JP2754604B2 - Driving method of electronic shutter - Google Patents

Description

The present invention relates to a method for driving an electronic shutter used in a still video camera or the like.

[Prior art] A so-called electronic shutter using a CCD, which is a solid-state imaging device, is generally used as a shutter for a still video camera or the like. Is read out in synchronization with the vertical synchronizing signal of the video processing circuit (for example, see “Television Technology”, August 1987, pp. 37-39).

However, when the signal charges are read out to the vertical transfer unit in this manner, the timing corresponding to the opening of the shutter is fixed because the timing corresponding to the opening of the shutter is fixed. Is restricted by the vertical synchronizing signal. For this reason, the time from the arbitrary timing of the release to the timing of the shutter opening varies, and furthermore, the shutter opening time is calculated by the pre-metering data. Exposure metering, and exposure control tends to vary, especially when flash emission is required.
There is a limit to the improvement of photometric accuracy.

A method of driving an electronic shutter in synchronization with a release switch is also known.
No. 173), no consideration is given to making it possible to always output the shutter opening timing.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned conventional problems. The electronic shutter can be arbitrarily opened and closed regardless of the timing of a video vertical synchronizing signal. An object of the present invention is to provide a driving method of an electronic shutter that enables time photometry and improves photometric accuracy, that is, exposure accuracy.

Means for Solving the Problems The present invention relates to a method of driving an electronic shutter using an imaging element having a photoelectric conversion unit and a transfer unit and having a function of sweeping out unnecessary charges in the transfer unit. Unnecessary charge from the transfer unit is continuously discharged during the exposure of the transfer unit, and the transfer unit is not required at the point before the end of the exposure for the time necessary to allow the transfer unit to accept the potential signal charge from the end of the unnecessary charge sweeping. Discharging the charge is stopped, and when the exposure amount of the imaging element reaches a desired appropriate amount, the accumulated charge of the photoelectric conversion unit is read out to the transfer unit, and the read charge is transferred and output by the transfer unit. This is a method for driving an electronic shutter.

[Operation] According to this driving method, unnecessary charge sweeping of the image sensor is stopped at a predetermined level that is equal to or lower than the appropriate exposure level, and after waiting for a certain time until the potential of the transfer unit can accept charges, vertical synchronization is performed. Regardless of the synchronization with the signal,
The signal charges that have reached the proper exposure are read out to the transfer unit.

[Embodiment] FIG. 1 shows an embodiment of an electronic shutter control device in a still video camera in which the driving method of the present invention is implemented.

In the figure, the core of the electronic shutter is a CCD 1 serving as an image pickup device for performing photoelectric conversion, a V timing circuit 2 and a V driver 3 for generating drive pulses for vertical transfer and horizontal transfer for driving and controlling the CCD 1. And an H timing circuit 4.

As shown in FIG. 2, the CCD 1 includes a photoelectric conversion (imaging) unit 11 including a large number of photodiodes, a memory unit 12,
It has a horizontal read CCD 13 and a draining drain 14,
Vertical transfer CCD 15 of photoelectric conversion unit 11 and V transfer CCD of memory unit 12
Drive control is performed by applying a drive pulse to 16 or the like.

The V timing circuit 2 is a four-phase pulse φVN (hereinafter, referred to as a “pulse”) for driving the vertical transfer CCDs 15 and 16 (high-speed reverse transfer of unnecessary charges to a drain and high-speed transfer of signal charges to a memory unit). Simply referred to as φVN) and a pulse FSPN for transferring the charge of the photoelectric conversion unit 11 to the vertical transfer CCD 15
(Hereinafter simply referred to as FSPN), a signal for starting accumulation of signal charges to the CCD1, that is, a signal EXP1 (hereinafter simply referred to as EXP1) for giving a shutter opening timing, and a circuit for generating a vertical synchronization pulse V _SYNC for φVN. Having a part.

The V driver 3 supplies φV + FSP to the CCD1 based on φVN and FSPN, and the H timing circuit 4 outputs the horizontal read CCD1
The signal φH for driving 3 is output. EXP1 is release switch S
The signal becomes "H" by an ON signal from W, and becomes "L" in synchronization with a predetermined FSPN.

The photometry unit 5 has a function of performing pre-photometry before exposure of the CCD 1 and a function of performing real-time photometry when the shutter is opened.
As described later, a signal EXP2 (hereinafter referred to as a signal) that switches from the pre-metering to the real-time metering at the timing of “H” → “L” of EXP1, and then stops the high-speed reverse transfer of the unnecessary charges to the drain. , Simply EXP2).

