Solid state image pickup device and its driving method using two different periods

Abstract

Incident light is photoelectrically converted in a one-unit pixel photoelectric converter section 300, while an electronic shuttering time two pixel mixture signal charge 301, a field signal charge 1 302, and a field signal charge 2 303, are transferred respectively with 8-phase clock by HCCD1 304, HCCD2 305, and HCCD3 306. After passing through a CDS & clamp circuit 307, they are subjected to a decision of signal saturation by a signal decision circuit 309. After having their outputs selected by a signal selector circuit 308, they are subjected to calculating processing in a signal processing circuit 310 to execute image signal reproduction.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a solid state image pickup device for expanding the management range in quantity of incident light to the high-luminance side and a method for driving the same, and in particular, to a solid state image pickup device for expanding the management range in quantity of incident light to the high-luminance side by setting up at least two signal charging periods in a specified period represented by the field or frame of a video signal and reproducing the signal charges in the signal charging period without using any external field memory or any frame memory and a method for driving the same.

[0003] 2. Related Art of the Invention

[0004] According to a conventional technique, at least two mutually-different charging periods are set up in one frame or one field in expanding the management range in quantity of incident light. For example, a first charging period T1 corresponding to the conventional vertical scanning period and a second charging period T2 shorter than the first charging period in the vertical blanking period are set up in one field period TF. Then a signal charge Q1 obtained in the first charging period is reproduced with a gain of 1, and a signal charge Q2 obtained in the second charging period is reproduced with a gain (T1/T2). In this place, when the signal charge Q1 reaches a saturation charge quantity, a management range in quantity of incident light being (T1/T2) times greater than the gain in the conventional case is consequently achieved by using the signal information of the signal charge Q2.

[0005] In regard to the above-mentioned element drive method for expanding the management range in quantity of incident light, there is a proposal of dispensing with any external frame memory (Japanese Patent Laid-Open Publication No. SHO 63-250980). The above-mentioned proposal describes a method for continuously transferring signal charges obtained in two charging periods dividedly provided in one field period TF in a vertical CCD by producing three signal packets with four pixels and a total of eight transfer electrodes according to the structure of the current CCD, using signal charges of a mixture of two pixels in the first charging period as two packets, and using signal charges of a mixture of four pixels in the second charging period as one packet.

SUMMARY OF THE INVENTION

[0006] However, it is required to read two times at a time interval of Δ T for the purpose of addingly mixing the signal charges of the mixture of four pixels, there exist two different types of signal charges T2 and (T2+Δ T) in an identical packet. When the signal charges of the mixture of four pixels in the two types of charging periods mutually different in time by Δ T are subjected to calculation processing with the gain of (T1/T2) without distinction, there occurs disadvantages such as misalignment in color and misalignment in luminance in adjusting the second charging period T2 according to the quantity of light of the subject.

[0007] By proposing a drive method and solid state image pickup device free of the difference Δ T between charging periods in the second charging period T2 that is problematic when signal charges are read from a photoelectric converting element to a vertical CCD at least two times in one field period, the management range in quantity of incident light can be expanded, producing neither misalignment in color nor misalignment in luminance.

[0008] The management range in quantity of incident light can be expanded to the high-luminance side without using any external field memory or any frame memory for a subject having a wide range of distribution in luminance by managing the quantity of light smaller than a standard quantity of light and the quantity of light about two times greater than the standard quantity of light with the first charging period T1 and managing a region of the subject which has comes to have a saturation charge quantity in the first charging period T1 with the second charging period T2 in the vertical blanking period.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a diagram showing a solid state image pickup device of the present invention.

[0010] FIG. 2 is a chart for explaining a first drive method of the present invention.

[0011] FIG. 3 is a diagram showing an A-field of a first drive embodiment of the present invention.

[0012] FIG. 4 is a diagram showing a B-field of the first drive embodiment of the present invention.

[0013] FIG. 5 is a diagram of an exemplified first solid state image pickup device of the present invention.

[0014] FIG. 6 is a graph for explaining the effect of the first embodiment of the present invention.

[0015] FIG. 7 is a chart for explaining a second drive method of the present invention.

[0016] FIG. 8 is a diagram of an A-field of a second drive embodiment of the present invention.

[0017] FIG. 9 is a diagram of a B-field of the second drive embodiment of the present invention.

[0018] FIG. 10 is a chart for explaining a third drive method of the present invention.

PREFERRED EMBODIMENTS

[0019] The following describes an embodiment of the present invention with reference to the drawings.

[0020] FIG. 1 shows an exemplified solid state image pickup device relevant to the claim 1 of the present invention.

