JP2688083B2 - Electronic still camera - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electronic still camera that captures a still image using a solid-state image sensor.

2. Description of the Related Art Conventionally, an electronic still camera reads unnecessary charges accumulated in a solid-state image sensor before actual exposure, performs photoelectric conversion and charge accumulation by actual exposure, and captures and records a still image. It is connected.

The configuration of the electronic still camera will be described below with reference to the drawings. FIG. 2 is a block diagram showing the structure of an electronic still camera, and FIG. 3 is a schematic diagram of a CCD solid-state image pickup device.

In FIG. 2, reference numeral 1 is a lens, and a mechanical shutter 2 thereof is driven by a shutter drive circuit 5. 3 is CC
The solid-state image pickup device D is driven by the image pickup device drive circuit 6, and its output is sent to the video signal processing circuit 4. The system controller circuit 7 controls the timing of driving the mechanical shutter 2, the timing of driving the CCD solid-state imaging device 3 to store and transfer charges, and the operation timing of the video signal processing circuit 4.

In FIG. 3, the CCD solid-state image sensor 3 includes a first field light receiving portion 11 arranged in a matrix corresponding to each picture element of the first field, and a matrix corresponding to each picture element of the second field. The second field detectors 12 are arranged in a matrix, and the first and second field detectors 11 and 12 are connected to a vertical transfer register 14 through a transfer gate 13 provided for each picture element. These vertical transfer registers 14 are connected to a horizontal transfer register 15 provided at one end thereof.

Next, the conventional operation will be described with reference to the timing chart of FIG. Electric charges are accumulated in each pixel of the first field light receiving portion 11 and the second field light receiving portion 12 of the CCD solid-state image pickup device 3 by exposure. Now, when the recording mode is the frame mode, first, in synchronization with the transfer gate pulse (FIG. 4 (b)) synchronized with the vertical synchronization signal (FIG. 4 (a)),
The transfer gate 23 provided in each pixel of the first field light receiving portion 21 is opened, and the accumulated signal charges are transferred to the vertical transfer register.
Moved to 14. During this time, the charge accumulated in each picture element of the second field light receiving portion 12 is not transferred because the transfer gate 23 remains closed. The signal charges transferred to the vertical transfer register 14 are vertically transferred to the horizontal transfer register 15 in synchronization with a horizontal synchronizing signal (not shown) by one horizontal line at a time for each horizontal scanning period 1H, and the horizontal transfer register 15 is transferred. It is sequentially read out via. In synchronization with the next transfer gate pulse, the transfer gate 13 of each picture element of the second field light receiving unit 12 is opened, the signal charges accumulated in each picture element are transferred to the vertical transfer register 14, and then the above-mentioned It is read in the same process as in the case of the first field.

When the recording mode is the field mode, the signal charge accumulated in each picture element of the first field light receiving unit 11 and the second field light receiving unit 12 is synchronized with the transfer gate pulse to generate the first and second signals.
All the transfer gates 13 provided in both picture elements of the field light receiving portions 11 and 12 are opened and transferred to the vertical transfer register 14. The signal charges transferred to the vertical transfer register 14 are vertically transferred to the horizontal transfer register 15 by two horizontal lines every 1H for one horizontal scanning period in synchronization with a horizontal synchronizing signal (not shown). It is sequentially read out via.

When a release switch (not shown) is pressed at the time of photographing, first, with the mechanical shutter 2 opened, photometry for determining the shutter speed and the like is performed using the signal of the solid-state image sensor 3. Then, after the photometry is completed, the mechanical shutter 2 is closed (FIG. 4 (c)), and at the same time, the frame,
The field read mode is set (FIG. 4 (d)). At the time of photometry, the unnecessary residual charge accumulated in the state where the mechanical shutter 2 is opened is read out in the recording mode set during the closing (this is called charge sweeping out). After sweeping out the electric charge for a fixed time t, the mechanical shutter 2 is opened for an arbitrarily set shutter time t ′ in synchronization with the vertical synchronizing signal, and the CCD solid-state image sensor 3 is exposed. After the exposure is completed, the signal charges accumulated in the CCD solid-state image sensor 3 are read out by the recording gate signal (FIG. 4 (e)) in the mode set according to the transfer process in synchronization with the transfer gate pulse. , And transferred to and recorded in the video signal processing circuit 4. This recording period is two vertical synchronization periods in the case of frame recording and one vertical synchronization period in the case of field recording.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described configuration, in a solid-state imaging device with many afterimages, it is necessary to lengthen the time for discharging charges in order to sufficiently reduce the residual charges that cause the afterimages. , The time lag between pressing the shutter and the actual exposure cannot be ignored. On the contrary, set the recording time (2 vertical synchronization periods for frame recording, 1 vertical synchronization period for field recording) in the mode in which the time for sweeping out the charge is shortened and the time from pressing the shutter to the start of exposure is set. In that case, since the read-out can be performed only once during the charge sweep-out period, the accumulated charge cannot be read sufficiently, the residual charge increases, and a problem such as flickering occurs.

Here, the accumulated charge at the time of actual exposure is necessary, and it is transferred in synchronization with the vertical sync signal and the horizontal sync signal,
Although it must be read out, the charge accumulated during photometry is unnecessary and does not need to be accurately transferred in time. Further, the accumulated charges are inevitably transferred by the transfer gate pulse, and the residual charges are certainly decreased and never increased by the transfer.

