scanning direction. The horizontal transfer section has a plurality of signal storage elements in the horizontal scanning direction, and sequentially transfers the signals stored by the plurality of signal storage elements in synchronization with a horizontal transfer pulse train and outputs from one end. 2. The solid-state imaging device according to claim 1, wherein a part of the pulse train output by the drive circuit prior to the transfer signal is a part of the horizontal transfer pulse train. (2) The transfer unit has a plurality of signal storage elements in the vertical scanning direction, reads out image information of the plurality of light receiving elements arranged in this direction in synchronization with a transfer signal, and outputs the plurality of signals. The pulse train output from the driving circuit is stored in a storage element, sequentially transferred in synchronization with a vertical transfer pulse train, and has a plurality of vertical transfer units that output the corresponding signal storage devices of the horizontal transfer unit. 2. The solid-state imaging device according to appendix 1, which includes the vertical transfer pulse train.

(3) Upon receiving an output signal from the transfer section of the solid-state image pickup device and converting it into a video signal,
The solid-state imaging device according to claim 1, further comprising a signal processing unit that has a variable input unit, processes an image signal or a video signal based on a variable input from the variable input unit, and outputs the processed video signal. (4) The solid-state imaging device according to claim 1, wherein the solid-state imaging device is provided separately from the drive circuit. (5) The solid-state imaging device according to appendix 3, wherein the signal processing unit includes an external variable input unit to which an external control device that generates the variable is connected.

(6) The solid-state image pickup device has horizontal scanning lines larger than the number of pixels in the horizontal direction of the two-dimensionally arrayed light-receiving elements, receives the output signal output from the solid-state image pickup element, and outputs it. A monitor circuit for displaying as an image; and a drive circuit for outputting a part of the transfer pulse train in a non-image period after the start of the vertical blanking period of the monitor unit and before the generation of the transfer signal. An image display device comprising: the solid-state imaging device according to appendix 1. (7) The image display device according to appendix 6, wherein the continuation of the transfer pulse train ends before the start of the vertical blanking period. (8) The image display device according to appendix 7, wherein the transfer signal and the transfer pulse train are output once during a plurality of vertical scanning periods of the monitor means.

(9) A light receiving element section composed of a plurality of light receiving elements, and output signals of the respective light receiving elements of the light receiving element section are read out to the transfer section in synchronization with the transfer signal, and read out output signals of the respective light receiving elements. In a method for driving a solid-state image sensor having a transfer unit that sequentially outputs the signal to the outside in synchronization with a transfer pulse train, in the solid-state image sensor, the transfer signal generated in a predetermined cycle and a duration shorter than the predetermined cycle. And a driving method of the solid-state imaging device, which is driven by the transfer pulse train that is generated at a time such that a part thereof precedes the transfer signal. The signal remaining in the transfer unit before the transfer signal is applied can be swept out by the transfer pulse train. (10) A light-receiving element portion including a plurality of light-receiving elements that are two-dimensionally arranged in the horizontal scanning direction and the vertical scanning direction, and a plurality of signal storage elements in the horizontal scanning direction, and the plurality of signal storage elements are stored. In the driving of the solid-state imaging device having a horizontal transfer unit that sequentially transfers the signal being output in synchronization with the horizontal transfer pulse train and outputs the transferred signal from one end, a part of the transfer pulse train output prior to the transfer signal is 10. The method for driving a solid-state imaging device according to appendix 9, which is a part of a horizontal transfer pulse train.

(11) A solid-state image pickup device having a light receiving element section composed of a plurality of light receiving elements and a horizontal transfer section for outputting a photoelectric conversion signal photoelectrically converted by each light receiving element of the light receiving element section to the outside, A drive circuit that generates a drive signal including a transfer signal that transfers the photoelectric conversion signal of the light receiving element section to the horizontal transfer section and a transfer pulse that is applied to the horizontal transfer section and outputs the transferred photoelectric conversion signal to the outside. In the non-driving period in which the drive signal is not output immediately before the drive period in which the drive signal is output, a pulse train having a short duration that is equal to or more than the number of horizontal transfer elements forming the horizontal transfer unit is provided in the horizontal transfer unit. And a sweeping-out unit that sweeps out a signal remaining in the horizontal transfer unit before the driving period. The signal accumulated and remaining in the horizontal transfer unit during the non-driving period can be swept out by applying a pulse train having a number of transfer elements in the horizontal direction and a short duration, and the influence of dark current can be prevented by a slight increase in power consumption. .

[0095]

As described above, according to the present invention, the light receiving element portion including a plurality of light receiving elements and the photoelectric conversion signal photoelectrically converted by each light receiving element of the light receiving element portion are transferred and output to the outside. A solid-state image sensor having a transfer section for transferring, a transfer signal for transferring a photoelectric conversion signal of the light receiving element section to the transfer section, and a transfer pulse train for applying the transferred photoelectric conversion signal to the transfer section and outputting the transferred photoelectric conversion signal to the outside. And occur
Precedes the time when the transfer signal is output in a predetermined cycle,
A drive circuit that has a duration shorter than the predetermined period and that outputs a pulse train to the transfer unit at a time such that a part of the predetermined period precedes the transfer signal is provided to configure the solid-state imaging device. Therefore, the electric charge that is accumulated in the transfer unit before the transfer pulse train is applied and is the cause of the dark current is swept out by the pulse train, so that it is possible to generate an image with good image quality and little influence of the dark current. Further, since the pulse train may drive the number of elements in the horizontal scanning direction of the transfer unit, the power consumption by the application of the pulse train is small.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an endoscope apparatus including a first embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the first embodiment.

FIG. 3 is a timing chart diagram for explaining the operation of the first embodiment in a horizontal period.

FIG. 4 is a timing chart diagram for explaining an operation in a modified example of the first embodiment.

FIG. 5 is an overall configuration diagram of an endoscope apparatus including a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a CCD.

FIG. 7 is an operation explanatory diagram of CCD driving in a conventional example.

FIG. 8 is a timing chart diagram for explaining CCD driving in a conventional example at a field rate.

FIG. 9 is a timing chart diagram for explaining CCD driving in a conventional example at a line rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Endoscope device 2 ... Electronic endoscope 3 ... Light source device 4 ... CCU 5 ... Color monitor 6 ... Solid-state imaging device 9 ... Universal cable 10 ... Display part 16 ... Objective lens 17 ... CCD 23 ... Drive circuit 24 ... Signal Processing circuit 25 ... Display area 26 ... CCD drive circuit 27 ... Driver 27a ... φV driver 27b ... φH driver 28 ... Drive control circuit 34 ... Synchronous signal generation circuit S1, S2, S3 ... Switch

Claims (1)

[Claims] 1. A light receiving element portion comprising a plurality of light receiving elements,
A solid-state imaging device having a transfer unit that transfers a photoelectric conversion signal photoelectrically converted by each light receiving element of the light receiving element unit and outputs the photoelectric conversion signal to the outside, and a transfer signal that transfers the photoelectric conversion signal of the light receiving element unit to the transfer unit And a transfer pulse train that is applied to the transfer section and outputs the transferred photoelectric conversion signal to the outside, and precedes the time when the transfer signal is output in a predetermined cycle, and from this predetermined cycle, And a drive circuit that outputs a pulse train to the transfer unit at a time such that a part thereof precedes the transfer signal, and a solid-state imaging device.