As shown in the figure, the photometric unit 5 includes a pre-photometric element D1, an operational amplifier 51, a resistor R, a correction voltage unit 52, a switch S1, and a capacitor C1, a real-time photometric element D2, and an operational amplifier. It comprises a real-time photometric unit comprising 53, a capacitor C2 and a switch S2, an operational amplifier 54, and a comparator 55.

The flash control unit 6 that drives the flash operates upon receiving a signal passed through the timer 7 of EXP1 and EXP2.

The video processing circuit 8 receives the signal charge read from the horizontal read CCD 13 of the CCD 1 and converts the signal charge into a signal for recording an image on a recording unit 9 such as a magnetic disk.

The power supply section 10 receives the ON signal of the release switch SW and supplies power to each section of the circuit.

Next, the operation of the electronic shutter having the above configuration will be described with reference to the time chart of FIG.

(1) Unnecessary charge sweeping period When the release switch SW is turned on, power is supplied to each part of the circuit, and FSPN and φVN are given to the driver 3 to drive the CCD1.

That is, the unnecessary charges accumulated in the CCD1 are transferred to the vertical transmission CCD by the FSPN, and the unnecessary charges are swept out by the φVN to be rapidly reversed to the drain. The sweeping by φVN is repeated several times (n times) so that there is no remaining sweeping. At this time, EXP1 is "H" and the switches S1 and S2 are in the ON state.

(2) Signal charge accumulation period In synchronization with the n-th FSPN, EXP1 is changed from “H” to “L”, unnecessary charges are transferred to the vertical transfer CCD at φVN, and accumulation of signal charges is started (shutter open). Unnecessary charges transferred to the vertical transfer CCD are reversely transferred at a high speed and swept out to the drain.

At this time, in order to sweep out smear components (unnecessary charges) generated in the vertical transfer CCD as much as possible, the high-speed transfer is continued.

By the way, after that, the accumulated signal charges are transferred vertically.
In order to read data to D, the potential of the vertical transfer CCD must be set so as to receive charges.

Now, CCDs for vertical transfer of signal charges from the stop of high-speed reverse transfer
T (constant)
And

By the way, even if it is instructed to read out the signal charge to the vertical CCD when the exposure becomes proper by the real-time photometry of the shutter opening, the charge accumulation continues for the time T, and the exposure is properly adjusted by this amount. Exceeds the value.
However, if the light amount of the real-time photometry is known, the exposure amount during T is known.

Therefore, if a reverse transfer stop command is issued at a low level by the exposure amount during T, the signal charge is read out to the vertical transfer CCD after T time, so that the signal to be read can be properly exposed. .

At the timing of “H” → “L” of EXP1 described above, the switches S1 and S2 are turned off, but before that, the light amount is pre-metered by the pre-metering element D1, and the correction voltage unit 52 Then, a voltage lower than the appropriate level is generated by the exposure amount of the time T and is held in the capacitor C1, and the value immediately before the start of signal charge accumulation at the timing of “H” → “L” of EXP1 is held.

On the other hand, when the switch S2 is opened at the same time as the start of signal charge accumulation, real-time photometry by the real-time photometric element D2 and the capacitor C2 starts. And this photometric value is
When the level reaches the level lower by the exposure amount during the time T, the output of the comparator 54, that is, EXP2 changes from “H” to “L”.

The high-speed reverse transfer is stopped by the signal of “H” → “L” of EXP2, FSPN is generated after time T, and the signal charge is transferred to the vertical transfer CCD (shutter closed).

(3) Standby period V transfer CCD after high-speed transfer to memory
The signal charges transferred to the memory section are transferred at high speed by φVN. Therefore, the control waits until the vertical synchronization signal _VSYNC is input.

(4) Signal processing and recording period After V _SYNC is input, the signal charges are read out from the horizontal read CCD of CCD 1 to the video processing circuit 8 by the TV synchronization, and the signal processing is performed. To record.

 Next, the shortest shutter speed will be described.

EXP1 changes from “H” to “L” and unnecessary charges are transferred vertically
The signal charge is transferred to the CCD, but the signal charge cannot be transferred to the vertical transfer CCD until all the unnecessary charges are swept out. Therefore, the time required to sweep out only once is
If Tr, Tr + T is the shortest shutter speed.
If EXP2 changes from "H" to "L" during this Tr, the shortest shutter speed is automatically set.

Next, the use of the flash will be described. The flash emits light with a delay of Tr time from the timing of “H” → “L” of EXP1. This is between Tr
This is to prevent EXP2 from changing from “H” to “L”. In addition, the flash emission stops when EXP2 changes from “H” to
It is assumed that the timing becomes “L”.

 FIG. 4 shows the configuration of the second embodiment.

In the present embodiment, the configuration of the photometry unit 5 and the timing operation of photometry are different from those described above.

