Driving device for interline-transfer CCD for use in electronic still camera

An electronic still camera is provided with an interline-transfer CCD having a light-receiving section and a vertical transfer section, and a shutter for intercepting the incoming light. The light-receiving section of the interline-transfer CCD transfers the signal charges at least twice to the vertical transfer section during an open-close operation of the shutter for exposure.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electronic still camera utilizing, as 
the image sensor, an interline transfer CCD, which will hereinafter 
abbreviated as IT-CCD. 
2. Description of the Prior Art 
A fast moving object, recorded with a conventional camera utilizing a 
silver halide film or an electronic still camera utilizing a solid-state 
image sensor appears as a blurred image as shown in FIG. 1A. On the other 
hand, a picture resolved in time, as shown in FIG. 1B, can only be 
obtained by using a flash device providing plural flashes in an exposure, 
in combination with the camera. 
However such flash device used for obtaining pictures resolved in time has 
been associated with various drawbacks such as requiring a high voltage, 
being bulky and inconvenient for transportation. Also such picture can 
only be obtained within the illuminating range of such flash device. 
SUMMARY OF THE INVENTION 
The object of the present invention, therefore, is to provide an electronic 
still camera capable of providing a picture resolved in time, through the 
function of the camera itself, without any additional device such as a 
flash unit. 
The foregoing object can be achieved according to the present invention by 
effecting transfer of signal charges from the light-receiving section of 
an interline-transfer CCD to the vertical transfer section thereof at 
least twice during an exposure of the shutter and accumulating, in said 
vertical transfer section, the signal charges transferred at least twice 
during an exposure of the shutter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 2, there are shown a lens 1; a diaphragm 2; a focal plane shutter 3 
of which exposure time is mechanically determined by the movements of a 
leading curtain and a trailing curtain; and an interline transfer 
charge-coupled device (IT-CCD) 4 constituting a solid-state image sensor. 
In the present embodiment there is employed an IT-CCD with an overflow 
drain. 
A driving device 16 drives the mechanical shutter 3, while another driving 
device 17 drives a liquid crystal shutter 15. A light measuring circuit 19 
measures the luminance of an object, and supplies an output signal to a 
control circuit 20. A setting device 24 selects the number of transfers of 
signal charges from the light-receiving section of the IT-CCD to the 
vertical transfer section during an open period of the shutter 3. An 
operating circuit 18 converts the signal from the IT-CCD 4 into video 
signals and stores the same in a memory 23. A pulse generator 22 generates 
pulses used as reference for driving pulses .phi..sub.v1 and .phi..sub.v2 
for the vertical transfer section of the IT-CCD 4. In response to the 
pulses from pulse generator 22, the control circuit 20 forms the pulses 
.phi..sub.v1, .phi..sub.v2 and supplies the same to the IT-CCD 4. A 
synchronous signal generator 21 supplies vertical synchronization signals 
to the control circuit 20, operation circuit 18 and memory 23. A switch 
SW1 is closed when a release button, for starting the exposure of the 
electronic still camera, is actuated. The pulse generator 22 and the 
synchronous signal generator 21 function in such a manner that the output 
signals thereof have mutually coinciding phases. 
The IT-CCD 4 has a structure as shown in FIG. 3 and comprises 
light-receiving sections 5 for converting the received light into signal 
charges and accumulating said signal charges; transfer gates 7 (TG) for 
controlling the transfer of signal charges from the light-receiving 
sections 5 to vertical transfer sections 6; and a horizontal transfer 
section 8 for transferring the signal charges from said vertical transfer 
sections 6 to a floating diffusion amplifier 9 which converts said signal 
charges to signal voltages of a defined range. 
Adjacent to the light-receiving sections there are provided overflow drains 
10 (OFD) for discharging excessive charges generated in the 
light-receiving sections 5 via, overflow control gates (OFCG) to be 
explained later etc. 
Prior to the explanation of the driving device for an IT-CCD according to 
the present invention, there will be given an explanation of the function 
of the light-receiving section 5, transfer gate 7, vertical transfer 
section 6, overflow drain 10 and overflow control gate in relation to the 
transfer of signal charges, while making reference to FIG. 4A giving a 
cross-sectional view along a line IV--IV in FIG. 3 and to FIGS. 4B-4D 
showing the various potential states. 