The present invention solves the above problem, and takes into consideration that unnecessary charges accumulated during photometry do not have to be transferred accurately in time, and a plurality of read operations are performed during the same charge sweep period as in the related art. It is an object of the present invention to provide an electronic still camera that can reduce the residual charge by performing the above.

Means for Solving the Problems To solve the above problems, an electronic still camera according to the present invention includes a solid-state imaging device having a photoelectric conversion unit, a charge storage unit, a vertical transfer unit and a horizontal transfer unit, and the solid-state imaging device. The solid-state image pickup device includes a driving unit and a shutter for exposing the solid-state image pickup device for a predetermined time, and the solid-state image pickup device driving unit sets the first vertical synchronization signal period before the shutter is opened for exposure. Charges accumulated in the photoelectric conversion means of the solid-state image sensor are transferred to the vertical transfer section and swept out a plurality of times, and the charges of the vertical transfer section and the horizontal transfer section are transferred during the next one vertical synchronizing signal period. Is.

Operation With the above-described configuration, at the time of sweeping out the charges after the shutter that has been opened for photometry is closed, one or more transfer gate pulses are output from the image pickup device drive circuit to the solid-state image pickup device, and Therefore, since the transfer gate is opened, the charges accumulated in the photoelectric conversion means are transferred to the vertical transfer unit more times than in the conventional case. As a result, the unnecessary charges accumulated by photometry and the like can be sufficiently swept out within the same sweeping time as in the conventional case, and the residual charges can be sufficiently swept out even in the solid-state imaging device with many afterimages, and flickers do not occur. .

Embodiment An electronic still camera according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a timing chart in the electronic still camera of one embodiment of the present invention, and the operation will be described with reference to FIGS. 2 and 3. When a release switch (not shown) is pressed, the shutter drive circuit 5 opens the mechanical shutter 2 and the solid-state image sensor 3 is used to determine the exposure time and other processes such as photometry. Circuit 4
When the photometry is completed, the system control circuit 7 closes the mechanical shutter 2 via the shutter drive circuit 5. After the mechanical shutter 2 is closed, the image pickup device driving circuit 6 adds a transfer gate pulse synchronized with a normal vertical synchronizing signal (Fig. 1 (a)), as shown in Fig. 1 (b).
Transfer gate pulses are sent to the solid-state imaging device 3 a plurality of times within one vertical synchronization signal period (FIG. 1 (b)), and unnecessary residual charges accumulated while the mechanical shutter 2 is opened are removed by the mechanical shutter. Sufficient sweeping is performed while the expression shutter 2 is closed (Fig. 1 (c)).

Then, the normal transfer mode is set in synchronization with the next vertical sync signal, and the frame / field read mode is set by the system control circuit 7 (first
Figure (d). As a result, the residual charges swept a plurality of times in the vertical transfer unit during the previous one vertical synchronizing signal period are also transferred from the vertical transfer unit. After the time T required for the signal to stabilize after the mode switching, the mechanical shutter 2 is opened and exposed for a time T'in synchronization with the next vertical synchronizing signal (first time).
Figure (c). Subsequent operations are the same as in the conventional example.

As described above, according to the present embodiment, the image pickup device driving circuit 6 outputs a larger number of transfer gate pulses to the CCD solid-state image pickup device 3 during the charge sweep period having the same length as the conventional one, and therefore, during photometry. The charge accumulated in each picture element of the light receiving portion is transferred more and the residual charge is sufficiently swept out, so that the problem such as flickering can be prevented.

EFFECTS OF THE INVENTION As described above, according to the present invention, from the photometry to the exposure, during the charge sweeping period while the shutter is closed,
The accumulated charge remaining in the photoelectric conversion unit is transferred to the vertical transfer unit more times than before, and then the sweeping is stopped and the read mode of the solid-state image sensor is set, so that it remains even in the solid-state image sensor with many afterimages. It is possible to sufficiently sweep out the charges, eliminating the adverse effects such as flicker,
The excellent effect that the frame / field can be stored can be obtained.

[Brief description of the drawings]

FIG. 1 is a timing chart of an electronic still camera according to an embodiment of the present invention, FIG. 2 is a block diagram of the electronic still camera, FIG. 3 is a schematic diagram of a solid-state image pickup device, and FIG. 4 is a conventional electronic still camera. It is a timing diagram of a camera. 2 ... Mechanical shutter, 3 ... CCD solid-state image sensor, 6
...... Imaging element drive circuit, 11 ...... First field light receiving part,
12 …… Second field light receiving part, 13 …… Transfer gate.

Claims (1)

(57) [Claims] 1. A solid-state image pickup device having a photoelectric conversion means, a charge storage means, a vertical transfer part and a horizontal transfer part, a means for driving the solid-state image pickup device, and for exposing the solid-state image pickup device for a predetermined time. The solid-state image pickup device driving means, before the shutter is opened for exposure, charges the electric charge accumulated in the photoelectric conversion means of the solid-state image pickup device a plurality of times during the first vertical synchronization signal period. An electronic still camera, characterized in that the charges are transferred to the vertical transfer unit and are swept out, and the charges of the vertical transfer unit and the horizontal transfer unit are transferred during the next one vertical synchronizing signal period.