JPS63193776A - Image pickup device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of blooming even if field reading is executed through the use of a transfer CCD which is designed for frame reading and which has a small saturation potential by providing a means which interlocks to a switching action for field reading and frame reading and switch overflow levels in respective picture elements. CONSTITUTION:The optimum values Va and Vb of an overflow drain voltage VOFD in field reading and frame reading are written in an EEPROM30, and when a switch 6 changes over to field reading or frame reading, the values of the optimum overflow drain voltage VOFD in a reading mode are read from the EEPROM, converted into voltage by a D/A converter 31, and are supplied to a bias circuit 5, whereby they are impressed on a CCD1. With interlocking to the switching action for field reading and frame reading, and switching the overflow levels in respective picture elements, an image pickup element can be driven at an optimum condition without damaging a blooming-proof characteristic at the time of field reading.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an imaging device that can perform both field readout and frame readout modes when reading signals from an image sensor.

[Prior Art] FIG. 4 is a block diagram schematically showing the main parts of a conventional m-image device that cannot be switched between field readout and frame readout.
1 is a CCD, 2 is a signal processing circuit, 3 is a drive circuit that drives the CCDI, 4 is a clock generation circuit that generates drive pulses for the CCD 1 and pulses used in the signal processing circuit 2, and 5 is a circuit that generates the bias required by the CCD 1. 6 is a switch for switching between field readout and frame readout, 20 is a system control unit that controls the entire system, 21 is a lens and aperture, 22
is the shutter.

FIG. 5 is a diagram schematically showing a CCD used in the first [-1], and is a photodiode section as one pixel.

For example, it is an interline CCD with a vertical overflow drain structure. 8 is a photodiode, 9 is a superimposed CCD register (hereinafter referred to as V-CCD), and 10 is a wood p
ccD register (hereinafter referred to as H-CCD), ii is charge detection pin, 12 is transistor switch, φvl, φv2
．． φv3. φv4 is a terminal. Further, 40 is the overflow train voltage V. It is ro.

When a high-brightness object enters the screen and the potential of the photodiode in the high-brightness pixel area rises extremely, the excess charge generated in the photodiode 8 of the CCD shown in FIG. is output in the direction of the substrate beyond the potential barrier. This suppresses fluming.

FIG. 6 is a drive timing chart during field readout, and FIG. 7 is a drive timing chart during frame readout.

In the block diagram of FIG. 4, when the switch 6 is set to the field side, the charge readout from the CCD 1 is 0'.
It is carried out at the timing shown in Figure 56. In FIG. 5, terminals φvl and φv3 are transfer electrodes for transferring charges within the V-CCD in CCD 1, and charge shift electrodes for transferring charges from photodiode 8 arranged corresponding to each pixel to V-CCD 9. It also serves as a gate. Terminal φvl
.

φv3 takes three values as shown in FIGS. 6 and 7, and when clocked between the low (L) level and the middle (M) level, V-CCD transfer is performed and the high (H) level, photodiode 8 to V-CCD9
The charge is shifted to H− at the next timing.
Transfer to COD and form No. 1 on the image. Next, field readout and frame readout will be explained using FIGS. 6 and 7.

61st: In 'A, in the odd field, the terminals φvl and φv3 become H level at the same time in the part (A), so that the charges in the A row and B row of the photodiode 8 are simultaneously transferred to V-C.
After shifting to CD9 and adding the charges of row A and row B in part (B), the inside of V-CCDQ is transferred. Similarly, line A′,
The charges in row B' are added and transferred. Next, in the even field, in part (C), are the charges in rows A and B simultaneously read out? In part (D), is the electrode φv1 at the M level?
The A row is not transferred, and 710 is calculated between the B row and A' row, that is, the total number field, which is shifted by one row. This reading method is called field reading because the signal from each photodiode 8 is usually read out once per field.

Next, in the case of frame readout, in FIG. 7, in the odd field, the terminal φv1 becomes H level at part (E), and charges in rows A and A' are read out. In the even field, the terminal φV3 in the (F) section becomes H level, and the charges in the B and B' rows are read out. In this readout method, the signal of each photodiode 8 is usually read out once every frame, so it is called frame readout.

