Solid state imaging device with horizontal transfer paths and a driving method therefor

Abstract

In a solid state imaging device, signal charges are branched to be output to in the form of one or plural outputs. At a horizontal transfer speed not lower than a predetermined transfer speed, the imaging device transfers signal charges of color attributes classified by a branching section, to plural horizontal transfer paths, where the signal charges are converted into analog voltage signals, which will be output synchronously. At a horizontal transfer speed lower than the predetermined transfer speed, the analog voltage signal converted is output from, e.g. the horizontal transfer path which has been selected. Output amplifiers arranged on the horizontal transfer paths are differentiated in sensitivities in detecting signal charges, depending on color attributes of signal charges supplied, and output the analog voltage signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic block diagram showing a preferred embodiment of a two-line readout CCD implemented as a solid state imaging device according to the present invention;

FIG. 2 is a schematic block diagram showing a preferred embodiment of a digital camera employing the solid state imaging device of FIG. 1;

FIG. 3 is a schematic block diagram showing drivers shown in FIG. 2;

FIG. 4, part (A) is a partial plan view looked from above, and showing the schematic constitution of a horizontal transfer path in the solid state imaging device of FIG. 1, part (B) is a cross-sectional view of the transfer path, taken along a section line IV-IV, and parts. (C) and (D) show how the potential changes in various parts of the horizontal transfer path;

FIG. 5 is a timing chart showing the timing of drive signals supplied to respective electrodes of FIG. 4, parts (A) and (B);

FIG. 6, part (A) continuing from the lower part of FIG. 4 is a cross-sectional view of the transfer path, and parts (B), (C) and (D) show how the potential changes;

FIG. 7, part (A) is a partial plan view, looking from above, showing the schematic constitution of the horizontal transfer path in the device of FIG. 1, part (B) is a cross-sectional view of the transfer path, taken along a section line VII-VII, and parts (C) and (D) show how the potential changes in various parts of the horizontal transfer path;

FIG. 8, part (A) continuing from the lower part of FIG. 7 is a cross-sectional view of the transfer path, and parts (B), (C) and (D) show how the potential changes;

FIGS. 9A to 9E are schematic views for illustrating the transfer of signal charge with color attributes over horizontal transfer paths in the solid state imaging device of FIG. 1;

FIGS. 10A and 10B schematically show the difference in gate capacitances in the output amplifier of FIG. 1;

FIGS. 11A and 11B schematically show the difference in film thickness formed in the floating diffusion in the output amplifier of FIG. 1;

FIGS. 12A and 12B schematically show the difference in the surface area in the floating diffusion in the output amplifier of FIG. 1;

FIGS. 13A and 13B schematically show the presence and the absence of a film formed in the floating diffusion in the output amplifier of FIG. 1, respectively;

FIG. 14 is a partial plan view of an array of offset pixels and color filter segments in the solid state imaging device of FIG. 1;

FIGS. 15 and 16 are timing charts showing re-arraying of signal charges of the first and second fields during the horizontal blanking period in connection with horizontal transfer of the device of FIG. 14, respectively;

FIG. 17 is a timing chart showing the relationship of the drive signals supplied for the first field and the output signals in connection with horizontal transfer of the device;

FIG. 18 is a timing chart showing the relationship of low-speed readout drive signals ad output signal in the horizontal transfer of the device;

FIG. 19 is a schematic block diagram showing a three-line readout solid state imaging device applied to the imaging unit of FIG. 2;

FIG. 20 is a timing chart showing the relationship between the drive signals and the output signals as applied to the horizontal transfer for the device of FIG. 19;

FIG. 21 is a schematic block diagram showing a four-line readout solid state imaging device applied to the imaging unit of FIG. 2;

FIG. 22 is a timing chart showing the relationship between the drive signals and the output signals as applied to the horizontal transfer for the device of FIG. 21;

FIG. 23 is a schematic block diagram showing an alternative embodiment of a solid state imaging apparatus according to the present invention;

FIG. 24 is a timing chart useful for understanding an operational sequence of horizontal transfer consistent with horizontal timing signals of the initial driving condition at the time of high speed driving in the solid state imaging device of FIG. 1;

FIG. 25 is a timing chart useful for understanding an operational sequence of horizontal transfer consistent with horizontal timing signals of the inverted-branching driving condition at the time of high speed driving in the device of FIG. 1;

FIG. 26 is a timing chart also useful for understanding an operational sequence of horizontal transfer at the time of low-speed driving in the device of FIG. 1;

FIG. 27 schematically shows signal charges being transferred responsive to the horizontal timing signals of the initial driving condition at the time of transfer efficiency measurement on the horizontal transfer path in the device of FIG. 1:

