JPH0815324B2 - Solid-state imaging device for TV - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a solid-state image pickup device for a television, and more particularly to a solid-state image pickup device for a television which eliminates a flicker phenomenon caused by the asynchronous scanning cycle and lighting lighting frequency. It is a thing.

[Conventional technology]

Along with the great development of solid-state device technology centered on integrated circuits, solid-state imaging devices are rapidly advancing. The solid-state imaging device also requires three basic functions of photoelectric conversion, storage, and scanning, but scanning does not use an electron beam like an image pickup tube, but sends a pulse in a circuit to independently form a mosaic. The selected pixels are switched one after another. Since the pixel arrangement is fixed and the pulse sending time is controlled by the clock as described above, the distortion of the figure is very small except the distortion caused by the optical system. Therefore, it is advantageous for applications requiring geometrical accuracy such as measurement and figure recognition. In addition, the solid-state imaging device is housed in an IC package, and is characterized by its small size, light weight, robustness, vibration resistance, low power consumption, and reliability.

Since such a conventional solid-state image pickup device complies with the NTSC standard television system, especially in Japan, the scanning of the solid-state image pickup device is performed at a 1/60 second cycle. In that case, in the conventional MOS type solid-state imaging device, interline type CCD (charge coupled device) or frame transfer type CCD, the accumulation period was 1/60 seconds or 1/30 seconds. On the other hand, in the Kanto region, since the power supply frequency is 50 Hz, the lighting cycle of the lighting (especially the fluorescent lamp) and the scanning cycle of the solid-state image sensor are not synchronized, so that 20 Hz flicker occurs. This flicker phenomenon is a very noticeable phenomenon on the reproduction screen, and the more the improvement in the afterimage characteristic of the solid-state image pickup element is caused, the more flicker becomes conspicuous.

However, in recent years, a solid-state image sensor has been developed in which the signal storage time can be freely changed within the range of 1/60 to 1/15750 seconds.
A typical structure example of such a solid-state imaging device is shown in FIGS. 6 and 7.

The one shown in FIG. 6 is a MOS type solid-state image pickup device with a variable storage time. This solid-state image pickup device has two vertical registers, a vertical shift register 100 for sweeping and a vertical shift register 101 for reading. The feature is that the excess signal sweeping scanning is performed prior to the signal reading scanning. By this preceding scan, each photodiode 102
Is reset once before the signal is read out and the signal (charge) is restored
Start accumulating. Therefore, the effective accumulation time related to the element output is the time from the time when the accumulation is started again until the reading, that is, the phase difference between both scans. This phase difference becomes variable by mutually changing the timings of the start pulses of the two vertical shift registers 100 and 101. Therefore, according to this solid-state image sensor, one horizontal scanning period t _H
It is possible to easily change the accumulation time in units of.

FIG. 7 shows a CCD type solid-state image sensor with a variable storage time CCD having a structure called a FIT (frame interline transfer) CCD, and FIG. 8 shows the timing for varying the storage time using the FIT CCD. Indicates. In the CCD of this FIT structure, the photodiode 110 of the image pickup unit is provided during the horizontal blanking period.
The unnecessary charges are transferred from the vertical CCD 111 to the vertical CCD 111, and the signal charges are stored. During this time, the unnecessary charges transferred to the vertical CCD 111 of the image pickup section are swept out to the drain section 113 using the blanking period and the vertical blanking period. After the constant signal accumulation period T3, the signal charges of the photodiode 110 are transferred to the vertical CCD 111 of the image pickup unit, and are frame-transferred to the accumulation unit 112 in the period T2. The signal charge transferred to the storage unit 112 is 1
Each line is transferred to the read register 114 and sequentially read out. Therefore, even when the CCD having such a structure is used, the accumulation period can be arbitrarily changed in steps of one horizontal period.

It is possible to eliminate the flicker phenomenon in the 50 Hz region by using a solid-state image sensor having a structure capable of controlling the accumulation period. That is, as shown in FIG. 9, if the accumulation time of the solid-state image sensor is set to 1/100 second, even if the fluorescent lamp is turned on at 50 Hz, the shaded area in this figure indicates during the accumulation period. The amount of light integrated into is constant in any field. This makes it possible to eliminate flicker in areas where the power supply frequency is 50 Hz.

[Problems to be solved by the invention]

However, by setting the storage time to 1/100 second in this way, flicker can be removed in the area where the power supply frequency is 50 Hz, but conversely, even in the 60 Hz area where there is no problem of flicker, the storage time is reduced to 1/100 seconds. 100 seconds, 1/60
Even if there is no problem even in the second storage period, the sensitivity will be reduced by shortening the storage time. However, providing a manual switch for switching the accumulation time only complicates scanning, and there is a practical problem such as forgetting to turn on the switch.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a solid-state image pickup device for a television capable of eliminating the occurrence of a flicker phenomenon and maintaining high sensitivity without complicating the operation.