The photometric unit 5 includes a photometric element D0, an operational amplifier 56, a voltage source E corresponding to an appropriate exposure level, a switch S0 that opens and closes with the signal EXP0 to connect and disconnect the voltage source E, and a capacitor C0 charged by the voltage source E. And the charge of the capacitor C0
And a capacitor that discharges according to the output of
It comprises a comparator 55 which is activated by the voltage of C0 and outputs EXP2.

In the above-described embodiment, the high-speed reverse transfer is stopped at the time of the exposure level lower by the exposure amount corresponding to the time T than the appropriate exposure, but in this embodiment, the photometry is performed more than the start of the charge accumulation in the CCD. It is started earlier by T, and the high-speed reverse transfer is stopped when the proper exposure is obtained by photometry. Even in this case, the charge accumulation in the CCD is started after T after the start of photometry.
However, since the actual accumulation of signal charges ends T time after "H" → "L" of EXP2, the exposure is proper at the end of accumulation.

The operation of the photometer, mainly of the electronic shutter according to the second embodiment, will be described with reference to the time chart of FIG.

(1) Unnecessary charge sweeping period When the release switch SW is turned on, EXP0 becomes “L”.
→ "H", and the switch S0 turns ON. Therefore, the capacitor C0 is charged by the voltage source E corresponding to the appropriate exposure level. T time before the start of signal charge accumulation at EXP1 “H” → “L” timing by nth FSPN
EXP0 is changed from “H” to “L”, whereby the switch S0 is turned off, and photometry is started.

During photometry, the electric charge of the capacitor C0 is discharged through the transistor Q according to the amount of light that strikes the element D0.

(2) Signal charge accumulation period EXP1 changes from “H” to “L” T times after the n-th FSPN, that is, the timing of “H” → “L” of EXP0, and accumulation of signal charges starts at CCD1 (shutter). Open).

When the capacitor C0 is completely discharged, EXP2 changes from “H” to “L”, and the high-speed reverse transfer is stopped to discharge unnecessary charges of the CCD1 by φVN.

Thereafter, the CCD 1 further accumulates the signal charge for the time T, and transfers the charge to the vertical transfer CCD by FSPN (shutter closed).

 Subsequent operations are the same as described above, and a description thereof will be omitted.

The relationship between the exposure amount of the photometric element D0 and the exposure amount of the CCD1 in the above operation will be described. From EXPO “H” → “L” to EXP1 “H” → “L” (shutter open). Time T
Indicates that only the photometric element D0 is exposed, and only the CCD1 is exposed during a time T from when the EXP2 changes from "H" to "L" to FSPN (shutter close).

Therefore, the exposure amounts at these two times must be equal. For this reason, the flash is “H” of EXP1 →
It is assumed that light is emitted between “L” and “H” → “L” of EXP2.

In each of the above embodiments, the accumulation time is controlled by the amount of light received by another photometric element during the charge accumulation of the CCD 1, but before the accumulation is started, an appropriate time according to the received light output is obtained by calculation. You may make it control.

That is, in this case, the time 2 ^-Tv as the appropriate exposure based on the light output of the light measuring section (although, Tv is apex value of the exposure time or storage time) to calculate the time from the storage time of 2 ^-Tv has elapsed At this point, an accumulation stop signal is output.

In this case, when performing flash photography, 2
^At the time of ^-Tv , the flash is ^{started to fire} at a timing that goes back so that the flash completely stops emitting light, and the reflected light from the subject due to the flash emission is received by a light receiving element different from the CCD, and The light emission stop signal may be output when the amount of received light reaches the predetermined level.

FIG. 6 shows the configuration of the photometric unit according to the third embodiment.

This photometric unit includes a spot photometric unit 61 that measures the subject brightness at the center of the shooting screen, a peripheral photometric unit 62 that measures the subject brightness at the peripheral portion, and a computing unit 63 to which each photometric brightness value Bvs, Bva is given. , A timer I receiving the calculation output of the calculation unit 63 and outputting EXP2, and a timer receiving the calculation output and EXP1
II, and a flash light control circuit 64 for controlling flash light emission.

The photometric circuit section 64 includes a light receiving element 65, a capacitor 66, a switch 67, an operational amplifier 68, and a comparing section 69. The AND output of the flash enable (EN) signal from the arithmetic unit 63 and the output of the timer II is used as a light emission start signal. With this output, the switch 67 is opened and the charging of the capacitor 66 is started. Further, the output of the operational amplifier 68 and the D / A conversion output from the operation unit 63 are compared by the comparison unit 69,
A light emission stop signal is output.

The procedure of the calculation by the calculation unit 63 is shown in the flowchart of FIG. To explain this procedure, first, the central luminance value
The image sensor α [apex value] of Bvs and the peripheral luminance value Bva is obtained (# 1). If α is smaller than 2, it is determined that the light is normal and the processing of # 3 and below is performed. If α is not smaller than 2, , And performs the processing of # 14 and below.

