JPH037482A - Drive method for solid-state image pickup element - Google Patents

Abstract

PURPOSE:To reduce the time required to read a signal charge by driving a vertical transfer section continuously so as to drive a memory section intermit tently for each horizontal scanning period when the signal charge generated in a photodetector section is transferred to the memory section at a high speed via the vertical transfer section. CONSTITUTION:When the transfer of memory sections 5a-5c and the addition of signal charges are repeated for one period each (one line operation, one line stop) while vertical transfer sections 2a-2c apply continuous transfer, the signal charge is added by 2-picture element each. When it is observed from the standpoint of the solid-state image pickup element, the signals are added by vertical 2-line each and when the signal charge of the vertical transfer sections 2a-2c is finished entirely through the transfer as above, the memory sections 5a-5c are only filled a half. Then the pickup is repeated once more and similar transfer is applied to occupy the memory sections 5a-5c fully. When the charge is read, signals by 2 patterns are read for one vertical scanning period. Thus, the readout time per one pattern is reduced and the time for AF, AE is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for driving a solid-state image sensor, and more particularly to a method for driving a solid-state image sensor suitable for AE and AF operations.

(Background of the Invention) In a camera that captures an image using a solid-state image sensor such as a CCD, AE (automatic exposure adjustment), which is performed before capturing an image,
Some devices perform AF (autofocus) using an output signal from a solid-state image sensor.

For example, the output of a CCD that has been exposed under certain exposure conditions is read out, and the output signal is integrated.

Then, a feedback loop is repeated so that the integrated signal becomes an appropriate value, and appropriate exposure conditions are obtained.

In the case of AF, an image is captured, the output of the CCD is read out, a high frequency component in the signal is extracted, and its magnitude is determined. Then, move the lens to capture and read the image again.
Repeat high frequency component extraction.

This is performed at each lens position, and the position where the high frequency component is maximum is determined to be in focus.

Conventional general solid-state image sensor (hereinafter referred to as CCD)
Examples include interline CCDs (IT-CCDs) and frame interline CCDs (FIT-CCDs).

The FIT-CCD has a memory section between the vertical transfer section and the horizontal transfer section, and the charge transferred from the light receiving section to the vertical transfer section is shifted to the memory section at high speed (this is called high-speed transfer). . Then, shift vertically from the memory section,
The voltage is read out from the horizontal transfer section via a read amplifier to the outside as a voltage corresponding to the signal charge.

(Problem to be Solved by the Invention) Incidentally, when performing AE or AF, it is often necessary to use only a signal at the center of the screen. However, the image signal is read out by scanning according to a standard method. Therefore, even in such a case, reading is started sequentially starting from, for example, the pixels on the left side of the screen, so a waiting time occurs for portions unrelated to AE and AF.

This results in wasted time, which prevents speeding up of AE and AF.

However, in order to read out the CCD output signal only in the area where AF or AE is performed on the screen, it is necessary to
There is a problem that the drive circuit needs to be modified, and the circuit configuration and drive method become complicated.

The present invention has been made in view of the above problems, and its purpose is to realize a method for driving a solid-state image sensor suitable for AE and AF operations.

(Means for Solving the Problems) A method of the present invention for solving the above problems is a method for vertically transferring signal charges generated in a light receiving part in a method of driving a solid-state image sensor having a light receiving part, a vertical transfer part, and a memory part. When performing high-speed transfer to the memory section via the memory section, the vertical transfer section is continuously driven, and the memory section is intermittently driven at every horizontal scanning period.

(Function) In the method for driving a solid-state image sensor of the present invention, when the signal charges generated in the light receiving section are transferred at high speed to the memory section via the vertical transfer section, the vertical transfer section is continuously driven and the memory section is transferred to the memory section. It is driven intermittently every horizontal scanning period. Therefore, the signal charges from the vertical transfer section are transferred while being added in the memory section.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an example of a configuration for implementing the method of the present invention (F
FIG. 2 is a configuration diagram showing an IT-CCD.

In this figure, reference numeral 1 denotes a light receiving section that generates charges according to the amount of received light. Here, the case of 3×4 pixels is shown, and 1a
-III are light-receiving elements constituting a light-receiving section, respectively.

Did 28~2C occur at the light receiving part? This is a vertical transfer unit that transfers one load vertically.

Reference numerals 58 to 5c are memory sections for storing charges from the vertical transfer sections 2a to 2c. 3 is a horizontal transfer section for horizontally transferring charges from the memory sections 5a to 5c, and 4 is a read amplifier for converting the charges transferred from the horizontal transfer section 3 into a voltage and reading it out to the outside.

