JPH02135986A - Image pickup element driving circuit - Google Patents

Abstract

PURPOSE:To prevent a flicker by forcibly making the storage time of an image pickup element coincide with the fluctuation cycle of a light source when it is detected that the light source fluctuates by using that light quantity for each screen can be kept constant when the fluctuation cycle of the light source and the storage time of the image pickup element coincide with each other. CONSTITUTION:Since an output signal from a photodiode 2 changes according to the light quantity, the output signal is passed through an AGC(automatic gain control) circuit 3 and amplified so that the signal level of the output signal can be kept constant, and only the fluctuation component of the output signal is taken out in a BPF (band-pass filter) 4. One obtained fluctuation signal component is amplified in an amplifier 5 and sent to a counter 6, the frequency of the component is measured, and the measured frequency is informed to a controller 9. Further, for the output of the BPF 4, its full waves are rectified, and its amplitude level is converted into a DC potential in a rectifier 7, afterwards, the output is sent to a comparator 8. Further, when the output is a small fluctuation component (including noise), its operation is inhibited by the comparator 8. Thus, the storage time timing of an image pickup element 12 is made to coincide with the fluctuation cycle by a driving part 11, and the flicker can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image sensor drive circuit that performs photoelectric conversion, and particularly to a drive circuit for a solid-state image sensor for a video camera.

[Conventional technology]

Traditionally, the solid-state image sensor (area image sensor) used in video cameras was fixed to the vertical synchronization signal of the TV, but in recent years, so-called Video cameras with a variable shutter function are on the rise.

[Problem to be solved by the invention]

However, this conventional variable shutter function has no problem with subjects where the amount of light is constant over the storage time of the image sensor, such as sunlight, but when the amount of light changes over time, such as with fluorescent lights. When such a light source is used, the amount of light for each screen changes depending on the storage time of the image sensor, and as a result, a flicker appears in the recorded image, resulting in a so-called flicker phenomenon.

For example, in the Kanto area, the frequency of AC 100V power supply is 5
Since it is 0Hz, the period is 20m5. The amount of light changes repeatedly in 10 m5, but if this is captured using a shutter mode of 1/1000 seconds, the accumulation time will be 1 ms. Since the video signal of the video camera and the power supply are asynchronous, the slow brightness changes of the fluorescent lamp of 10 m5 cycles can be controlled in a short period of 1 ms during the vertical synchronization signal period of the television (approximately 16.5 m in NTSC).
Since one screen's worth of data is accumulated every 7 m5), it is clear that the amount of light for each screen differs.

The purpose of the present invention is to solve such problems and to solve the problem by using the fact that the amount of light for each screen can be kept constant if the fluctuation period of the light source matches the storage time of the image sensor. An object of the present invention is to provide an image sensor driving circuit which prevents flickering by forcibly adjusting the storage time of an image sensor to match the fluctuation cycle when it detects that the image sensor is changing.

[Means to solve the problem]

The configuration of the image sensor driving circuit of the present invention includes: an image sensor capable of controlling the accumulation time of a photoelectrically converted optical signal; a fluctuation frequency detection means for detecting a light intensity fluctuation frequency of a light source received by the image sensor; The apparatus is characterized by comprising a drive circuit that controls the storage time of the image pickup element in accordance with the output of the fluctuation frequency detection means so as to cancel out the fluctuation period.

〔Example〕 Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. first,
Light from the subject 15 passes through the lens 13 and enters the image sensor 12.
At the same time, it is also input to the photodiode 2 through the diffuser plate 1. Since the output signal from this photodiode 2 changes depending on the amount of light, AGC (automatic gain control)
The signal is amplified through circuit 3 to a constant signal level.

Then, the output is passed through a BPF (band pass filter) 4 to extract only the fluctuation component of the light amount. The reason why this BPF4 cuts the high frequency side is that, for example, the maximum shutter operation speed is about 1/1000 seconds = 1ms).
, 1 ms or less to 10 KHz or more, and flicker does not occur for light that fluctuates sufficiently quickly, such as from a high-frequency lighting type fluorescent lamp.

One of the fluctuating signal components thus obtained is amplified by an amplifier 5, sent to a counter 6, whose frequency is measured, and the controller 9 is notified. Also, the output of BPF5 is the rectifier 7
The signal is full-wave rectified and the amplitude level is converted to a DC potential, which is sent to the comparator 6. In other words, the total amount of incident light is A
Since the level is set at a constant level by the GC circuit 3, the magnitude of the fluctuation component in the level of the incident light amount is obtained by rectifying the level, so this is set by the comparator 6 and the resistor 10. Compared to the level, the operation is prohibited for small fluctuation components (including noise) below that level. That is, the controller 9 including the microcomputer matches the fluctuation period of the accumulation time timing of the image sensor 11 with the driving section 11 according to the fluctuation frequency component information of a predetermined value or more, thereby preventing the occurrence of flicker.

〔Effect of the invention〕

As described above, the present invention has the effect of making it possible to prevent the occurrence of flicker by making the signal accumulation time of the image sensor coincide with the fluctuation period by detecting the fluctuation in the light amount of the subject.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention. 1... Diffusion plate, 2... Photodiode, 3... A
GC circuit, 4... BPF, 5... amplifier, 6...
Counter, 7... Rectifier, 8... Comparator, 9
...Controller, 10...Resistor, 11...Driver, 12...Image sensor, 13...Lens.

Claims (1)

[Claims] an image sensor capable of controlling the accumulation time of a photoelectrically converted optical signal; a variable frequency detecting means for detecting a frequency of variation in the amount of light from a light source received by the image sensor; 1. An image sensor drive circuit comprising: a drive circuit that controls the accumulation time of the image sensor so as to cancel out its fluctuation cycle.