FIG. 8 is a schematic diagram of an imaging sequence in an electronic still camera. To explain field readout and frame readout in an electronic still camera, Fig. 8(a)
When reading the field, CC
The dark current in DI is cleared and the shutter 22 is opened and exposure is performed. Next, after closing the shutter 22 and completing the exposure, the charges in the photodiode 8 in row A and the photodiode 8 in row B are transferred to the V-CCD 9! After adding the electric direction of the A row and the charge of the B row, the signal is read out as an odd field signal. The detailed timing for reading is the same as for the odd field in FIG.

Next, in frame readout, until exposure, the 8th t%
Equivalent to reading out the field in (a), when reading charges, the A row of the photodiode 8 is read out in the odd field, and the B row of the photodiode 1-8 is read out in the even field. The detailed timing of reading is as shown in FIG.

Figure 9 is a sensitivity characteristic diagram of CCDI, and the horizontal axis represents the optical intensity.
The vertical axis represents the signal position level, and V SA
T represents the saturation potential, V9. A V-CCD is V-C
Represents the upper saturation degree of CD, Ll.

LSAT stands for V-CCD, respectively (to the light when the photodiode reaches its saturation potential).

Further, C1 is the output surface M of the photodiode, and c2 is a curve obtained by adding up two pixels of this.

Now, when the exposure time is made equal, field readout and frame readout are twice as sensitive as frame readout in terms of sensitivity, ie, signal level, as shown in FIG. On the other hand, since the number of pixels of the signal output in frame readout is twice as large as that in field readout, the vertical resolution is also doubled. In CCDs designed for frame readout, the V-CCD is usually made as thin as possible to improve sensitivity, and the aperture ratio of the photodiode is increased to increase the light-receiving area of the photodiode. There is. In this case, the saturation potential capacity of the V-CCD is usually not very large. Normally, the saturation potential of a V-CCD is about 1.5 times the saturation potential of a photodiode, as shown in FIG. Therefore, in the device shown in FIG. 5, when field reading is performed,
When two vertically adjacent pixels receive light amount Lh,
The sum of the charges of the photodiodes A and B exceeds the saturation potential of the V-CCD, causing blooming.

[9. Problem to be clearly solved] As described above, in conventional imaging devices, a blooming phenomenon occurs when the sum of the charges of two diodes exceeds the saturation potential of v-cco during field readout. There was.

The present invention has been made to solve such conventional problems, and has an object to prevent blooming from occurring even when field readout is performed using a transfer CCD with a low saturation potential designed for frame readout. It is an object of the present invention to provide a #M image device with a rotational speed.

[Means for Solving the Problems] In order to achieve the above-mentioned object 1.1, the imaging device of the present invention has switching operations for field readout and frame readout and i! ! means for switching the overflow level in each pixel by moving the pixel.

[Function] By having the configuration described in L, even when field reading is performed in an image sensor using a transfer CCD with a small saturation potential, the saturation potential of the transfer COD is not exceeded by controlling the overflow level. There is no blooming mink.

[Example] FIG. 10 is a diagram showing the potential distribution in the depth direction of a commonly used photodiode having a vertical overflow train.

In the figure, there is a peak of potential at ctp, and now the overflow train voltage is V. When Fo becomes Va[V], it becomes a potential mountain or Pa[V], and v O
If FD is Vb [V], the peak of potential is Pb
[V]. Therefore, the overflow train voltage V. . The lower the peak of the potential is by changing , the lower the saturation potential of the photodiode will be. Conversely, the higher the peak of the potential, the higher the saturation potential of the photodiode. Note that Va>Vb.

Using this property, the overflow train voltage V can be reduced.

By controlling 20, the saturation potential of the photodiode can be controlled. That is, the overflow train voltage is V during the frame. ,. The dynamic range can be increased by lowering the voltage, and the blooming resistance can be improved by increasing the overflow train voltage vo when in the field.

FIG. 1 is a block diagram schematically showing the main parts of an embodiment of the present invention, and the difference from FIG. 5 is a bias circuit 5.
is set to V by the system control unit 20 in response to field reading and frame reading, respectively. rn't V a
, ·vb is controlled by switching, and the other points are rotation.