FIG. 28 schematically shows signal charges being transferred responsive to the horizontal timing signals of the inverted-branching driving condition at the time of transfer efficiency measurement on the horizontal transfer path in the device of FIG. 1;

FIG. 29 is a graph showing the relationship between the quantity of residual transfer charges and the quantity of reference signals on two branching transfer paths in the device of FIG. 1:

FIG. 30 is a graph showing the relationship between the transfer efficiency and the quantity of the reference signals;

FIG. 31 is a timing chart useful for understanding the operational sequence of mixing of horizontal pixels on a horizontal transfer path before branching in the device of FIG. 1;

FIGS. 32A through 32I showing how the potential level changes which is formed in the respective transfer elements by horizontal pixel mixing on the horizontal transfer path before branching in the device of FIG. 1;

FIGS. 33 and 34 are block diagrams schematically showing changes in the output destination, consistent with the transfer efficiency on the branching horizontal transfer paths in the device of FIG. 1;

FIG. 35 schematically shows horizontal transfer paths in the device of FIG. 1, looked from above;

FIG. 36, parts (A) and (B) are a schematic plan view and a schematic cross-sectional view of one of the horizontal transfer paths shown in FIG. 35, respectively;

FIG. 37, parts (A) and (B) are a schematic plan view and a schematic cross-sectional view of the other of the horizontal transfer paths shown in FIG. 35, respectively;

FIG. 38 is a timing chart showing the timing of drive signals supplied to the respective electrodes shown in FIG. 35;

FIG. 39 is a schematic potential diagram showing the state of transfer of signal charges on the horizontal transfer path in FIG. 36;

FIG. 40 is a schematic potential diagram showing the state of transfer of signal charges on the horizontal transfer path in FIG. 37;

FIGS. 41A to 41E schematically show the state of transfer of signal charges on the horizontal transfer path in FIG. 35;

FIG. 42 is a schematic timing chart showing an example of the timing of drive signals supplied to the respective electrodes shown in FIG. 35;

FIG. 43 is a schematic timing chart showing another example of the timing of drive signals supplied to the respective electrodes shown in FIG. 35;

FIG. 44 is a flowchart useful for understanding illustrative processing for calculating the transfer efficiency;

FIGS. 45 and 46 schematically show illustrative processing for calculating the transfer efficiency on one and the other of the horizontal transfer paths, respectively;

FIG. 47 is a graph schematically showing the residual charge quantities detected from one reference signal to another;

FIG. 48 is a graph schematically showing the transfer efficiency calculated from the residual signal quantities shown in FIG. 47;

FIG. 49 is a flowchart showing illustrative processing of calculating the transfer efficiency by the processing sequence shown in FIG. 44 and for setting a variable value of the duty cycle using the transfer efficiency calculated;

FIG. 50 is a block diagram schematically showing a further alternative embodiment of a digital camera employing the device of FIG. 1;

FIG. 51 is a plan view looked from above, showing a horizontal transfer path in the device of FIG. 1;

FIG. 52 is a partial cross-sectional view showing essential part of a horizontal transfer path of FIG. 51;

FIG. 53 is a partial plan view of an array of offset pixels and color filter segments as applied to the device of FIG. 1;

FIGS. 54A through 54E and 55A through 55E schematically show transfer of signal charges R and B, and signal charges G on the horizontal transfer path of FIG. 1, respectively;

FIG. 56 is a timing chart showing the supply timing of drive signal to the electrode of FIG. 51;

FIGS. 57A through 61B schematically show the potential levels generated on the horizontal transfer path when the drive signal shown in FIG. 56 is applied;

FIG. 62 is a timing chart showing the timing of drive signals supplied to the electrodes of FIG. 55 on transferring the signal charge G;

FIGS. 63A through 64B schematically show the potential level generated on applying the drive signal shown in FIG. 62;

FIGS. 65 and 66 are timing charts showing drive signals for providing the same color of the signal charges output from the same output amplifier in the first and second lines; and

FIGS. 67A to 67E schematically illustrate the transfer of signal charges G in two horizontal transfer paths.

