JPH0435280A - Image pickup element driver - Google Patents

Abstract

PURPOSE:To suppress noise due to a dark current by providing an image pickup element driving circuit which drives an image pickup element by charge pumping until a diaphragm is closed after an object is photographed. CONSTITUTION:A CCD (image pickup element) 3 generates a video signal in accordance with the image of the object, and it is outputted to a video signal processing circuit 6. Thence, a control circuit 8 drives an electric charge read out to the CCD 3 by charge pumping by controlling a driving circuit 5. In other words, an electron hole can be captured by boundary trap phenomenon in the neighborhood of oxide film of SiO2 of the CCD 3 by repeating a charge pumping operation, while, the maximum dark currents occur in the neighborhood of the oxide film. As a result, the dark current is coupled with the electron hole, then, disappears. In such a way, a dark current component can be suppressed by driving the image pickup element by charge pumping in a period until the diaphragm is closed after performing photographing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image sensor driving device suitable for application to an electronic digital camera.

[Prior Art] When a subject is photographed in an electronic still video camera, a video signal of the subject is output from an image sensor such as a CCD, and this video signal is recorded on a video floppy.

By the way, if the signal captured by the image sensor is not read out while light is incident on the sensor element, smear etc. will occur, which is undesirable. Reading from the image sensor and removing smear etc.
The applicant previously proposed this in Japanese Patent Application No. 1983-317004.

[Problems to be Solved by the Invention] However, since the previously proposed device reads out the image fl (, No. 17) after the diaphragm is closed, the period until the diaphragm is closed is However, there was a problem in that dark current was generated, and in the worst case, white scratch-like noise appeared on the screen.

Dark current has a temperature dependence, so if the temperature of the image sensor itself and its surroundings is not high, it will not be so bad, but in the monitor mode where the IM image element is continuously driven, the n-image element and peripheral circuits will generate heat. and the temperature rises. When recording in such a state, noise such as white scratches due to dark current becomes noticeable.

The present invention was developed in view of this situation, and is intended to suppress noise caused by dark current.

[Means for Solving the Problems] An image sensor driving device of the present invention includes an image sensor that outputs a video signal corresponding to an image of a subject, an aperture that controls exposure of the image sensor, and an aperture drive circuit that drives the aperture. and an 1118-element drive circuit that charges-bumps the image sensor until the aperture is closed after photographing the subject.

[Function] In the image sensor driving device configured as described above, the image sensor can be driven by charge bombing during a period after imaging and before being read out.

Therefore, it is possible to prevent the occurrence of smear and to suppress noise due to dark current.

Embodiment 1 FIG. 1 is a block diagram showing the configuration of an embodiment of an image sensor driving device of the present invention.

Light emitted from a subject (not shown) is incident on a CCD 3 (imaging device) via a photographic lens l and an aperture 2. C.C.
D3 generates a video signal corresponding to the image of the subject, and outputs the video (
It is output to the No. 8 processing circuit 6. The video signal processed in the video signal processing circuit 6 and subjected to FM modulation is input to the magnetic disk device 7 and recorded on a video floppy (not shown).

Control circuit 8 consisting of a microcomputer (MPU), etc.
drives the photometric element 9 via the drive circuit V810 to perform a photometric operation. The drive circuit 4.corresponds to the photometry result.
The diaphragm 2 and the CCD 3 are each driven through the lens 5. 1
Reference numeral 1 denotes a release switch that is operated when photographing.

Next, the operation will be explained with reference to the timing chart of FIG.

When the release switch 11 is pressed halfway, the control circuit 8 drives the photometric element 9 via the drive circuit 10 to photometer the exposure state of the subject. The control circuit 8 calculates the amount of cod stock from the output of the photometric element 9.

When the release switch 11 changes from a half-pressed state to a fully-pressed state (FIG. 2A), the control circuit 8 controls the drive circuit 4 in accordance with the calculation result to open the aperture 2 (FIG. 2B). ). As a result, the light incident from the photographing lens 1 is adjusted to an appropriate amount by the diaphragm 2, and then enters the CCD 3.

The control circuit 8 controls the drive circuit 5 and supplies the CCD 3 with four-phase vertical drive signals φv1 to φV4 (second figures to G) synchronized with the vertical synchronization signal (FIG. 2 C) and the horizontal synchronization signal, as well as the horizontal drive signal. supply. Hereinafter, φv1 to φv4 will be simply referred to as drive signals.