During direct light, calculate the average value from Bvs and Bva, and calculate it as Bvs
(# 3), and Bvc + Svc−Avc is set as the exposure time Tv [apex value]. Here, Svs is the sensitivity of the CCD, and Avc is the aperture value of the photographing optical system [all are apex values]. next,
Tv is compared with the camera shake limit time Tvh. If the former is smaller than the latter, the low-luminance forward light processing of # 6 to # 10 is performed, and if the former is smaller, the high-luminance forward light processing of # 11 to # 13 is performed. .

At the time of low-luminance forward light, the above Tvh is used as a control value Tvc of the exposure time (# 6), and the flash is fired (# 6).
7) to obtain proper exposure. Then, 2- ^Tvc- T is set in the timer I for determining the shutter closing EXP2 (# 8), and the timer II for determining the flash ^firing timing is set.
Is set to 2- ^Tvc- T-Tf (where Tf is the total light emission time of the flash) (# 9). Further, the D / A conversion output (# 10) of Svc is given to one input terminal of the comparator 69, and the light receiving element 65
The light emission is stopped when the light emission amount of the light reaches a certain level.

At the time of high-brightness ^direct light, time control is performed using the Tv value based on the average photometric value obtained in # 4 (# 11), the flash is not emitted (# 12), and the timer I is set to 2 ^-Tvc -T. Yes (# 1
3).

Next, at the time of backlight, Bva + Svc-Avc-1 is set to Tv so as to control the time when the surroundings exceed 1 Ev (# 1
Four). Next, a limit of the camera shake limit time Tvh is given to Tv (#
15 to # 17), and set to flash light emission (# 18). further,
Timers I and II are set in the same manner as in # 8 and # 9 described above (# 19,
# 20), Tvc + Avc−Svc−Bvs is used as a correction value β (# 21),
The Svc + β D / A conversion output (# 22) is compared with the comparator 69 in the same manner as described above.
Give to. This allows the flash to have a central brightness Bv
In consideration of s, the central portion emits light in an appropriate amount.

[Effects of the Invention] As described above, according to the electronic shutter driving method of the present invention, the high-speed reverse transfer is stopped at a level lower than the appropriate exposure by a predetermined amount, and the potential of the vertical transfer unit until the potential of the vertical transfer unit accepts the signal charge. The signal charge is read out to the vertical transfer unit after waiting for a certain period of time, so that the signal charge stored in the image sensor to an appropriate level is read out to the vertical transfer unit at any time without synchronization with the vertical synchronization signal. This makes it possible to perform real-time photometry and obtain a shutter with high exposure accuracy.

In addition, since unnecessary charges in the vertical transfer unit are also discharged during the signal charge accumulation period (exposure period), low smear can be achieved.

Furthermore, when a flash is used, unnecessary charges are always swept out at the time of flash emission where smear is likely to occur, so that smear can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic shutter of a video camera according to a first embodiment for executing a method of driving an electronic shutter according to the present invention, FIG. 2 is a block diagram showing an example of an image sensor serving as a core of the shutter, FIG. 3 is a time chart showing the operation of the first embodiment, FIG. 4 is a configuration diagram showing the second embodiment, FIG. 5 is a time chart showing the operation of the second embodiment, and FIG. FIG. 7 is a configuration diagram of a photometric unit in the example, and FIG. 7 is a flowchart showing a calculation procedure in the third embodiment. 1 ... CCD (image sensor), 2 ... Vertical timing circuit,
5: Photometry unit, 6: Flash control unit, 15, 16: Vertical transfer CCD.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Nobuyuki Taniguchi 2-30 Azuchicho, Higashi-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Camera Co., Ltd. (56) References JP-A-63-248288 (JP, A) JP-A-63-169180 (JP, A) JP-A-1-170281 (JP, A) JP-A-59-40779 (JP, A)

Claims (1)

(57) [Claims] An electronic shutter driving method using an image pickup device having a photoelectric conversion unit and a transfer unit and having a function of sweeping out unnecessary charges in the transfer unit, wherein the transfer unit is not required during exposure of the photoelectric conversion unit. The sweeping of the charge is continued, and the sweeping of the unnecessary charge from the transfer unit is stopped at a time before the end of the exposure for a time necessary for the potential of the transfer unit to be in a state of accepting the signal charge from the end of the sweeping of the unnecessary charge, A method for driving an electronic shutter, comprising: when the exposure amount of an imaging element reaches a desired appropriate amount, reads out the accumulated charge of the photoelectric conversion unit to a transfer unit, and transfers and outputs the read charge by the transfer unit.