Claims

1. A solid state imaging device including: a two-dimensional array of photosensitive cells supplied with incident light from a field being imaged, via color filter segments for color separating the incident light, said photosensitive cells transducing the light transmitted through said color filter segments into electrical signals depending on a volume of transmitted light, the signal charges having color attributes, said device reading out from each of said photosensitive cells and transferring in a vertical direction;a first horizontal transfer circuit for transferring signal charges in a horizontal direction perpendicular to the vertical direction;a branching circuit arranged adjacent to an output end of said first horizontal transfer circuit for transiently holding the signal charges transferred and for distributing the signal charges to a plurality of output destinations related with the color attributes of the signal charges;a plurality of second horizontal transfer circuits connected to said branching circuit as branching destinations; anda plurality of output circuits each provided at an output end of each of said second horizontal transfer circuits, said output circuits each converting the signal charges into an analog voltage signal responsive to the amount of the signal charges to output the analog voltage signal;the signal charges supplied to said branching circuit at a horizontal transfer speed during horizontal transfer not lower than a preset transfer speed being classified depending on the color attributes and transferred to each of said second horizontal transfer circuits, said output circuits each converting the signal charges into said analog voltage signals;the analog voltage signals being output from selected second horizontal transfer circuit during horizontal transfer speed lower than said preset transfer speed, said output circuit converting the signal charges into said analog voltage signals;said plural output circuits exhibiting differential detection sensitivities for the signal charges depending on the color attributes of the signal charges supplied;said output circuits outputting the analog voltage signals.

2. The solid state imaging device in accordance with claim 1, wherein each of said output circuits includes an amplifier circuit for amplifying said analog voltage signals, said amplifier circuits having differential gate capacitances from each other.

3. The solid state imaging device in accordance with claim 1, wherein each of said output circuits includes a floating diffusion layer for converting the signal charges into said analog voltage signals, said output circuits having differential surface areas of said floating diffusion layers from each other.

4. The solid state imaging device in accordance with claim 1, wherein at least one of said output circuits includes a floating diffusion layer for converting the signal charges into said analog voltage signals, a nitride layer provided on the surface of said floating diffusion layer, the nitride film formed on each of said output circuits having differential thickness from each other.

5. The solid state imaging device in accordance with claim 4, wherein at least one of said plural output circuits is not provided with said floating diffusion layer.

6. A method for driving a solid state imaging device for transferring signal charges having color attributes, comprising the steps of: preparing a solid state imaging device which includes:a plurality of vertical transfer circuits for reading out signal charges having color attributes from each of photosensitive cells adapted for transducing incident light into an electrical signal, said vertical transfer circuits transferring the read-out signal charges having the color attributes in the vertical direction,a horizontal transfer circuit for transferring the signal charges transferred from said vertical transfer circuits, in the horizontal direction, anda plurality of horizontal transfer circuits branched from a transfer region adapted for branching the signal charges supplied from said horizontal transfer circuit, the signal charges having color attributes, said plural horizontal transfer circuits having differential detection sensitivities to the signal charges having the color attributes;classifying the signal charges, supplied to said branching transfer region with high speed driving with the horizontal transfer speed not less than a preset transfer speed, according to the color attributes, sending the signal charges of the color attributes on each of said plural horizontal transfer circuits, converting the signal charges of the color attributes into analog voltage signals, and outputting the analog voltage signals;sending the signal charges on selected horizontal transfer circuit with low speed driving at a horizontal transfer speed lower than the predetermined transfer speed the signal charges, converting the signal charges into analog voltage signals, and outputting the analog voltage signals from the selected horizontal transfer circuit; andchanging the phase of a driving pattern in horizontal transfer, before branching, with respect to the driving in at least one branched horizontal transfer, and adjusting the branched output destination of the signal charges having color attributes.

7. The method in accordance with claim 6 wherein in said solid state imaging device said horizontal transfer circuit before branching is set as a first horizontal transfer circuit, one of said plural horizontal transfer circuits having the detection sensitivity for the signal charges having color attributes higher than a predetermined detection sensitivity is set as second horizontal transfer circuit, one of said plural horizontal transfer circuits having the detection sensitivity for the signal charges having color attributes lower than the predetermined detection sensitivity is set as third horizontal transfer circuit; said method further comprising the step of transferring green signal charges on said second horizontal transfer circuit and red and blue signal charges on said third horizontal transfer circuit at high speed driving.

8. The method in accordance with claim 6 wherein in said solid state imaging device said horizontal transfer circuit before branching is set as a first horizontal transfer circuit, one of said plural horizontal transfer circuits having the detection sensitivity for the signal charges having color attributes higher than a predetermined detection sensitivity is set as a second horizontal transfer circuit, one of said plural horizontal transfer circuits having the detection sensitivity for the signal charges having color attributes lower than the predetermined detection sensitivity is set as a third horizontal transfer circuit; said method further comprising the step of transferring red and blue signal charges on said second horizontal transfer circuit and green signal charges on said third horizontal transfer circuit at high speed driving.

9. The method in accordance with claim 7 further comprising the steps of: transferring green signal charges on said second horizontal transfer circuit and transferring red and blue charges on said third horizontal transfer circuit, by the high speed driving in a first driving mode; andtransferring red and blue signal charges on said second horizontal transfer circuit and transferring green charges on said third horizontal transfer circuit, by the high speed driving in a second driving mode.

