Solid-state imaging device and method for driving the same

Abstract: A solid-state imaging device includes a sensor portion for accumulating a signal charge produced by photoelectric conversion, a charge transfer register for transferring the signal charge, a charge/voltage converting portion connected to the charge transfer register, and a means for carrying out a shutter operation for discharging the charge accumulated by the sensor portion in synchronization with a signal charge reset period of the charge/voltage converting portion'.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a solid-state imaging device and a method for driving such a solid-state imaging device in accordance with the precharacterizing parts of independent claims 1 and 5, respectively. A solid-state imaging device and a method of driving the same are respectively known from Yoshinori Kuno et al.: "A 7K-PixelX3 Line Color Linear Sensor With Single-Side Readout Method", IEEE Transactions On Consumer Electronics, Vol. 41, No. 3, August 1, 1995, pages 436 to 440. Description of the Related Art: For example, in a color CCD linear sensor having a plurality of sensor lines it has been proposed that it is provided with a shutter function by which the amplitudes of a plurality of signals from the sensor lines can be controlled. A main purpose to use such a shutter function is, for example, in a color linear sensor having three sensor lines of R(red), G(green) and B(blue), to adjust the white balance of the output voltages from the R, G, and B sensors. If the same accumulating time is set, the magnitudes of each of the R, G, and B output voltages are different depending on their sensitivities. This leads to the difference of dynamic range in the R, G, and B output voltages. In order to cope with this problem, such a correction is performed that in the latter stage of the signal processes the output levels are arranged by varying each of the gains of R, G, B and particularly if a higher quality of an image is required, the output levels of RGB are required to be arranged before the adjustment of gain, namely, just at the CCD output. Accordingly such a method is used in which, if it is assumed that τ ROG is a period from a time when a reading gate pulse is applied to a time when the next reading gate pulse is applied, τ ROG is set to a charge accumulating period to the sensor portion (this is defined as 1H period), and then an effective accumulating period each of the R,G,B is varied by a shutter pulse input. 1H period consists of a period for transferring a signal charge, namely, an effective signal period and the subsequent non-transfer period. In a prior art, when this effective accumulating period is to be set, the input of the shutter pulse (for example, of turning the shutter pulse off) is set in the period other than the effective signal period, namely, the non-effective period. That is, if the effective signal period is set as the input period of the shutter pulse, for example, a potential of a common semi-conductor well area on a semi-conductor substrate side fluctuates as a result of the input of shutter pulse and therefore the wave form of an output signal also fluctuates owing to the influence of the coupling of shutter pulse to affect on the quality of an image. Accordingly, the input time of the shutter pulse is set in a so-called non-transfer period other than the effective signal period. However, if the input time of the shutter pulse is set in the non-transfer period other than the effective signal period, a variable range of the signal charge accumulating time is so limited that there remains no marginal time, because the shutter operation becomes in the remaining period a signal charge accumulating operation. Accordingly, if the effective accumulating time is to be set longer, the τ ROG is set as a longer time and the non-transfer period must be made long. At this time, such a drawback is produced that the signal processing time on a set increases. The solid-state imaging device known from the above document of Yoshinori Kuno et al. and representing the closest prior art in accordance with the precharacterizing parts of the independent claims discloses on its page 439 and shows its in Fig. 7 that the integration time, that is the time period from the falling edge of each shutter pulse to the falling edge of Φ ROG of each sensor is changeable. Further, this document discloses that a signal charge reset of the charge/voltage converting portion is performed in synchronization with the transfer clock which is clocked at the read-out rate and that the transfer clock period and the signal charge reset period are identical (see clocks Φ 1 , Φ 2 , and Φ RS in Fig. 7 of this document). All CCD imaging devices use this feature which is required to remove signal charge from the charge/voltage converting portion in order to prepare it for receiving the next signal charge. WO 92/06564 A discloses a solid-state imaging device in which all clock signals including the shutter signal are derived from the master clock which cycles at the read-out rate, its period thus being identical with the transfer clock period and also implicitly with the signal charge reset period. That is, the shutter operation of this known solid-state