[Means for solving problems]

In order to achieve such an object, the present invention provides a solid-state image sensor whose signal storage time is variable according to the timing of a drive signal, and a lighting frequency of a lighting unit which illuminates an object imaged by the solid-state image sensor is the solid-state image sensor. In order to detect whether or not it is synchronized with the scanning frequency of 1st, a signal corresponding to the brightness of the subject is detected for each vertical scanning cycle, and the detection outputs for each vertical scanning cycle are compared with each other.
And a second comparison calculation means (12) for comparing the output from the comparison calculation means with a predetermined reference value,
The accumulation time of the solid-state image pickup device is set as the lighting period of the illumination means so that flicker does not occur when it is detected by the output of the second comparison operation means that the asynchronous component is equal to or higher than a predetermined level, and the asynchronous component is When it is detected that the amount is less than a predetermined level, the switching time is switched to increase the sensitivity by setting the accumulation time of the solid-state image sensor to the vertical scanning period.

[Operation] According to the present invention, with the above configuration, the detecting means automatically detects whether or not the lighting frequency of the illuminating means is in synchronization with the scanning frequency of the solid-state image pickup device at every vertical scanning cycle, and detects that it is asynchronous. In this case, the accumulation time of the solid-state image sensor is set as the lighting period of the illumination means so that flicker does not occur, and when the synchronization is detected, the accumulation time of the solid-state image sensor is set as the vertical scanning period. Since the switching means automatically switches to increase the sensitivity, it is possible to eliminate the occurrence of the flicker phenomenon and maintain the high sensitivity without complicating the scanning, and it is possible to achieve optimum imaging. it can.

That is, in the present invention, for example, in the case of the NTSC standard television system, if a flicker based on a fluorescent lamp driven by a commercial AC frequency of 50 Hz is detected, the lighting frequency in the case of a commercial frequency of nHz is 2nHn. The accumulation time of the solid-state image sensor is set to 1/100 second. For example, when the commercial frequency and the scanning frequency are synchronized (when the commercial frequency is 60 Hz) even outdoors or under fluorescent light, Since the switching is made so that the accumulation time is 1/60, 50Hz
Flicker in the area is eliminated and high sensitivity is maintained in the 60Hz area. Similarly, in the present invention, in the case of the PAL / SECAM system, the storage time is automatically switched to 1/50 second at a commercial frequency of 50 Hz and 1/120 second at a commercial frequency of 60 Hz.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the basic configuration of the embodiment of the present invention. In the figure, a is a solid-state image sensor, and the signal storage time is variable depending on the timing of the drive signal. b is a detection means,
It is detected whether or not the lighting frequency of the illumination means d for illuminating the object imaged by the solid-state image sensor a is synchronized with the scanning cycle of the solid-state image sensor a. Reference numeral c is a switching means, and the accumulation time of the solid-state image pickup device a is set as a lighting cycle of the lighting means d so that flicker does not occur when the detection means detects that it is asynchronous, and the switching means is synchronized. When it is detected, the accumulation time of the solid-state image sensor a is set to a vertical period based on the scanning cycle to switch the sensitivity so as to increase the sensitivity.

FIG. 2 shows the circuit configuration of an embodiment of the present invention. In this figure, 1 is a lens for forming an image of a subject, 2 is a diaphragm for adjusting the amount of incident light, 3 is a solid-state image pickup device of variable storage time as shown in FIG. 6 or 7, and 4 is solid-state image pickup. A drive circuit 5 for driving the element 3 is a timing generation circuit for generating drive timing of the drive circuit 4. A signal processing circuit 6 processes the output signal of the solid-state image sensor 3 and outputs a video signal.

Reference numeral 7 is an integrating circuit for integrating the output signal of the solid-state image pickup device 3 for one vertical scanning period, and reference numeral 8 is an auto iris circuit for controlling the diaphragm 2 so that the output of the integrating circuit 7 is always constant. twenty two
Is an A / D conversion circuit for A / D (analog / digital) converting the output of the integration circuit 7, and 9 is a memory for storing the integrated value converted into a digital value by the A / D conversion circuit 22 for each vertical scanning period. , 10 is a subtraction circuit that takes the difference between the integrated value of the current field obtained directly from the A / D conversion circuit 22 and the integrated value of the previous field stored in the memory 9, and 11 is the output of the subtraction circuit 11.
An integrating circuit for integrating every vertical scanning period, and a comparing circuit 12 for comparing the output of the integrating circuit 11 with a reference value of a predetermined reference value generating circuit 13. Reference numeral 14 is a timer circuit that gives a time limit to the operation of the comparison circuit 12, 15 is a power supply circuit that supplies power to the timer circuit 14 and the timing generation circuit 5, and 16 is a power switch that opens and closes the power supply circuit 15.