As shown in FIG. 4A, which is a cross-sectional view alone a line IV--IV in 
FIG. 3, there are formed, from left to right, an overflow drain 10, an 
overflow control gate 11, a light-receiving section 5, a transfer gate 7, 
a vertical transfer section 6 and a channel stopper 12 as an integrated 
structure on a p-type substrate. 
FIG. 4B shows a state of accumulating a signal charge in the 
light-receiving section 5. In this state the overflow control gate 11 and 
the transfer gate 7 are both in a low (L)-level state, whereby a signal 
charge, represented by a hatched area, is accumulated in the 
light-receiving section 5. An excessive charge, if generated, will not 
flow to the vertical transfer section 6 because of the transfer gate 7 in 
said L-level state, but is drained to the overflow drain 10, flowing over 
the overflow control gate 11 which is likewise in the L-level state. 
Then, FIG. 4C shows a state in which the transfer gate 7 is shifted, from 
the L-level state shown in FIG. 4B, to a high (H) level state. Because of 
said shift, the signal charge accumulated in the light-receiving section 5 
is entirely transferred to the vertical transfer section 6. Subsequently 
the transfer gate 7 is again shifted to the L-level state, and the 
vertical transfer section 6 and the horizontal transfer section 8 shown in 
FIG. 3 are activated. In this manner voltage signals corresponding to the 
signal charges pass through the floating diffusion amplifier 9. 
FIG. 4D shows a state in which the overflow control gate 11 is shifted, 
from the state shown in FIG. 4B, to the H-level state, whereby the signal 
charge accumulated in the light-receiving section 5 is entirely drained to 
the overflow drain 10. In this manner no charge is left in the 
light-receiving section 5. 
In FIG. 5, there are shown a vertical synchronization signal VD; an 
inverted vertical synchronization signal VD; a RELEASE SIGNAL which 
assumes the H-level in response to the closing of the switch SW1; a clock 
signal CLK1; a synchronization signal CLK2 of a shorter period than that 
of said clock signal CLK1; an X-contact signal assuming the H-level in 
response to the full opening of the shutter 3; a trailing curtain signal 
assuming the H-level in response to the movement of the trailing curtain 
of the shutter 3; a TG signal which assumes the H-level for a determined 
period when the vertical synchronization signal is at the L-level, 
independently from the exposure operation, to apply a voltage to the 
transfer gate 7; and pulses .phi..sub.v1, .phi..sub.v2 for driving the 
vertical transfer section 6 after the TG signal assumes the H-level, 
independently from the exposure operation. 
In FIG. 5, a counter 100 measures, during an opening operation of the 
shutter 3, a period corresponding to the interval of plural transfers of 
signal charges from the light-receiving section 5 to the vertical transfer 
section 6, and generates a pulse from a ripple carry port RC upon 
measuring such period of interval. Ports a1, a2, a3 and a4 are provided 
for entering a signal representing said period of interval. A counter 200 
counts, during an opening operation of the shutter 3, the number of 
transfers of signal charges from the light-receiving section 5 to the 
vertical transfer section 6, and generates a pulse from a ripple carry 
port RC when the count reaches a number set by the setting device 24. 
Ports b1, b2, b3 and b4 are provided for entering a signal representing 
the number of times set by said setting device 24. A counter 300 measures, 
during an opening operation of the shutter 3, each accumulating time in 
plural charge accumulations of the light-receiving section 5, and 
generates a pulse from a ripple carry port RC, upon measuring an 
accumulating time represented by a signal entered from input ports c1, c2, 
c3 and c4. There are also provided D-flip-flops D1-D5; AND gates 
AND1-AND9; OR gates OR1-OR3; and NAND gates NAND1, NAND2. The control 
circuit 20 is provided with an operation unit for determining the 
accumulating time and the period of interval in the light-receiving 
section 5 according to the number set by the setting device 24 and the 
output of the light measuring circuit 19, and said operation unit supplies 
a signal representing said accumulating time of the light-receiving 
section 5 to the ports c1-c4, and a signal representing the period of 
interval to the ports al - a4. There are also illustrated signal lines L1, 
L2, L3, L4, L5, L7, L8, L9, L14, L15, L16, L17, L18, L19, L22, L23, L24, 
L25, L26, L27, L29 and L30. 