10. The method in accordance with claim 7 wherein the first driving mode is an automatic exposure mode or an automatic focusing mode, and the second driving mode is a mode other than the first mode.

11. The method in accordance with claim 6 further comprising the step of selecting said horizontal transfer circuit having detection sensitivity not lower than a predetermined detection sensitivity for signal charges having color attributes with the low speed driving to transfer signal charges.

12. The method in accordance with claim 6 further comprising the step of selecting said horizontal transfer circuit having detection sensitivity lower than a predetermined detection sensitivity for signal charges having color attributes with the low speed driving to transfer signal charges.

13. The method in accordance with claim 6 wherein in said solid state imaging device said horizontal transfer circuit before branching is set as a first horizontal transfer circuit, one of said plural horizontal transfer circuits having the detection sensitivity for the signal charges having color attributes higher than a predetermined detection sensitivity is set as a second horizontal transfer circuit, one of said plural horizontal transfer circuits having the detection sensitivity for the signal charges having color attributes lower than the predetermined detection sensitivity is set as a third horizontal transfer circuit; said method further comprising the steps of:selecting the horizontal transfer circuit used, depending on whether or not a selected sensitivity is not lower than the detection sensitivity;driving said third horizontal transfer circuit at a high sensitivity as the selected sensitivity not lower than the predetermined detection sensitivity; anddriving said second horizontal transfer circuit at a low sensitivity as the selected sensitivity lower than the predetermined detection sensitivity.

14. The method in accordance with claim 11 further comprising the steps of: independently controlling power supply used for driving said plural horizontal transfer circuits; andinterrupting the power supply used for driving horizontal driving circuit excluding horizontal transfer circuit used for the low speed driving.

15. The method in accordance with claim 6 wherein in said solid state imaging device said horizontal transfer circuit before branching is set as a first horizontal transfer circuit, said solid state imaging device including three horizontal transfer circuits as said plural horizontal transfer circuits; said three horizontal transfer circuits setting the, detection sensitivity of the signal charges having color attributes in three stages;said method classifying the signal charges having color attributes in the high speed driving according to the color attributes and transfers the signal charges classified.

16. The method in accordance with claim 6 wherein in said solid state imaging device said horizontal transfer circuit before branching is set as a first horizontal transfer circuit, said solid state imaging device including four horizontal transfer circuits as said plural horizontal transfer circuits; said four horizontal transfer circuits setting the detection sensitivities for the signal charges having color attributes in three stages, setting charge the detection sensitivities for green signal charge neighboring to red color and green signal charge neighboring to red color to the same charge detection sensitivity different from the remaining two sensitivities;said method further comprising the step of classifying the signal charges having color attributes in the high speed driving according to the color attributes and transfers the signal charges classified.

17. A solid state imaging apparatus including a solid state imaging device, said solid state imaging device including: a plurality of photosensitive cells arrayed in a matrix of rows and columns for photo-electrically transducing incident light from a field being imaged into signal charges;a plurality of color filter segments arranged in register with said photosensitive cells for color separating the incident light into plural colors to cause the light of the plural colors to be incident on said photosensitive cells;vertical transfer circuits for vertically transferring the signal charges read out from said photosensitive cells;a first horizontal transfer circuit for receiving the signal charges vertically transferred from said vertical transfer circuits to transfer the received signal charges horizontally;a branching circuit arranged at an output end of said first horizontal transfer circuit for distributing the horizontally transferred signal charges to an optional one of a plurality of output destinations;second and third transfer circuits for receiving the signal charges distributed from said branching circuit to further horizontally transfer the signal charges; andfirst and second output circuits arranged at output ends of said second and third transfer circuits, respectively;said solid state imaging apparatus comprising a transfer efficiency measuring circuit for measuring a transfer efficiency on said second and third transfer circuits in the course of transfer of the signal charges from said branching circuit through said second and third transfer circuits to said first and second output circuits;the driving start time of a first drive signal for driving said first horizontal transfer circuit or a second drive signal for driving said second and third horizontal transfer circuits being changed depending on a result of measurement by said transfer efficiency measuring circuit;one of said second and third horizontal transfer circuits being preferentially used to transfer the signal charges.

18. The solid state imaging apparatus in accordance with claim 17 wherein one of said second and third horizontal transfer circuits which has a higher transfer efficiency is preferentially used.

19. The solid state imaging apparatus in accordance with claim 18 wherein, in measuring the transfer efficiency, a light source of a predetermined light volume is shot beforehand at a time of shipment from a manufacturer to generate an imaging signal for measurement; said transfer efficiency measuring circuit measuring the transfer efficiency by the manufacturer using the imaging signal for measurement.