imaging device is also performed in synchronization with the signal charge reset period of the charge/voltage converting portion. SUMMARY OF THE INVENTION It is an object of the present invention to achieve a solid-state imaging device and a method of driving such a solid-state imaging device which enables the shutter operation at any time in and out the effective signal period. According to a first aspect, the present invention provides a solid-state imaging device comprising a sensor portion for accumulating a signal charge produced by photoelectric conversion, a charge transfer register for transferring said signal charge, a charge/voltage converting portion connected to said charge transfer register and having a reset gate portion and being reset when a reset pulse having a pulse duration is applied to said reset gate portion, and a means for carrying out a shutter operation for discharging a charge accumulated by said sensor portion by means of a shutter pulse signal, characterized in that said solid-state imaging device further comprises a means for applying said shutter pulse signal during the duration of said reset pulse of said charge/voltage converting portion. According to a second aspect, the present invention provides a method of driving a solid-state imaging device having a sensor portion for accumulating a signal charge generated by a photoelectric conversion, a charge transfer register and a charge/voltage converting portion connected to said charge transfer register and having a reset gate portion and being reset when a reset pulse having a pulse duration is applied to said reset gate portion, comprising the step of carrying out the shutter operation for discharging a charge accumulated by said sensor portion by means of a shutter pulse signal, characterized by the step that said shutter pulse signal is applied during the duration of said reset pulse of said charge/voltage converting portion. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a color CCD linear sensor according to the present invention; FIG. 2 is a timing chart of input pulses to the color CCD linear sensor according to the present invention; FIG. 3 is a timing chart showing examples of a reset pulse Φ RS , a shutter pulse Φ SHUT and an output wave form V OUT ; and FIG. 4 is a timing chart showing examples of the reset pulse Φ RS , the shutter pulse Φ SHUT and the output wave form V OUT according to an embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state imaging device according to the present invention comprises a sensor portion, a charge transfer register, and means for performing a shutter operation in synchronism with a reset period of a charge voltage converter portion. The solid-state imaging device according to the present invention is a linear sensor having a plurality of sensor lines and being capable of controlling the amplitude of output signals from the sensor lines by a shutter function, and a means for performing a shutter operation in each sensor line in synchronism with the reset period of the charge voltage converter portion. A method of driving a solid state image sensor according to the present invention enables to perform a shutter operation in synchronism with the reset period of the charge voltage converter portion. An embodiment of the present invention will be described below in reference with the drawings. FIG. 1 shows an embodiment of the present invention which is incorporated in a color CCD linear sensor. In FIG. 1, a color CCD linear sensor is generally designated by reference numeral 1. The color CCD linear sensor 1 is formed of a plurality of sensor lines, in this embodiment three sensor lines, which are comprised of a single linear sensor (an image element), namely, a R(red) linear sensor 2R, a G(green) linear sensor 2G and a B(blue) linear sensor 2B. The R linear sensor 2R, the G linear sensor 2G and the B linear sensor 2B have a R sensor array 3r, a G sensor array 3g and a B sensor array 3b respectively, each array including a plurality of sensor portions 3. On one sides of the sensor arrays 3r, 3g and 3b there are provided charge transfer registers (which are referred to as CCD registers) 4r, 4g and 4b, which are for example constructed as two-phase drive CCDs, via reading gate portions 5r, 5g and 5b respectively while on the other sides of the sensor arrays 3r, 3g and 3b there are provided shutter drain regions 7r, 7g and 7b via shutter gate portions 6r, 6g and 6b respectively. Adjacent to the end stage of each of the CCD registers 4r, 4g, 4b, an output gate portion 11 and a floating diffusion region 12 which becomes a charge voltage converter unit are formed and further, a reset gate portion 13 and a reset drain 14 adjoining the floating diffusion region are formed. An output circuit 15 is connected to the floating diffusion region 12. A reading gate pulse  ROG is applied to the reading gate portions 5r, 5g and 5b, a reset pulse  RS is applied to the reset gate portion 13 and a fixed voltage is applied to the output gate portion 11. Two-phase drive clock pulses  1 and  2 are applied to the CCD registers 4r, 4g and 4b and particularly a drive clock pulse  LH , which is the same as  1 , is applied to the end stage of the transfer portion. On the other hand, a shutter