JP2770367B2 - Driving method of solid-state imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a solid-state imaging device having an electronic shutter function, and more particularly, to a method for driving a solid-state imaging device in which image unevenness in an electronic shutter mode is reduced. It relates to a driving method.

[Prior Art] FIG. 4 shows a plan view of a conventional example and a solid-state imaging device used in the present invention. As shown in FIG. 1, photosensitive units 1 that perform photoelectric conversion by receiving incident light are provided in a plurality of columns, and each column includes a vertical transfer unit 2 that receives a transfer of photoelectric conversion charges from the photosensitive unit in each column. Are located. At the end of each vertical transfer unit 2, a horizontal transfer unit 3 is provided, and at the output side of the horizontal transfer unit 3, a charge detection unit 4 that converts photoelectrically converted charges into electric signals is provided. On the opposite side of the vertical transfer unit 2 from the horizontal transfer unit 3, a diffusion layer 5 for absorbing extra charges in the shutter mode is provided.

FIG. 5 is a sectional view of the photosensitive section 1 and the vertical transfer section 2 in FIG. As shown in FIG. 1, the photosensitive section 1 and the vertical transfer section 2 are provided on a P-type semiconductor substrate
It is formed in a well 7 sandwiched between channel stops 8. The region of the P well between the photosensitive unit 1 and the vertical transfer unit 2 is a transfer gate unit, and photoelectric conversion charges are transferred from the photosensitive unit 1 to the vertical transfer unit 2 via this region. On the transfer gate unit and the vertical transfer unit 2, a gate electrode 9 for reading out the photoelectric conversion charge to the transfer unit and transferring the same in a direction perpendicular to the paper is formed via an insulating film 10.

FIG. 6 is a potential diagram when a read pulse is applied to the gate electrode 9 in the portion shown in FIG. 5 and when it is not applied.

A conventional driving method of the solid-state imaging device described above will be described with reference to FIG. FIG. 3 is a waveform diagram of drive pulses φ _{V1 to} φ _V4 during a blanking period of a certain field in the electronic shutter mode. In the figure, A is a normal vertical transfer period, B is a period for reading extra charges in the shutter mode, and C is a reverse transfer in which the extra charges are reversely transferred from the vertical transfer unit 2 to the diffusion layer 5 and discharged therefrom. In the period, D is a signal charge reading period, and E is a high-speed vertical transfer period. In the readout periods B to D, charges are read out with pulses φ _V1 and φ _V3 in order to combine charges of two adjacent pixels. In addition, the reason why the electric charges are read out twice from each photosensitive portion in the readout period B is to discharge the surplus electric charges more completely and to prevent the screen from being stained. The reason why the signal transfer period is divided into the high-speed vertical transfer period E and the normal vertical transfer period A is that it is necessary to send out signals of some pixels early depending on a certain imaging mode. If not used, period E is integrated with period A.
In the case of the normal mode other than the electronic shutter mode (1/60 second accumulation mode), the periods B and C are not provided, and this period is included in the period A. In the conventional driving method, the width of the read pulse in the driving pulse, that is, the charge transfer time from the photosensitive section to the vertical transfer section is the same in both the normal mode and the electronic shutter mode.

[Problems to be Solved by the Invention] In the conventional driving method described above, in the electronic shutter mode, image unevenness occurs and image quality deteriorates. If the image unevenness exceeds a certain range, the product must be rejected. Investigation into the cause of the image unevenness revealed that in the shutter mode, the signal waveform of the read pulse became unstable, and the voltage value thereof was reduced. Therefore, even if a readout pulse is applied to the gate electrode during the signal charge readout period D in the shutter mode, the potential shown by the solid line in FIG. 6 cannot be obtained, and becomes the potential shown by the broken line. In addition, the broken lines vary vertically depending on the individual pixels. As a result, the transfer (reading) of the signal charge becomes imperfect, and since this varies depending on the pixel, image unevenness appears on the screen.