20. The solid state imaging apparatus in accordance with claim 19 wherein, when said apparatus measures the transfer efficiency, said vertical transfer circuits transfer a repetition of sets, each composed of a predetermined number of signal charges arrayed in a horizontal direction, to said first horizontal transfer circuit; said first horizontal transfer circuit during a horizontal blanking period generating said set by mixing the predetermined number of signal groups from set to set to generate a reference signal pixel and by arraying two or more void pixels deprived of signal charges by the mixing, in rear of the reference signal pixel; said first horizontal transfer circuit accumulating the signal charges transferred from said vertical transfer circuits in said first horizontal transfer circuit according to a horizontal pixel mixing system;said apparatus horizontally transferring the signal charges on said first horizontal transfer circuit to said branching circuit responsive to the first drive signal having an initial driving condition, in order to obtain a first imaging signal for measurement based on an imaging signal acquired from said first and second output circuits;said apparatus horizontally transferring the signal charges in said first horizontal transfer circuit to said branching circuit responsive to the first drive signal having a inverted-branching driving condition, in order to obtain a second imaging signal for measurement based on an imaging signal acquired from said first and second output circuits;said transfer efficiency measuring circuit measuring the transfer efficiency of said second and third horizontal transfer circuits based on the first and second imaging signals for measurement.

21. The solid state imaging apparatus in accordance with claim 20 wherein said transfer efficiency measuring circuit sets the first void pixel in the first imaging signal for measurement, as a residual charge quantity during transfer from said branching circuit to said second horizontal transfer circuit, sets the second void pixel, as a residual charge quantity during horizontal transfer on said second horizontal transfer circuit; and determines the transfer efficiency on said second transfer circuit from the reference signal pixel and the residual charge quantities; said transfer efficiency measuring circuits setting the first void pixel in the second imaging signal for measurement, as a residual charge quantity during transfer from said branching circuit to said third horizontal transfer circuit, setting the second void pixel, as a residual charge quantity during horizontal transfer on said third horizontal transfer circuit; and determining the transfer efficiency on said third transfer circuit from the reference signal pixel and the residual charge quantities.

22. The solid state imaging apparatus in accordance with claim 20 wherein said horizontal pixel mixing system is a horizontal eight-pixel mixing system.

23. The solid state imaging apparatus in accordance with claim 18 wherein, when said apparatus drives said solid state imaging device to effect two-line outputting, said branching circuit alternately distributes the signal charges transferred from said first horizontal transfer circuit, to said second and third transfer circuits, and transfers the signal charges thereon; said first and second output circuits synchronously outputting the signal charges transferred from said second and third horizontal transfer circuits;said apparatus directly using a first drive start time in an initial driving condition of the first drive signal, responsive to the measured results, when said second transfer circuits is preferentially used, said branching circuit initially transferring the signal charges to said second transfer circuit;said apparatus using a time corresponding to the first driving start time shifted relatively from a driving start time of the second drive signal, as a driving start time in a driving condition of inverted branching of the first drive signal, in case said third transfer circuit is preferentially used, said branching circuit then effecting inverted branching to transfer the signal charges initially to said third transfer circuit.

24. The solid state imaging apparatus in accordance with claim 23 wherein, when horizontal transfer on said solid state imaging device is effected at a high speed for two-line outputting, the frequency of the second drive signal is set to one-half of that of the first drive signal.

25. The solid state imaging apparatus in accordance with claim 23 wherein the plural colors are three primary colors of red, green and blue; said photosensitive cells acquiring light of the incident light indicating red, green and blue colors from said color filter segments for photo-electrically transducing the light into the signal charges of red, green and blue;said first horizontal transfer circuit horizontally transferring signal charges of red, green and blue colors vertically transferred from said vertical transfer circuits;said branching circuit transferring signal charges of red and blue colors to one of said second and third horizontal transfer circuits which is preferentially used;said branching circuit transferring signal charges of green color to the other horizontal transfer circuits.

26. The solid state imaging apparatus in accordance with claim 25 wherein one of said first and second output circuits outputs a green color signal based on the green signal charges and the other output circuit outputs red and blue signals based on the red and blue signal charges; said first and second output circuits outputting the signals to first and second output parts;said apparatus including a green color input part for receiving the green color signal and a red/blue color input part for receiving the red/blue signal, from said solid state imaging device;said first and second output circuits including first and third connecting parts connecting to said green color input part and a second input part for connecting to said red/blue input part;said first output part being connected to said second connecting part and said second output part being connected to said third connecting part, when the red and blue signal charges are output from said first output circuit with use preferentially of said second horizontal transfer circuit;said first output part being connected to said first connecting part and said second output part being connected to said second d connecting part, when the red and blue signal charges are output from said second output circuit with use preferentially of said third horizontal transfer circuit.

27. The solid state imaging apparatus in accordance with claim 26 wherein said first and second output parts and said first, second and third connecting parts are connected without wiring intersection.