[0021] Four transfer electrodes of a VCCD 110 correspond to a unit pixel 100, while eight transfer electrodes of φ V1 transfer electrode 101, φ V2 transfer electrode 102, φ V3 transfer electrode 103, φ V4 transfer electrode 104, φ V5 transfer electrode 105, φ V6 transfer electrode 106, φ V7 transfer electrode 107, and φ V8 transfer electrode 108 are used as totally eight transfer electrodes to correspond to two continuous unit pixels, when an 8-phase transfer clock is applied to them. The φ V2 transfer electrode 102 and the V6 transfer electrode 106 are each provided with a read gate 109. Although two read gates are provided for one read electrode by means of a polysilicon of the first layer, the read electrode may utilize the polysilicon of either the first layer or the second layer. It is also permitted to consider that adjoining two pixels in the direction of VCCD as one pixel in the case where the conventional CCD is used. For the element drive examples in FIG. 2 and subsequent figures, a description is provided based on the structure of FIG. 1.

[0022] FIGS. 2, 3, and 4 show embodiments relevant to the claims 2, 3, and 4 by means of the solid state image pickup device shown in FIG. 1.

[0023] FIG. 2 shows an A-FIELD 201 and a B-FIELD 203 of a normal TV frame. FIG. 2 also shows the timing of charge, read, and transfer of signals in the A-FIELD 201 and B-FIELD 203 in each odd-line pixel and each even-line pixel.

[0024] The odd-line pixel 232 and the even-line pixel 233 are preliminarily made to have coincided charge period start timing by a known electronic shuttering operation (VOD (vertical overflow drain shuttering operation) sweep).

[0025] The even-line pixel 233 obtains an even-line first signal charge 205 according to a signal input in a period T11224. An operation of read to the VCCD is executed with timing TAF1 210. Meanwhile, the odd-line pixel 232 obtains an odd-line first signal charge 206 according to a signal input in a period T12225, and an operation of read to the VCCD is executed with timing TAF21 211. Further in a V-blank period 202, the even-line pixel 233 obtains an even-line second signal charge 207 according to a signal input in a period T2227. An operation of read to the VCCD is executed with timing TAS1 212. Meanwhile, the odd-line pixel 232 obtains an odd-line second signal charge 208 according to a signal input in a period T2228 set up in an identical charging period with the period T2227, and an operation of read to the VCCD is executed with timing TAS21 213. In this place, control of the charging times in the period T2227 and the period T2228 executed for the purpose of picking up a region having a high luminance of the subject in the V-blank period 202 is executed by adjusting a VOD-sweep period 229 provided within the entire field period 226.

[0026] Although the same operation is executed in the B-FIELD 203, it is permitted to replace the charging period of an odd-line first signal charge 214 with the charging period of an even-line first signal charge 215.

[0027] FIGS. 3 and 4 show the timing of the read and transfer operations. A signal charge 240 read with the timing TAF1 210 is transferred in the VCCD by one pixel. With the timing TAF21 211, a signal charge 241 is read. In FIG. 3, twenty clock pulses are used from the timing TAF1 210 to the timing TAF21 211. Subsequently, by using twenty clock pulses from the timing TAS1 212 to the timing TAS21 213, the charging periods of T2227 and T2228 are allowed to have the same duration. Further, a signal charge 242 corresponding to the even-line second signal charge 207 and a signal charge 243 corresponding to the odd-line second signal charge 208 are mixed with each other with the timing TAS21 213 in a manner as shown in FIG. 3. There is an interval of twenty clock pulses from TAS1 212 to TAS21 213 between the periods for reading both the signal charges. Subsequently, the signal charges are transferred in the VCCD according to the 8-phase clock. Although the charging periods T2227 and T2228 have a charging period of twenty clock pulses in this example, it is of course permitted to provide no limitation on the number of clock pulses. Meanwhile, as described hereinbefore, the charging periods of T2227 and T2228 are controlled by increasing or decreasing the interval from TAF21 211 to TAS1 212, according to which the VOD-sweep period 229 is increased or decreased.

[0028] FIG. 5 shows an embodiment relevant to the claims 5, 6, and 8. FIG. 6 shows the effect of expanding the management range in quantity of incident light.

[0029] Incident light is photo-electrically converted in a one-unit pixel photoelectric converter section 300. Meanwhile, an electronic shuttering time two-pixel mixture signal charge 301, a field signal charge 1302, and a field signal charge 2303 are transferred respectively by HCCD1304, HCCD2305, and HCCD3306. After passing through a CDS & clamp circuit 307, they are subjected to decision of signal saturation by a signal decision circuit 309 based on the saturation or unsaturation condition of signals output from all or a part of the HCCD1, 2, and 3. After being further subjected to selection of output in a signal selector circuit 308, they are put to calculation processing as described hereinafter in a signal processing circuit 310 to execute image signal reproduction.