Now there will be given an explanation of the function of an IT-CCD 
according to the present invention for obtaining a picture resolved in 
time, based on the function of the IT-CCD shown in FIGS. 4B-4D and the 
function of the circuit shown in FIG. 5, and making further reference to 
timing charts of an electronic still camera shown in FIGS. 6 and 7. 
When the power supply to the electronic still camera is turned on, the 
IT-CCD 4 performs an ordinary video operation in response to the vertical 
synchronization signal VD and horizontal synchronization signal .phi.H. No 
signal charge is present either in the light-receiving section 5 or in the 
vertical transfer section 6 in this state, because the shutter is closed. 
Then, when the release signal is shifted to the H-level and the VD signal 
is shifted to the L-level, an H-level signal is entered to the port CK of 
the flip-flop D1 through the line L3 to shift the output Q thereof on the 
line L4 to the H-level. Thus the clock signal CLK1 is supplied to the port 
CK of the counter 100. Also in response to the shift of the line L3 from 
the H-level to the L-level, the driver 16 initiates the movement of the 
leading curtain of the shutter, at a time t.sub.1. The counter 100, 200 or 
300 reads the signal from the ports a1-a4, b1-b4 or c1-c4 when an L-level 
signal is received at the load port and the clock signal is entered to the 
CK port, and initiates the measuring operation when the input to the load 
port is shifted to the H-level. Thus, the counter 100, receiving an 
L-level input to the load port in this state, reads a signal from the 
ports a1-a4. Subsequently, when the shutter 3 becomes fully open, the 
X-contact signal is shifted to the H-level to supply an H-level signal to 
the load port of the counter 100, thus initiating the measuring operation 
thereof. Upon measuring a period corresponding to the time read from the 
ports a1-a4, the counter produces a pulse from the ripple carry port RC, 
whereby the output Q of the flip-flop D2 is shifted to the H-level, and 
the output Q of the flip-flop D3 is thereafter shifted to the H-level in 
response to the start of the clock pulse CLK2. Then, in response to the 
shift of the output Q of the flip-flop D3 to the L-level, the output of 
the AND gate AND3 is shifted to the L-level to supply an L-level signal to 
the overflow control gate 11, thereby prohibiting the flow of charge from 
the light-receiving section 5 to the overflow drain 10 and initiating the 
charge accumulation in said light-receiving section 5, at a time t.sub.3. 
After the shift of the output Q of the flip-flop D3 to the H-level, the 
output Q of the flip-flop D4 is shifted to the L-level in response to the 
start of the clock signal CLK2. The counter 300 reads a signal from the 
ports c1-c4 in response to the shift of the output Q of the flip-flop D2 
to the H-level, and initiates the measuring operation in response to the 
shift of the output Q of the flip-flop D3 to the L-level. Said counter 300 
divides the frequency of the clock signal CLK2 and produces a signal 
obtained by frequency division from ports Q1, Q2, Q3 and Q4. The levels of 
said ports Q1, Q2, Q3 and Q4 at the start of frequency division correspond 
to those of the ports c1-c4 read by the counter 300. When the output 
signals at the ports Q1-Q4 of the counter 300 assume a determined state, 
the gate AND4 outputs an H-level signal, at a time t.sub.4. Said signal 
returns to the L-level after a determined period, at a time t.sub.5. After 
the lapse of a determined period from the returning of said signal to the 
L-level, the counter 300 produces an H-level signal from the ripple carry 
port RC. In response thereto, the output Q of the flip-flop D3 is shifted 
to the L-level, thus clearing the flip-flop D4 and the counter 300, at a 
time t.sub.6. The above-explained procedure in a period from t.sub.3 to 
t.sub.6 is repeated in periods from t.sub.7 to t.sub.10 and from t.sub.11 
to t.sub.14. Then, in response to the shift of the output of the gate AND5 
from the H-level to the L-level, the driver 16 initiates the movement of 
the trailing curtain of the shutter. 
The function of the IT-CCD 4 is effected in relation to the above-explained 
procedure. 