Figure 2 is a sensitivity characteristic diagram of the CCD in the device shown in Figure 1.
Similar to FIG. 9, the horizontal axis shows the amount of light, and the vertical axis shows the signal potential level. That is, during field reading rather than during frame reading.

Overflow train voltage V. , by controlling the bias circuit to set D high so that it does not exceed the sum of the photodiodes of row A and row B or the saturation potential of V-CCD, without impairing the dynamic range during the frame. , it is possible to prevent blooming in the field. That is, the sensitivity characteristics can be made as shown in FIG.

FIG. 3 is a block diagram showing a specific example of a case where a memory is used in the system control unit 20 of the embodiment shown in FIG. 1, and an EEPROM 30 is included in the system control unit 20.

The potentials Va and Vb of the overflow train voltage V OF n are coated and stored in this EEPROM 30, and this information is stored in a digital-analog (D
/A) By converter 31! I can get it. To explain the operation shown in FIG. 3, when the optimum values Va and Vb of the overflow train voltage VQFO in field read and frame read are respectively stored in the EEPROM 30 and switched to field read or frame read by switch 6, ■Optimal overflow train voltage for each read mode. The value of 1o is read out from the EEPROM, converted into a voltage by the D/A converter 31, and then supplied to the bias circuit 5 and output to the CCD.
Apply to l.

By using such a means, it is possible to not only obtain the optimum overflow train voltage vnrn for CCDI regardless of field readout or frame readout, but also to
By adjusting the volume using digital data rather than adjusting the volume, it is possible to reduce the volume a, which is a very powerful means of automating the adjustment.

In the above embodiments, the train voltage of the vertical overflow train is changed as the 11th stage for controlling the overflow level, or the overflow is controlled by a pre-recombination pulse as shown in JP-A-59-153385, for example. Then, by increasing the frequency of this pulse, the overflow level is lowered, and the frequency is lowered.

[Effects of the Invention] As explained in 1-1 above, the present invention provides a means for switching the overflow level in each pixel in conjunction with the switching operation for field readout and frame readout, so dynamic accuracy is not lost during claim readout. In addition, for field readout, the image sensor can be driven under optimal conditions without impairing its anti-blooming characteristics.

Furthermore, this overflow 17 level information is stored in the EEPROM, and the optimal conditions for each overflow level are read out from the EEPROM in conjunction with switching between field readout and frame readout, and the adjustment volume is eliminated by acting as an IM image element. , it is possible to provide a device suitable for automating the adjustment process.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the main reed part of an embodiment of the present invention, FIG. 2 is a sensitivity characteristic diagram of the CCD in the device 1[A, and FIG. 3 is a system control diagram of the embodiment 11J. Block diagram showing a specific example when memory is used in the unit, No. 4
The figure shows conventional field readout and frame readout switching nf
One of the main parts of a busy imaging device! ! 5 is an IA schematically showing the CCD used in FIG. 1, FIG. 6 is a drive timing chart for field readout, FIG. 7 is a drive timing chart for frame readout, Figure 8 is a schematic diagram of the imaging sequence in an electronic still camera, Figure 9 is a sensitivity characteristic diagram of a CCD, and Figure 10 is a potential distribution in the depth direction of a commonly used vertical overflow train type photodiode. It is a diagram. In the figure. 1: ccD 2: Signal processing circuit 3 Drive circuit 4: Clock generation circuit 5: Bias circuit 20 System control section: IO: EEPROM: 11: D
/A Converter Representative Patent Attorney 1) Haruyuki Kitatake Figure 3 1υ Figure 4 Po'AIin r-x- U Figure 5 (Q) 71-+vP stirrup (b) Boom Moo vt. Figure 8

Claims (2)

[Claims] (1) A switching means for switching the signal formed in each pixel of the image sensor between field readout and frame readout, and an overflow for switching and controlling the overflow level of each pixel in conjunction with the switching operation of this switching means. An imaging device comprising a control means. (2) The imaging device according to claim 1, wherein data regarding the overflow level of each pixel in the field readout and frame readout is recorded in an EEPROM.