FIG. 2 is an explanatory diagram showing the state of charge potential during charge transfer of the above-mentioned solid-state image sensor.

Here, charge transfer in the vertical direction (vertical transfer section - memory section) is shown.

The operation of this embodiment will be explained below using these figures.

In the F fT-CCD shown in this figure, vertical transfer section 2 (2
The memory section 5 (5a-2c) is located between the horizontal transfer section 3 and the horizontal transfer section 3.
5c), and shifts the charges transferred from the light receiving section 1 to the vertical transfer section 2 to the memory section at high speed (generally referred to as high-speed transfer). Then, the data is sequentially shifted vertically from the memory section 5 and read out from the horizontal transfer section 3 via the read amplifier 4.

FIG. 2 (9) to (17) show the state during normal FIT-COD high-speed transfer. By repeating this, the light receiving section 1. All signal charges in the vertical transfer section 2 are sent to the memory section 5.

In this embodiment, normal high-speed transfer (Fig. 2 (9) to (17))
) New charge transfer (Fig. 2 (1) to (9),
It is characterized by performing (17) to). Furthermore, the second
From Figure (17) onwards, the process from (1) onwards is repeated.

That is, the charges in the vertical transfer section 2 are moved during the period when the charges in the memory section 5 are stopped. This results in
New charges from the vertical transfer section 2 are added to the charges already existing in the memory section 5 (see Figure 2 (5)).

(6), (7)).

In this way, while the vertical transfer section 2 is continuously transferring, if the transfer of the memory section 5 and the addition of signal charges are repeated one cycle at a time (one line operation, one line stopped), the signal Charges will be added for two pixels at a time.

When looking at this for the entire solid-state image sensor, it is an addition of two lines in the vertical direction. When such a transfer is performed, when all the signal charges in the vertical transfer section 2 have been transferred, the memory section 5
This means that it is only half full. So, already-
By repeating imaging and performing similar transfer, the memory section 5 is completely filled. When this is read out, signals for two screens can be read out in one vertical scanning period. That is, the readout time per screen is shortened, and the time required for AF and AE can be shortened. However, since the addition is performed two lines at a time, it is not complete image information, but it is sufficient for AF and AE that use imaging signals.

In the above example, the transfer of the memory unit 5 is a one-line operation.

This is the case of 1 line stop and 2, but other operations are also possible. That is, it is also possible to perform operation for one line and stop for n lines, and to perform addition for each n+1 line. However, in the case of two-line operation, one-line stop, etc., the magnitude of the signal charge differs from line to line, making it difficult to handle.

Furthermore, when the number of lines to be added increases, signal charges may overflow in the memory section 5. In such a case, in advance,
It is desirable to increase the capacity of the memory section 5 or to provide an overflow drain (CCFD) at the first electrode section of the memory section 5.

Ordinary solid-state image sensing devices can also operate in field accumulation mode, so the signal charges added for each two pixels are sent to the transfer section without overflowing.

Therefore, if the frame accumulation mode is operated and the drive method of this embodiment is used to add two lines at a time during high-speed transfer, there is no fear of signal charges overflowing.

Furthermore, in this embodiment, since addition is performed for each n line, this corresponds to increasing the sensitivity by n times. That is, compared to obtaining a similar signal level in normal operation, the exposure time can be reduced to 1/n.

In AE and AF using imaging signals, optimal conditions are determined by repeatedly capturing images under various conditions. Therefore, according to this embodiment, in addition to shortening the readout time, there is also the effect of shortening the exposure time due to increased sensitivity, and the AE and A
This greatly contributes to improving the processing speed of F.

(Effects of the Invention) As described in detail above, in the present invention, when transferring signal charges generated in the light receiving section to the memory section via the vertical transfer section at high speed, the vertical transfer section is continuously driven and , the memory section is driven intermittently every horizontal scanning period.

Therefore, the signal charges from the vertical transfer section are transferred while being added in the memory section. Therefore, the time required to read signal charges is shortened, and a method for driving a solid-state image sensor suitable for AE and AF can be realized.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a configuration for implementing the method of the present invention, and FIG. 2 is an explanatory diagram for explaining potential changes during charge transfer. 1a to 1g... Light receiving section 2a to 2c... Vertical transfer section 3... Horizontal transfer section 4... Readout amplifier 5
...Memory part

Claims (1)

[Claims] In a method for driving a solid-state image sensor including a light receiving section, a vertical transfer section, and a memory section, when signal charges generated in the light receiving section are transferred at high speed to the memory section via the vertical transfer section, 1. A method for driving a solid-state image sensor, comprising continuously driving a vertical transfer section and driving a memory section intermittently at every horizontal scanning period.