Next, the operation of this embodiment shown in FIG. 2 will be described. In the above configuration, when the power switch 16 is turned on, power is supplied to the entire imaging device, and the timer circuit 14 is turned on after waiting for the circuit to stabilize, and the comparison circuit 12
The comparison operation of is started. The accumulation time of the solid-state image sensor 3 is set to a short time of about 1/1000 second at the time of closing.

The output of the solid-state image sensor 3 is integrated by the integration circuit 7 for one vertical scanning period. The output of the integrating circuit 7 is sent to the auto iris circuit 8, and the diaphragm 2 is controlled by the control signal of the auto iris circuit 8 so that the output of the integrating circuit 7 is always constant.

The integration result of the integrating circuit 7 within one vertical scanning period is converted into a digital value by the A / D converting circuit 22 and stored in the memory 9. The reading output of the memory 9 is subtracted from the digital output of the integrating circuit 7 by the subtracting circuit 10, and the resulting difference in the integrated value of the signal for each vertical scanning period is integrated in the integrating circuit 11.

At this time, if the power supply frequency is 50 Hz when the signal is accumulated for 1/1000 seconds with a scanning cycle of 1/60 seconds, the waveform A in FIG.
As indicated by the shaded area, the integrated value becomes equal every 3V (vertical scanning period), but the integrated value does not become equal every 1V, so the flicker component is accumulated in the integrating circuit 11. Therefore, the output of the integration circuit 11 is compared in the comparison circuit 12 for a predetermined time determined by the reference value generation circuit 13 and the timer circuit 14, and if the integrated flicker component obtained from the integration circuit 11 exceeds the reference value, flicker occurs. The output timing of the timing generation circuit 5 is switched according to the determination signal from the comparison circuit 12, and the accumulation time of the solid-state image sensor 3 is set to 1/100 second via the drive circuit 4.

On the other hand, when the power source frequency is 60 Hz, the output of the integrating circuit 7 is always constant as shown by the chain line portion of the waveform B in FIG. 3 even if the scanning cycle is 1/60 second and the storage is 1/1000 second. The output of the integrating circuit 11 at the subsequent stage does not increase. Therefore, the flicker component is not detected by the comparison circuit 12 within the time set by the timer circuit 14. Therefore, in this case, the solid-state image sensor 3
The accumulation time is set to 1/60 second through the timing generation circuit 5.

Further, the auto iris circuit 8 works to keep the output of the integrating circuit 7 constant at all times, but normally the follow-up time constant is set to be sufficiently long in order to remove the unnatural feeling, so that the detection of the flicker component in the comparison circuit 12 is hindered. There is no such thing. Further, when the power is turned on, the accumulation time of the solid-state image sensor 3 is
It is set to 1/1000 seconds, but it does not take a few seconds to detect flicker, so there is no problem in practical use.

FIG. 4 shows a circuit configuration of another embodiment of the present invention. In this embodiment, the auto iris circuit 8 and the integrating circuit 11 shown in FIG.
A new comparison circuit 17 and a reference value generation circuit 18 are connected between and, and the output of the auto iris circuit 8 is compared with the predetermined reference value of the reference value generation circuit 18 to obtain the output of the auto iris circuit 8. If there is a big change,
That is, this is different from the embodiment of FIG. 2 in that the output of the comparison circuit 17 temporarily prohibits the integration of flicker in the integration circuit 11 when the brightness of the subject changes significantly. This integration prohibition function eliminates the possibility of accumulating a sudden change in brightness of a subject as a flicker that occurs when the imaging device is moved, and thus has an advantage of reducing a flicker detection error.

FIG. 5 shows a circuit configuration of still another embodiment of the present invention in which the frequency of the light source is detected by the white balance sensor. In the figure, 19 is a white balance sensor that detects the color temperature of the illumination light that illuminates the subject for white balance, and uses three sensors that detect red, green, and blue, and red and blue. In some cases, two sensors for detection are used, but either one may be used. A white balance control circuit 20 detects the color temperature from the output of the white balance sensor 19 and controls the R (red) and B (blue) gains in the signal processing circuit 6 according to the detected color temperature. To adjust the white balance.

21 is a sampling circuit, which is once every 1/60 second, for example
The output of the white balance sensor 19 is sampled for a period of 1 ms. 22 is an A / D conversion circuit for A / D converting the output of the sampling circuit 21, and the output of the A / D conversion circuit 22 is supplied to the memory 9 and the subtraction circuit 10 instead of the output of the integration circuit 7. Further, a reset signal is output from the timing generation circuit 5 to the integration circuit 11 and the comparison circuit 12.