[0030] Then an exemplified image reproducing method is shown. In the following conditional expressions, VT represents a voltage corresponding to the saturation charge quantity of an element.

[0031] First, when the condition of Equation 1 is true in regard to the signal voltages V (T1) and V (T12) in the charging periods T11 and T12, the signals V (T11) and V (T12) are selected by the signal selector circuit 308. When the condition of Equation 1 is false, the signal selector circuit 308 selects the electronic shuttering time two-pixel mixture signal charge 301, while the signal voltage in the charging period T2 is converted into Vsig (T2) in a signal processing circuit 310 through calculation of Equation 2. Although a is defined by Equation 3 in this place, it is permitted to use another appropriate value, for example, the values in Equation 4. It should be noted that the other signals which have not been selected are abandoned.

[0032] Equation 1:

max (V (T11), V (T12))<VT

[0033] Equation 2:

Vsig (T2)=a×V (T2)

[0034] Equation 3:

a=T11/T2

[0035] Equation 4:

a=T12/T2

[0036] The expansion of the management range in quantity of incident light of the present embodiment will be described with reference to FIG. 6.

[0037] An output signal charge quantity obtained by the read and transfer operations through mixture of two pixels in a conventional CCD is shown as a conventional two-pixel mixture type saturation electric charge quantity 302. The saturation charge quantity of signal charges in the charging periods T11224 and T12225 shown in FIG. 2 (a) come to have a value corresponding to one transfer electrode in one unit pixel in one unit pixel 100 shown in FIG. 1, and therefore the value is one fourth of the conventional two-pixel mixture type saturation electric charge quantity. In forming a luminance signal, a signal charge 240 and a signal charge 241 are added together in an external circuit, and therefore the value is half of the conventional two-pixel mixture type saturation charge quantity. The value is shown as all pixel independent read time saturation electric charge quantity 321.

[0038] According to the element and drive method of the present embodiment, a signal charge obtained by mixing the even-line second signal charge 207 in the charging period T2227 with the odd-line second signal charge 208 in the charging period T2228 can be independently read simultaneously, and therefore an electronic shuttering tow-pixel mixing time saturation electric charge quantity 322 can be obtained. In this place, the periods T2227 and T2228 can be varied, for example, from 1/500 second to 1/2000 second to allow an effect as represented by variable 325 in FIG. 6 to be obtained. Therefore, a management incident light quantity expansion range 323 greater than a conventional management incident light quantity upper limit 324 can be achieved.

[0039] FIGS. 7, 8, and 9 show an embodiment in the case where VOD-sweep is not used. FIG. 7 shows an odd-line pixel 432 and an even-line pixel 433 as well as the timing of signal charge, read, and transfer in an A-FIELD 401 and a B-FIELD 403 of a normal TV frame.

[0040] In this case, the charging period start timings of the odd-line pixel 432 and the even-line pixel 433 differ from each other. The even-line pixel 433 obtains an even-line first signal charge 405 according to a signal input in a period T11424. An operation of read to the VCCD is executed with timing TAF1 410. Meanwhile, the odd-line pixel 432 obtains an odd-line first signal charge 406 according to a signal input in a period T12425, and an operation of read to the VCCD is executed with timing TAF21 411. Further in a V-blank period 402, the even-line pixel 433 obtains an even-line second signal charge 407 according to a signal input in a period T2427. An operation of read to the VCCD is executed with timing TAS1 412. Meanwhile, the odd-line pixel 432 obtains an odd-line second signal charge 408 according to a signal input in a period T2428 set up in an identical charging period with the period T2427, and an operation of read to the VCCD is executed with timing TAS21 413. In this place, the periods T11424 and T12425 differ from each other and also differ depending on whether they are in the A-FIELD 401 or in the B-FIELD 403. Therefore, when the periods T2427 and T2428 having the same charging time are controlled, there is a possibility of generating misalignment in color and misalignment in luminance in the period of four fields. However, the pixel data are read independently in the present invention, a calculation (Equation 6) which takes the ratio in charging period (Equation 5) into account can be allowed. Therefore, by using a value Vsig′ (T11) calculated in terms of the charging period T12, neither misalignment in color nor misalignment in luminance takes place.