28. The solid state imaging apparatus in accordance with claim 26 wherein said first and second output parts and said first, second and third connecting parts are bonding pads.

29. The solid state imaging apparatus in accordance with claim 18 wherein, when the solid state imaging device is driven by one-line outputting, said branching circuit transfers the signal charges transferred from said first horizontal transfer circuit, to only one of said second and third horizontal transfer circuits; andeither of said first and second output circuits which the signal charges are transferred to from said second or third horizontal transfer circuit outputs the signal charges;said apparatus directly using the initial driving condition of the first drive signal, in case said second horizontal transfer circuits is preferentially used, responsive to said measured results, said branching circuit then transferring the signal charges only to said second horizontal transfer circuits;said apparatus setting a driving condition of inverted branching, by inverting the phase of the first drive signal from that in the initial driving condition, or by inverting the phase of the second drive signal, in case said third horizontal transfer circuits is preferentially used;said branching circuit then inverting the branching by using the driving condition of inverted branching to transfer the signal charges only to said third horizontal transfer circuits.

30. The solid state imaging apparatus in accordance with claim 29 wherein, when horizontal transfer of said solid state imaging device is effected at low speed to execute one-line outputting, said apparatus sets the first and second drive signals to the same frequency.

31. The solid state imaging apparatus in accordance with claim 29 wherein, when horizontal transfer of said solid state imaging device is effected to execute one-line outputting, the operation of the output circuit connected to one of said second and third horizontal transfer circuits which is not preferred is halted.

32. A method for driving a solid state imaging device in which incident light from a field being imaged is separated by a color filter into a plurality of colors; the incident light passed through said color filter is photo-electrically transduced by a plurality of photosensitive cells arrayed in a matrix of rows and columns, to generate signal charges;the signal charges read out from said photosensitive cells are vertically transferred in a vertical transfer step;the signal charges vertically transferred from said vertical transfer step are received in a first horizontal transfer step and transferred horizontally;the signal charges horizontally transferred from said first horizontal transfer step are distributed to a plurality of output destinations by a branching step receiving an output of said first horizontal transfer step;the signal charges distributed from said branching step are received by second and third horizontal transfer steps and horizontally transferred further; andin second and third output steps receiving outputs of said second and third horizontal transfer steps, signals corresponding to the signal charges are output;said method comprising:a transfer efficiency measuring step of measuring the transfer efficiencies of said second and third horizontal transfer steps throughout the transfer of the signal charges from said branching step through said second and third horizontal transfer steps to said first and second output steps;the driving start time of the first drive signal which is used in said first horizontal transfer step or the driving start time of the second drive signal which is used in said second and third horizontal transfer steps being varied responsive to the results of measurement in said transfer efficiency measuring step, one of said second and third horizontal transfer steps being preferentially used, transferring the signal charges.

33. A solid state imaging apparatus including a solid state imaging device, said solid state imaging device including: a plurality of photosensitive cells arrayed in a matrix of rows and columns for photo-electrically transducing incident light from a field being imaged into signal charges;vertical transfer circuits for vertically transferring the signal charges read out from said photosensitive cells;a first horizontal transfer circuit for receiving the signal charges vertically transferred from said vertical transfer circuits to transfer the received signal charges horizontally;a branching circuit arranged at an output end of each of said first horizontal transfer circuit for distributing the horizontally transferred signal charges to any one of a plurality of output destinations;second and third transfer circuits for receiving the signal charges distributed from said branching circuit to further horizontally transfer the signal charges; andfirst and second output circuits arranged at output ends of said second and third horizontal transfer circuits, respectively, for generating electrical signals from the signal charges;said apparatus comprising a pre-branching transfer circuit arranged directly upstream of said branching circuit in said first horizontal transfer circuit for transferring the signal charges transferred by said first horizontal transfer circuit to said branching circuit;at least either one of a duty cycle and a period of the drive signal driving said pre-branching transfer circuit being changed to provide for transfer time from said pre-branching transfer circuit to said branching circuit longer than a usual transfer time.

34. The solid state imaging apparatus in accordance with claim 33 wherein at least either one of the duty cycle and the period of the drive signal driving at least one of said second and third horizontal transfer circuits is varied to provide for transfer time from said branching circuit to one of said second and third horizontal transfer circuits longer than the usual transfer time.