Microscopically, as shown in Figure 3, the CCD 3 consists of a light-receiving section consisting of photodiodes PD arranged in a matrix, a vertical CCD section that vertically transfers the charges generated by this light-receiving section, and a horizontal CCD section. It consists of a horizontal CCD unit that transfers data to

Since the vertical CCD section is driven in four phases, four electrodes (V1 to V4) are repeatedly provided in the vertical direction.

A photodiode is connected to rM, 4'f3V1 and v3 through a transfer gate (TG) section, respectively.

By controlling the voltage value and phase of the drive signals applied to the voltages 11iV1 to 11iV4, the charges of each photodiode can be read out to the CCD and the read charges can be roughly transferred.

At a predetermined timing, as drive signals φv1 and φv3,
A TG pulse is applied. As a result, the charge that had been generated in the potdiode PD is successively discharged to the vertical CCD. The charges read out to the vertical CCDs are transferred and discarded by high-speed pulses applied as drive signals φv1 to φ■4.

When time Tv has elapsed after the first T G pulse,
A second I'G pulse is generated. This time 'r'
v is calculated W corresponding to the 6111 light result.

That is, during the time TvO! - The charges generated in the PD are read out to the vertical CCD section at the timing of the second 1'G pulse. Then, diaphragm 2 closes,
Vertical drive is stopped until recording gate No. 13 is cleared.

Next, the control circuit 8 controls the drive frequency V85 and drives the charge continuously delivered to the CCD by charge bombing until the diaphragm 2 is closed.

This charge bombing operation will be briefly explained.

That is, the drive circuit 5 outputs the drive signals φ■1 to φV4 (
7) Change the level from time Ll to t5 as shown in Fig. 4(b).
), it changes from moment to moment.

As a result, as shown in FIG. 4(a), at time t1, the charges A and B held in CCDVI and V2 are
F, at time L2, it is spread to CCDV1 to V3. Moreover, at time L3, this charge is CCDV2
and v3, and at time t4, Kibi, C
It is spread to CDV1 to v3.

Thereafter, similarly, the operation of transferring and returning charges within a relatively short distance is repeated. If this operation is explained below one electrode, since a charge pumping effect occurs (in this case, from Vl to V3), it is called charge pumping drive.

When the charge pumping operation is repeated in this way, holes are trapped near the 5 in 2 oxide film of the CCD due to the interface trap phenomenon, as shown in FIG. on the other hand,
Dark current occurs most often near this oxide film. As a result, this dark current combines with holes and disappears.

The charge bombing drive is repeated until the diaphragm 2 is closed.

After the aperture 2 is closed, the control circuit 8 outputs the recording gate signal (
FIG. 2 []) is generated, the drive circuit 5 is driven, and the CCD3
transfer the signal charges held in the vertical CCD section of the
Not read as a video signal. The video signal processed in the video signal circuit 6 is supplied to a magnetic disk device 7 and recorded on a video floppy.

[Effects of the Invention] As described above, according to the image sensor driving device of the present invention, the image sensor is charge-bumped driven during the period after imaging until the aperture is closed, so that the 114 current component is suppressed. can do.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the image sensor driving device of the present invention, FIG. 2 is a timing chart illustrating the operation of the embodiment of FIG. 1, and FIG. 3 is a diagram similar to the one shown in FIG. FIG. 4 is a detailed plan view of the CCD, FIG. 4 is a timing diagram for explaining the di-bombing operation, and FIG. 5 is a diagram for explaining the relationship between the structure of the CCD and the potential. 1...Photographing lens, 2...Aperture, 3...CCD, 4
゜5.10・Drive circuit, 6...Image (9 Tsukuda circuit, 7・
...Magnetic disk device, 8.Control circuit, 9.Photometering element,■.--Release switch. Patent applicant Asahi Optical Co., Ltd.

Claims (1)

[Scope of Claims] An image sensor that outputs a video signal corresponding to an image of a subject; an aperture that controls exposure of the image sensor; an aperture drive circuit that drives the aperture; An image sensor driving device comprising: an image sensor drive circuit that drives the image sensor by charge pumping until an aperture is closed.