means is formed of each of the shutter gate portions 6r, 6g and 6b and the shutter drain regions 7r, 7g and 7b. When shutter pulses  SHUT-R ,  SHUT-G and  SHUT-B (See FIG. 2) are applied to the shutter gate portions 6r, 6g and 6b respectively, the signal charges which have been accumulated in the sensor arrays 3r, 3g and 3b are discharged to the shutter drain regions 7r, 7g and 7b via the shutter gate portions 6r, 6g and 6b respectively. As shown in FIG. 2, in this color CCD linear sensor 1, the period from the time when the reading gate pulse  ROG is applied to the time when the subsequent reading gate pulse  ROG is applied is τ ROG and this τ ROG is set as a period for accumulating the charge in the sensor portion 3 (which is defined as 1H period). This 1H period consists of an effective signal period T A for transferring and outputting the signal charge and the subsequent non-transfer period T B . In the color CCD linear sensor 1, the signal charges which have been accumulated in the respective sensor arrays 3r, 3g and 3b by means of photo-electric conversion are read simultaneously to the CCD registers 4r, 4g and 4b respectively by applying the reading gate pulse  ROG to the reading gate portions 5r, 5g and 5b. If the two-phase drive clock pulses  1 ,  2 and  LH are applied to the CCD registers 4r, 4g and 4b, the charges are transferred during the effective signal period T A of FIG. 2 and the signal charge at each one pixel (sensor portion) is read via the floating diffusion regions 12 as an output signal by the output circuit 15. The floating diffusion region 12 is reset when the reset pulse Φ RS is supplied to the reset gate portions 13 at each pixel. The non-transfer period T B from the end of the effective signal period T A and before the subsequent reading gate pulse Φ ROG is applied is a state such that no charge is transferred. Thus, according to the present embodiment, at any time during the 1H period, namely, whether during the effective signal period T A or the non-transfer period T B , the input of the shutter pulses Φ SHUT-R , Φ SHUT-G , and Φ SHUT-B can be performed. At this time, the shutter pulses Φ SHUT-R , Φ SHUT-G , and Φ SHUT-B are input during the duration T RS of the reset pulse Φ RS applied to the floating diffusion region 12 or the charge voltage converter portions. In this way, the shutter operation can be performed during the pulse duration T RS of the reset pulse Φ RS . For example, according to FIG. 3, during the duration T RS when the reset pulse Φ RS is applied in the effective signal period T A , the shutter pulse Φ SHUT is turned off. In the embodiment of FIG. 4, the shutter pulse Φ SHUT is applied during the pulse duration T RS of the reset pulse Φ RS when the reset pulse Φ RS is applied in the effective signal period T A . In the embodiment shown in FIG. 2, the shutter pulse Φ SHUT-R is not input to the R linear sensor 2R which has the lowest sensibility among the R linear sensor 2R, the G linear sensor 2G and the B linear sensor 2B, but the shutter pulses Φ SHUT-G and Φ SHUT-B are input to the G linear sensor 2G and the B linear sensor 2B respectively. In this case, the effective accumulating times of the R linear sensor 2R, the G linear sensor 2G and the B-linear sensor 2B become t R , t G , and t B respectively. In this way, if the shutter pulses Φ SHUT (Φ SHUT-G , Φ SHUT-B ) are input during the pulse duration of the reset pulse T RS , the influence of the coupling is produced only in a reset phase Re in an output wave form V OUT of FIG. 3 and FIG. 4 but no influence of the coupling is produced in a precharge phase P and a data phase D which are required in a correlation double sampling circuit (CDS) for removing noise. Accordingly, the input times of the shutter pulses Φ SHUT (Φ SHUT-R , Φ SHUT-G , and Φ SHUT-B ) can be set at any time in the 1H period whether in or out the effective signal period T A . Further, the influence of the coupling of the shutter pulses Φ SHUT on the wave form of output signal can be suppressed. In the above embodiment, the floating diffusion region is used as the charge voltage converter portion, but the floating gate or the like can be also used. In the above embodiment, the present invention is applied to the color CCD linear sensor 1 having three single linear sensors 2R, 2G and 2B but may be applied to a color CCD linear sensor having a plurality of, other than three, single linear sensors. Further, the present invention can be applied to a single color linear sensor. The present invention can also be applied to a CCD area sensor. In this case, the shutter operation is performed during the duration of a reset pulse of the charge voltage converter portion which is connected to a horizontal transfer register. According to the present invention, the influence of the coupling based on the shutter operation is not affected on the wave form of the output signal and the shutter operation can be performed at anytime of the period including the period of reading a signal. Accordingly, the variable range of the effective accumulating period by the shutter control is widened. Having described preferred embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the present invention is limited only by the features of the appended claims.