35. The solid state imaging apparatus in accordance with claim 33 further comprising a plurality of color filter segments arranged in register with said photosensitive cells for color separating the incident light into three primary colors of red, green and blue to cause the light of the respective colors to be incident on said photosensitive cells, wherein said photosensitive cells acquiring the incident light indicating red, green or blue colors, as primary colors, from said color filter segments, photo-electrically transduce the light into the signal charges of red, green or blue colors;said branching circuit transferring signal charges of the red and blue colors to second horizontal transfer circuits and transferring the green signal charges to said third horizontal transfer circuits;at least either one of the duty cycle and the period of the drive signal driving said pre-branching transfer circuit being changed to provide for transfer time of the red and blue color signal charges from said pre-branching transfer circuit to said branching circuit longer than the usual transfer time.

36. The solid state imaging apparatus in accordance with claim 35 wherein at lease either one of the duty cycle and the period of said drive signal driving at least one of said second and third horizontal transfer circuits is changed to provide for transfer time of said red and blue signal charges from said branching circuit to said second horizontal transfer circuits longer than the usual transfer time.

37. The solid state imaging apparatus in accordance with claim 33 further comprising a temperature detector for detecting a temperature of said solid state imaging device; wherein in case the temperature detected by said temperature detectors is lower than a predetermined value, the transfer time is set to a longer time.

38. The solid state imaging apparatus in accordance with claim 33 further comprising a temperature detector for detecting a temperature of said solid state imaging device; wherein in case the temperature detected by said temperature detectors is higher than a predetermined value, the transfer time is set to a usual value.

39. The solid state imaging apparatus in accordance with claim 33 further comprising a color temperature detector for detecting a color temperature of a field being imaged; said transfer time being made longer in case the color temperature as detected by said color temperature detector is higher or lower than a predetermined range.

40. The solid state imaging apparatus in accordance with claim 33 wherein the transfer time is made longer in case of higher sensitivity.

41. The solid state imaging apparatus in accordance with claim 33 wherein said transfer time is made a usual transfer time at a time of low speed driving.

42. The solid state imaging apparatus in accordance with claim 33 further comprising a signal processing circuit for removing the noise in the electrical signals by a correlated double sampling system; wherein a phase of a sampling pulse used in the correlated double sampling system is changed in case the transfer time is changed.

43. The solid state imaging apparatus in accordance with claim 33 further comprising a transfer efficiency calculator for calculating the transfer efficiency; wherein at lease either one of the duty cycle and the period for providing for longer transfer time is determined responsive to the transfer efficiency calculated by said transfer efficiency calculator.

44. The solid state imaging apparatus in accordance with claim 43 wherein when said transfer efficiency calculator calculates the transfer efficiency, said vertical transfer circuits transfer a signal charge set composed of a predetermined number of horizontally arrayed signal charges, to said first horizontal transfer circuit;said first horizontal transfer circuit mixing said predetermined number of signal charges by a horizontal pixel mixing system to generate a reference signal pixel and first and second void pixels deprived of signal charges by mixing, the first and second void pixels being arrayed next to the trailing end of said reference signal pixel;said branching circuit branching the reference signal pixel, said first void pixel and said second void pixel to transfer the reference signal pixel and the second void pixel to one of said second and third horizontal transfer circuits and to transfer the first void pixel to the other of said second and third horizontal transfer circuits;said transfer efficiency calculator calculating the transfer efficiency using the residual charge quantity detected from the first and second void pixels.

45. The solid state imaging apparatus in accordance with claim 44 wherein said transfer efficiency calculator calculates the transfer efficiency between said branching circuit and the horizontal transfer circuits, on which the reference signal is transferred, using the residual charge quantity as detected from said first void pixel;at lease either one of the duty cycle and the period for providing for longer transfer time being determined based on the transfer efficiency.

46. The solid state imaging apparatus in accordance with claim 44 wherein the horizontal pixel mixing system is a horizontal eight pixel mixing system.

47. The solid state imaging apparatus in accordance with claim 44 wherein in calculating the transfer efficiency, a light source of a predetermined light volume is shot beforehand at the time of shipment from a plant and the reference pixel, the first void pixel and the second void pixel are generated using signal charges obtained by the shooting;said transfer efficiency calculator calculating the transfer efficiency using the reference pixel, the first void pixel and the second void pixel;at lease either one of the duty cycle and the period for providing for longer transfer time being determined depending on the transfer efficiency determined based on the transfer efficiency calculated by said transfer efficiency calculator.

48. A method for driving a solid state imaging device in which incident light from a field being imaged is photo-electrically transduced by a plurality of photosensitive cells arrayed in a matrix of rows and columns, to generate signal charges; the signal charges read out from said photosensitive cells are vertically transferred in a vertical transfer step;the signal charges vertically transferred from said vertical transfer step are received in a first horizontal transfer step and transferred horizontally;the signal charges horizontally transferred from said first horizontal transfer step are distributed to a plurality of output destinations by a branching step receiving an output of said first horizontal transfer step;the signal charges distributed from said branching step are received by second and third horizontal transfer steps and horizontally transferred further; andin second and third output steps receiving outputs of said second and third horizontal transfer steps, respectively, the signals corresponding to the signal charges are output;said method comprising a pre-branch transfer step receiving an output of said first horizontal transfer step for transferring the signal charges transferred from said first horizontal transfer step to said branching step;at lease either one of a duty cycle and a cycle of the drive signal which is used in said pre-branch transfer step being changed to provide for transfer time of the signal charges in said transfer step longer than a usual transfer time.