Therefore, two measures for increasing the voltage of the read pulse and increasing the transfer (read) time can be considered as measures for ensuring the transfer of the signal charge. But,
If the former measure is adopted, the possibility of defects appearing on a part of the screen due to variations during device manufacturing increases, and if the latter measure is adopted, the transfer time in both the normal mode and the electronic shutter mode is reduced. If it is longer, the smear component increases in the normal mode, and the image quality deteriorates.

Means for Solving the Problems The present invention provides a plurality of photosensitive units for photoelectrically converting incident signal light, and a transfer unit for receiving the transfer of photoelectrically converted charges in parallel from the plurality of photosensitive units and transferring the same. And a charge detection unit that receives the photoelectric conversion charge from the transfer unit and converts the charge into an electric signal, and transfers the photoelectric conversion charge from the photosensitive unit to the transfer unit. The transfer time for the electronic shutter mode is longer than that for the normal mode.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a waveform diagram of a driving pulse showing one embodiment of the present invention, and FIG. 2 is an enlarged view of a signal readout portion thereof.

FIG. 1 is a waveform diagram in a blanking period, as in FIG. 3, and the periods A to E are the same as those in FIG. In FIGS. 1 and 2, the solid line indicates the read pulse in the electronic shutter mode and the broken line indicates the read pulse in the normal mode in the signal read period D.

As is apparent from these figures, in the present invention,
The signal transfer time in the electronic shutter mode is longer than in the normal mode.
In this way, even in the shutter mode, even if the voltage of the read pulse decreases as shown by the broken line in FIG. 6, or if the voltage fluctuates, the signal charges in the photosensitive section are almost completely transferred to the vertical transfer section. Can be transferred to More specifically, if the reading time in the shutter mode is 5 μs when the reading time in the normal mode is 2 μs, it is possible to read out the charge of the photosensitive portion almost completely.

According to this method, since the voltage of the read pulse is not increased, no defect appears on the screen based on manufacturing variations, and the transfer time is not lengthened in the normal mode. There is no increase in smear in the normal mode.

[Effects of the Invention] As described above, according to the present invention, the transfer time from the photosensitive unit to the vertical transfer unit in the electronic shutter mode is made longer than in the normal mode, and therefore, according to the present invention, In the shutter mode, charges can be almost completely transferred from the photosensitive section to the vertical transfer section without sacrificing other characteristics. Therefore, according to the present invention, it is possible to prevent image unevenness that may occur due to manufacturing variations, and as a result, it is possible to improve product yield.

[Brief description of the drawings]

FIG. 1 is a drive pulse waveform diagram showing one embodiment of the present invention,
2 is a partially enlarged view of FIG. 1, FIG. 3 is a waveform diagram of a driving pulse of a conventional example, FIG. 4 is a plan view of a solid-state imaging device,
FIG. 5 is a partial sectional view of FIG. 4, and FIG. 6 is a potential diagram of the portion of FIG. 1 photosensitive section 2 vertical transfer section 3 horizontal transfer section
4 ... Charge detecting unit, 5 ... Diffusion layer, 6 ... N-type semiconductor substrate, 7 ... P well, 8 ... Channel stop, 9 ...
Gate electrode 10, insulating layer, φ _{V1 to} φ _V4, drive pulse, A, normal vertical transfer period, B, extra charge readout period, C, reverse transfer period, D, signal charge readout period, E: High-speed vertical transfer period.

Claims (1)

(57) [Claims] 1. A plurality of photosensitive units for photoelectrically converting incident signal light, a transfer unit for receiving and transferring photoelectrically converted charges in parallel from the plurality of photosensitive units, and a photoelectrically converted charge from the transfer unit. And a charge detection unit for converting the charge into an electric signal, wherein the transfer time for transferring the photoelectric conversion charge from the photosensitive unit to the transfer unit is longer in the electronic shutter mode than in the normal mode. The method of driving a solid-state imaging device, wherein the method of (1) is longer.