Claims: A solid-state imaging device comprising: a sensor portion (3r, 3g. 3b) for accumulating a signal charge produced by photoelectric conversion; a charge transfer register (4r, 4g, 4b) for transferring said signal charge; a charge/voltage converting portion (11 - 14) connected to said charge transfer register (4r, 4g, 4b) and having a reset gate portion and being reset when a reset pulse (Φ RS ) having a pulse duration (T RS ) is applied to said reset gate portion (13); and a means (6r, 6g, 6b) for carrying out a shutter operation for discharging a charge accumulated by said sensor portion (3r, 3g, 3b) by means of a shutter pulse signal (Φ SHUT-R , Φ SHUT-G , Φ SHUT-B ), characterized in that said solid-state imaging device further comprises a means for applying said shutter pulse signal (Φ SHUT-R , Φ SHUT-G , Φ SHUT-B ) to said means (6r, 6g, 6b) during the duration (T RS ) of said reset pulse (Φ RS ) of said charge/voltage converting portion (11 - 14). The solid-state imaging device according to claim 1, further comprising: a plurality of line sensors (2R, 2G, 2B), wherein said means (6r, 6g, 6b) for carrying out the shutter operation discharges a charge accumulated by a line sensor (2g, 2b) having a higher sensitivity as compared with a line sensor (2r) having the lowest sensitivity among those of said plurality of line sensors (2r, 2g, 2b). The solid-state imaging device according to claim 1, wherein said charge/voltage converting portion (11 - 14) comprises a floating diffusion portion (12). The solid-state imaging device according to claim 1, wherein said charge/voltage converting portion comprises a floating gate. A method of driving a solid-state imaging device having a sensor portion (3r, 3g, 3b) for accumulating a signal charge generated by photoelectric conversion, a charge transfer register (4r, 4g, 4b) and a charge/voltage converting portion (11 - 14) connected to said charge transfer register and having a reset gate portion (13) and being reset when a reset pulse (Φ RS ) having a pulse duration (T RS ) is applied to said reset gate portion (13); comprising the step of: carrying out the shutter operation for discharging a charge accumulated by said sensor portion by means of a shutter pulse signal (Φ SHUT-R , Φ SHUT-G , Φ SHUT-B ), characterized by the step that said shutter pulse signal (Φ SHUT-R , Φ SHUT-G , Φ SHUT-B ) is applied during the duration (T RS ) of said reset pulse (Φ RS ) of said charge/voltage converting portion (11 - 14). The method of driving a solid-state imaging device according to claim 5, wherein said solid-state imaging device comprises a plurality of line sensors (2R, 2G, 2B) and in said shutter operation a charge accumulated by a line sensor (2G, 2B) having a higher sensitivity as compared with a line sensor (2R) having the lowest sensitivity among those of said plurality of line sensors (2R, 2G, 2B) is discharged. The method of driving a solid-state imaging device according to claim 5, wherein said charge/voltage converting portion (11 - 14) comprises a floating diffusion portion (11). The method of driving a solid-state imaging device according to claim 5, wherein said charge/voltage converting portion comprises a floating gate. The method of driving a solid-state imaging device according to claim 5, wherein said sensor portion has a plurality of line sensors (2R, 2G, 2B) each of which has a sensor line (3r, 3g, 3b) with a plurality of sensor portions (3) for accumulating signal charges generated by photoelectric conversion, a charge transfer register (4r, 4g, 4b) for transferring said signal charges, a charge/voltage converting portion (11 - 14) respectively connected to one of said plurality of charge transfer registers (4r, 4g, 4b), a shutter gate portion (5r, 5g, 5b) respectively connected to said plurality of sensor portions (3) of each sensor line (3r, 3g, 3b) and to shutter drain regions (7r, 7g, 7b) respectively associated to each sensor line (3r, 3g, 3b).

Inventors: YOSHINORI KUNO, YOSHINORI, KUNO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1997
Main classification: H04N3
IPC codes: H01L27, H04N3, H04N5