At the time t.sub.3 when the leading curtain of the shutter 3 is fully 
opened, the overflow control gate 11 is shifted to the L-level state. Thus 
the light-receiving section 5 enters the signal charge accumulating state 
as shown in FIG. 4B, wherein signal charges obtained by photoelectric 
conversion of light entering through the shutter in open state are 
accumulated. At the time t.sub.4, the transfer gate 7 is shifted to the 
H-level state while the overflow control gate 11 remains in the L-level 
state, whereby the signal charges accumulated in the light-receiving 
section 5 in a period from t.sub.3 to t.sub.4 are transferred as shown in 
FIG. 4C to the vertical transfer section 6, which therefore stores the 
image in a period from t.sub.3 to t.sub.5, including the charge when the 
transfer gate is activated. 
At the time t.sub.5, the transfer gate 7 is again shifted to the L-level 
state, thereby restoring the state of FIG. 4B in which the light-receiving 
section 5 is separated from the vertical transfer section 6. Then, at the 
time t.sub.6, the overflow control gate 11 again assumes the H-level 
state, whereby the charge generated in the light-receiving section 5 is 
forcedly discharged to the overflow drain 10 as shown in FIG. 4D. Said 
forced drainage of charge continues to the time t.sub.7, after which the 
procedure the same as in the period of t.sub.3 to t.sub.6 is repeated, and 
a new instantaneous image is transferred to the vertical transfer section 
6 in a period of t.sub.7 to t.sub.10. Consequently said vertical transfer 
section 6 stores added charges obtained by two or more transfers of signal 
charges. 
The trailing curtain of the shutter starts to run at t.sub.13, after 
repeating the above-mentioned procedure at least twice. 
The period of exposure obtained in such procedure is intermittent in time 
as shown in FIG. 6, so that there is obtained an image, which, as shown in 
FIG. 1B, is resolved in time. Since the vertical transfer section 6 is not 
driven in a period of t.sub.1 to t.sub.13 in which the shutter is opened, 
there appears no vertically flowing smear in the image as in the 
conventional video camera utilizing an IT-CCD. However, a charge generated 
in a deep part of the substrate of the light-receiving section may enter 
the vertical transfer section while it is not driven. In order to avoid 
such phenomenon, a liquid crystal shutter 15 is placed between the 
mechanical shutter and the solid-state IT-CCD and is activated in the 
exposure periods t.sub.3 -t.sub.5, t.sub.7 -t.sub.9 and t.sub.11 
-t.sub.13. It is to be noted, however, that the object of the present 
invention can be achieved without such liquid crystal shutter, though the 
circuit shown in FIG. 2 includes such liquid crystal shutter. 
In the IT-CCD driving method of the present invention, the charges 
accumulated in the vertical transfer section may exceed the ability of 
charge $ transfer thereof, since the signal charges generated in the 
light-receiving section are added at least twice in the vertical transfer 
section. In such case, the signal charges in the light-receiving section 
are drained into the overflow drain after the trailing curtain of the 
shutter is closed, and the light-receiving section is placed in the charge 
accumulating state and the signal charges, accumulated in the vertical 
transfer section and exceeding the transfer ability thereof, are returned 
to the light-receiving section. In such charge returning operation, the 
excessive signal charges are drained to the overflow drain 10 through the 
overflow control gate 11 as shown in FIG. 4C, and the signal charges are 
then again transferred to the vertical transfer section for signal 
readout. In this manner the signal transfer can be achieved without 
problem even if the signal charges accumulated in the vertical transfer 
section exceed the transfer ability thereof. 
The number of resolution or division in time can be arbitrarily modified by 
the timing of the driving pulses for the overflow control gate and the 
transfer gate in the IT-CCD, and the interval in time is exact. For this 
reason the device of the present invention can also be used as a measuring 
apparatus for precisely measuring the movement of an object from the 
movement of an image divided in time. 
According to the present invention, it is also to be noted that the entire 
image frame, or all the pixels, of the IT-CCD are simultaneously exposed 
at each of plural charge transfer. Making use of this feature, the device 
of the present invention can also be utilized as a camera for observing 
meteors, with a continuously open shutter, by cooling the IT-CCD to 
prolong the charge retaining period of the vertical transfer section.