Next, the operation of this embodiment shown in FIG. 5 will be described. The sampling circuit 21 samples the output of any one color of the white balance sensor 19 once every 1/60 second for a period of about 1 ms, and after the sampling value is A / D converted by the A / D conversion circuit 22, it is stored in the memory. Store in 9. By subtracting the difference between the sampling value stored in the memory 9 and the sampling value before being stored in the memory 9, the subtraction circuit 10 subtracts the change in the light amount for each vertical scanning period as the flicker amount, and the integration circuit 11
Will be added to. Further, the flicker integration amount obtained from the integration circuit 11 is compared with the comparison circuit in substantially the same manner as the embodiment of FIG.
At 12, the timing signal generation cycle determined by the timing generation circuit 5 is compared with the reference value of the reference value generation circuit 13,
When it is determined that the flicker is detected by the comparison circuit 12, the accumulation time of the solid-state image sensor 3 is set to 1/100 second via the timing generation circuit 5 and the drive circuit 4 by the switching signal of the comparison circuit 12.

At the same time when the comparison circuit 12 finishes the judgment, the reset signal of the timing generation circuit 5 resets the integration result of the integration circuit 11. In this embodiment, the determination as to whether or not there is a flicker is performed not only after the power is turned on, but also periodically, so that even if the fluorescent lamp is always turned on during shooting, for example, The flicker that occurs can be automatically detected and the accumulation time can be freely changed.

〔The invention's effect〕

As described above, according to the present invention, when the flicker of the commercial frequency 50 Hz is detected in the case of the NTSC system, the flicker does not occur by automatically switching the accumulation time of the solid-state image sensor to 1/100 second. In addition, when outdoors or when there is flicker and is in sync (commercial frequency
At 60Hz), the storage time of the solid-state image sensor is automatically switched to 1/60 second, so that high sensitivity is always maintained under usage conditions where flicker does not occur. The remarkable effect that the flicker phenomenon caused by the non-synchronization of the scanning cycle and the lighting frequency of the illumination is eliminated without the troublesome manual switching operation, and that high sensitivity can always be maintained under the use condition where flicker does not occur. Is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing a circuit configuration of an embodiment of the present invention, and FIG. 3 is a timing of a power supply frequency and a storage period at the time of flicker detection. FIG. 4 is a block diagram showing a circuit configuration of another embodiment of the present invention, FIG. 5 is a block diagram showing a circuit configuration of still another embodiment of the present invention, and FIG. FIG. 7 is a circuit diagram showing a schematic circuit configuration of a MOS type solid-state image sensor capable of varying the time, FIG. 7 is a circuit diagram showing a schematic circuit configuration of a CCD type solid-state image sensor capable of varying the accumulation time, and FIG. FIG. 9 is a timing chart showing an example of drive timing for making the accumulation time variable by using the CCD solid-state image sensor, FIG. 9 shows the solid-state image sensor shown in FIG. 7 or FIG.
FIG. 6 is a waveform diagram showing the principle of flicker removal by 1/100 second signal accumulation. 1 ... Lens, 2 ... Aperture, 3 ... Solid-state image sensor, 4 ... Drive circuit, 5 ... Timing generation circuit, 7 ... Integration circuit, 8 ... Auto iris circuit, 9 ... Memory, 10 ... Subtraction circuit, 11 …… Integration circuit, 12,17 …… Comparison circuit, 13,18 …… Reference value generation circuit, 14 …… Timer circuit, 15 …… Power supply circuit, 19 …… White balance sensor, 20 …… White balance control circuit, 21 …… Sampling circuit.

Claims (1)

[Claims] 1. A solid-state image sensor having a variable signal storage time depending on the timing of a drive signal, and a lighting frequency of an illumination means for illuminating a subject imaged by the solid-state image sensor is synchronized with a scanning frequency of the solid-state image sensor. In order to detect whether or not the brightness of the subject is detected, a signal corresponding to the brightness of the subject is detected for each vertical scanning cycle, and a detection output for each vertical scanning cycle is compared with each other. A second comparison calculation means (12) for comparing the output from the comparison calculation means with a predetermined reference value, and an output of the second comparison calculation means has detected that the asynchronous component is at a predetermined level or higher. In this case, the accumulation time of the solid-state image sensor is set to the lighting period of the lighting means so that flicker does not occur, and the accumulation of the solid-state image sensor is detected when it is detected that the asynchronous component is less than a predetermined level. A solid-state imaging device for a television, comprising: switching means for switching so as to increase sensitivity by setting time to the vertical scanning cycle.