49. A solid state imaging apparatus comprising: a color filter for color separating the incident light from a field being viewed into a plurality of colors;a plurality of photosensitive cells for photo-electrically transducing the light transmitted through said color filter, said photosensitive cells being arranged in register with the colors;a first transfer circuit for transferring signal charges read out from said photosensitive cells in a first direction;a second transfer circuit for transferring signal charges transferred in said first transfer circuit in a second direction;a branching circuit arranged at an output end of said second transfer circuit for distributing the signal charges transferred to a plurality of output destinations;a plurality of third transfer circuits connected as the output destinations to said branching circuit; andoutput circuits connected to an output end of said third transfer circuits;said plural colors being divided into a plurality of groups;said second transfer circuit, said branching circuit and said third transfer circuits transferring signal charges read out from the photosensitive cells related with colors of the same group, and subsequently transferring signal charges read out from the photosensitive cells related with colors of a different group or groups.

50. The solid state imaging apparatus in accordance with claim 49 wherein the plural colors are three colors of red, green and blue, and the groups are two groups, one being a group composed of red and blue and the other being a group composed of green.

51. The solid state imaging apparatus in accordance with claim 49 wherein, in case there are a plurality of colors belonging to one of said groups, the signal charges read out from the photosensitive cells related with the colors are transferred using a plurality of said third transfer circuits; in case there is one color belonging to one of said groups, the signal charges read out from the photosensitive cells related with the color being transferred using a specified one of said third transfer circuits.

52. The solid state imaging apparatus in accordance with claim 49 wherein, in case there are a plurality of colors belonging to one of said groups, the signal charges read out from the photosensitive cells related with said colors are transferred using a plurality of said third transfer circuits; in case there is one color belonging to one of said groups, the signal charges read out from the photosensitive cells related with the color being also transferred using a plurality of said third transfer circuits.

53. The solid state imaging apparatus in accordance with claim 51 wherein, in case there are a plurality of colors belonging to one of said groups, the signal charges read out from the photosensitive cells related with the colors are transferred using a specified one of said third transfer circuits from one color to another.

54. The solid state imaging apparatus in accordance with claim 49 further comprising a correction circuit for correcting the difference in characteristics among said output circuits.

55. The solid state imaging apparatus in accordance with claim 54 further comprising: a holding circuit for holding data for correcting the difference in characteristics among said output circuits;said correction circuit correcting the difference in characteristics using data owned by said holding circuit.

56. The solid state imaging apparatus in accordance with claim 49 wherein said first transfer circuit transfer the signal charges, read out from the photosensitive cells, related with the color belonging to the same group, to said second transfer circuit, and subsequently transfer signal charges read out from the photosensitive cells related with the color belonging to the different group.

57. An imaging method comprising the steps of: color-separating incident light from a field being imaged by a color filter;photo-electrically transducing the light transmitted through said color filter by a plurality of photosensitive cells related with the colors;transferring signal charges read out from said photosensitive cells by first transfer circuit in a first direction;transferring the signal charges transferred by said first transfer circuits, by a second transfer circuit in a second direction;distributing the signal charges transferred to a plurality of output destinations, by a branching circuit arranged at an output end of said second transfer circuit; andoutputting the signal charges by a plurality of third transfer circuits, connected as output destinations to said branching circuit, and by output circuits arranged at an output end of said third transfer circuits;said plural colors being grouped into a plurality of groups; andsaid second transfer circuit, said branching circuit and the third transfer circuits transferring the signal charges read out from the photosensitive cells related with the color belonging to the same group, and subsequently transferring signal charges read out from the photosensitive cells related with the color belonging to the different group.

58. An imaging method comprising the steps of: color-separating incident light from a field being imaged by a color filter;photo-electrically transducing the light transmitted through said color filter by a plurality of photosensitive cells related with the colors;transferring signal charges read out from said photosensitive cells by first transfer circuit in a first direction;transferring the signal charges, transferred by said first transfer circuit, by a second transfer circuit in a second direction; andoutputting signal charges via an output circuit arranged at an output end of said second transfer circuit;said plural colors being grouped into a plurality of groups; andsaid second transfer circuits transferring the signal charges read out from the photosensitive cells related with the color belonging to the same group, and subsequently transferring signal charges read out from the photosensitive cells related with the color belonging to the different group.