[0041] Equation 5:

b=T12/T11

[0042] Equation 6:

Vsig′ (T11)=b×V (T11)

[0043] FIGS. 8 and 9 show the timing of the read and transfer operations. A signal charge 440 read with the timing TAF1 410 is transferred in the VCCD by one pixel. With the timing TAF21 411, a signal charge 441 is read. In FIG. 3, twenty clock pulses are used from the timing TAF1 410 to the timing TAF21 411. Subsequently, by aligning the timing from TAS1 412 to the timing TAS21 413 in twenty clock pulses, the charging periods in the period T2427 and T2428 are allowed to have an identical duration. Further, after a signal charge 442 corresponding to the even-line second signal charge 407 is transferred by one pixel in the period of twenty clock pulses, a signal charge 443 corresponding to the odd-line second signal charge 408 is read through superimposition with the timing TAS21 412 in a manner as shown in FIG. 3 to be mixed with the signal charge and subsequently transferred in the VCCD according to the 8-phase clock. Although the charging periods T2427 and T2428 correspond to twenty clock pulses in this example, it is of course permitted to provide no limitation on the number of clock pulses.

[0044] FIG. 10 shows a case where the charging period of an odd-line first signal charge 414 and the charging period of an even-line first signal charge 415 as shown in FIG. 7 are replaced with each other. In this place, an even-line first signal charge 505 is a signal charge obtained from a signal input in a period T11524. An operation of read to the VCCD is executed with timing TAF1 510. An odd-line first signal charge 506 is a signal charge obtained from a signal input in a period T12525, and an operation of read to the VCCD is executed with timing TAF2 511. An even-line second signal charge 507 is a signal obtained from a signal input in a period T2527. An operation of read to the VCCD is executed with timing TAS1 512. An odd-line second signal charge 508 is a signal obtained from a signal input in a period T2528, and an operation of read to the VCCD is executed with timing TAS2 513.

[0045] In the present invention, the periods T11524 and T12525 can be set up at an identical duration, the conversion of Equation 6 is not necessary.

[0046] As described above, in the present invention, the management range in quantity of incident light can be expanded to the high-luminance side without using any field memory or any frame memory.

Claims

1. A solid state image pickup device ,wherein one unit pixel is composed of an input signal converting section and CCD electric charge transfer means, the input signal converting section is provided with at least one opening region for receiving light, the input signal converting section is arranged in an X-Y two-dimensional array form, a transfer electrode of the CCD electric charge transfer means provided in Y-direction adjacent to the input signal converting section has such electrodes constitution that four electrodes are provided for the one unit pixel, and totally eight electrodes are provided for two unit pixels continuous in the Y-direction, and the eight transfer electrodes are driven by an 8-phase transfer clock pulse generated by a pulse generating circuit.

2. In a solid state image pickup device drive method; in a specified period represented by a field or frame of a video signal, with regard to a first pixel and a second pixel constituting two continuous unit pixels in a Y-direction, a first A signal charging period and a second A signal charging period shorter in time than the first A signal charging period are set up for the first pixel, and a first B signal charging period and a second B signal charging period shorter in time than the first B signal charging period are set up for the second pixel, and when a start timing of the second A signal charging period is same as the start timing of the second B signal charging period, or even when they are different each other, the second A and second B signal charging periods have an identical duration.

3. A solid state image pickup device drive method as claimed in claim 2, wherein the second A and second B signal charging periods are controlled by effecting an electronic shuttering operation in the specified period represented by the field or frame of the video signal.

4. A solid state image pickup device drive method as claimed in claim 2 or 3, wherein among a first A signal charge obtained in the first A signal charging period, a second A signal charge obtained in the second A charging period, a first B signal charge obtained in the first B charging period, and a second B signal charge obtained in the second B charging period, the second A signal charge and the second B signal charge are read as a second AB signal charge by being mixed with each other, and the three signal charges of the first A, first B, and second AB signal charges are read independently.

5. A solid state image pickup device as claimed in claim 1, wherein the each sections are formed integratedly.

6. A solid state image pickup device drive method as claimed in claim 4, wherein the second AB signal charge is read by a first HCCD, the first A signal charge is read by a second HCCD, and the first B signal charge is read by a third HCCD to an external signal processing circuit in a same horizontal scanning period.

7. A solid state image pickup device drive method as claimed in claim 4, wherein the second AB signal charge is read by a first HCCD, and the first A signal charge and the first B signal charge are read by a second HCCD to an external signal processing circuit in a same horizontal scanning period.

8. A solid state image pickup device as claimed in claim 1 or 5 comprising: a signal decision circuit which is provided for HCCD output terminals and makes a decision of signal saturation based on a saturation or unsaturation condition of signals outputted from all or a part of signal output terminals, and a signal selection circuit for selecting between the outputs of the HCCD output terminals according to a decision made by the signal decision circuit.