CCD linear sensor

Abstract: The present invention intends to improve a difference between signal levels of odd-numbered pixels and even-numbered pixels in a CCD (charge coupled device) linear sensor. In a CCD linear sensor comprising a sensor region (1) having an array of a plurality of sensor elements (pixels) (S₁), (S₂), ... and first and second horizontal transfer registers (4) and (5) disposed on the respective sides of the sensor region (1) through read-out gate sections (2) and (3) wherein signal charges of every other sensor elements (S₁), (S₃), (S₅), ... are transferred by the first horizontal transfer register (4) while signal charges of remaining every other sensor elements (S₂), (S₄), (S₆) are transferred by the second horizontal transfer register (5), the first and second horizontal transfer registers (4) and (5) include first and second transfer electrodes (22R₁), (22R₂) to which two-phase drive pulses (H₁) and (H₂) are applied, respectively and electrode configurations at the read-out gate section side are formed substantially the same,whereby the capacity of a first transfer section (HR₁) to which the drive pulse (H₁) is applied is made equal to that of a second transfer section (HR₂) to which the drive pulse (H₂) is applied.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a solid state imaging device. Such a solid state imaging device is known from IEEE Transactions on Consumer Electronics, vol. 36, no. 3, August 1990, pages 473 - 477. Description of the Prior Art: CCD linear sensors transfer signal charges of odd- and even-numbered sensor elements (pixels) through two charge transfer registers, respectively and output the thus transferred signal charges from an output terminal of the final stage in order to improve the resolution. FIG. 1 of the accompanying drawings shows an overall structure of a conventional CCD linear sensor (the details of this structure are not described or shown in the above IEEE-Transactions). Referring to FIG. 1, first and second horizontal transfer registers 4 and 5 of CCD structure are disposed through read-out gate sections 2 and 3 on both sides of sensor region 1 in which a plurality of sensor elements (pixels) S (S 1 , S 2 , S 3 , ...) are arrayed in one direction, whereby signal charges of the odd-numbered sensor elements S 1 , S 3 , S 5 , ... are read out to the first horizontal transfer register 4 while signal charges of the even-numbered sensor elements S 2 , S 4 , S 6 , ... are read out to the second horizontal transfer register 5. Then, the respective signal charges are transferred to one direction by two-phase drive pulses ΦH1 and ΦH2 shown in FIGS. 2A and 2B. Transfer sections HR 1 and HR 2 of the final stages of the first and second horizontal transfer registers 4 and 5 are connected to a floating diffusion region 7 through a common horizontal output gate section 6 to which there is applied a gate voltage V HOG . Then, signal charges from the first and second horizontal transfer registers 4 and 5 are alternately transferred to the floating diffusion region 7, whereby they are converted into signal voltages and signals corresponding to the odd-numbered and even-numbered pixels which are alternately output from an output amplifier 8 as shown in a waveform of an output of the CCD. In the output section, the signal charges transferred to the floating diffusion region 7 are sequentially drained out through a reset gate section 9 to a reset drain region 10 by a reset pulse RG which is higher in frequency than the drive pulses H 1 and H 2 as shown in FIG. 2C. FIG. 3 of the accompanying drawings shows an enlarged plan view of the conventional first and second horizontal transfer registers 4 and 5. The first and second horizontal transfer registers 4 and 5 respectively comprise a plurality of transfer sections HR (HR 1 , HR 2 ) having transfer electrode sets 13R (13R 1 , 13R 2 ), each set having a storage electrode 12S (12S 1 , 12S 2 ) made of a polycrystalline silicon first layer and a transfer electrode 12T (12T 1 , 12T 2 ) made of a polycrystalline silicon second layer. The drive pulse H 1 is applied to every other one of the transfer electrode sets 13R 1 and the drive pulse H 2 is applied to remaining every other one of the transfer electrode sets 13R 2 . When signal charges of the sensor elements S are read out to the first and second horizontal transfer registers 4 and 5, the signal charges are read out to the region (so-called storage section) of the first storage electrode 12S 1 through the region (so-called transfer section) of the first transfer electrode 12T 1 to which the drive pulse H 1 is applied. Hence, as shown in FIG. 3, the first transfer electrodes 12T 1 to which the drive pulse H 1 is applied are shaped as a comb whose respective one ends are coupled continuously. The coupled portions thereof are provided so as to overlap the read-out gate sections 2 and 3. On the other hand, the second transfer electrodes 12T 2 to which the drive pulse H 2 is applied are disposed between the first transfer electrodes 12T 1 , and the corresponding storage electrodes 12S 1 and 12S 2 are disposed between the adjacent transfer electrodes 12T 1 and 12T 2 . In the above-mentioned CCD linear sensor, since the pattern configurations of the first and second transfer electrodes 12T 1 and 12T 2 are different, the first and second transfer electrode sets 13R 1 and 13R 2 in the horizontal transfer registers 4 and 5 are different in area. As a result, a capacity of the first transfer section HR 1 to which the drive pulse H 1 is applied and that of the second transfer section HR 2 to which the drive pulse H 2 is applied do not become equal to each other, thereby a difference being produced between the signal level of the odd-numbered pixel (sensor element) and that of the even-numbered pixel (sensor element). More specifically, in the output section, the floating diffusion region 7 is formed within the well region and the well region is interconnected to the ground. In that case, however, the capacities of the transfer sections HR 1 and HR 2 are large so that, when the horizontal transfer registers 4 and 5 are driven by the two-phase drive pulses H 1 and H 2 , a potential (known as "reference potential") Vo of the well region is momentarily fluctuated at the negative-going edges t 1 , t 2 , t 3 , ... of the drive pulse H 1 or H 2 which is used to transfer the signal charge to the floating diffusion region 7, as shown in FIG. 2. As a result, a noise component 16 is mixed into the output signal due to the fluctuation component 15. If the fluctuated component 15 of the potential Vo in the well region is the same, then no problem will occur. However, since the first and second transfer sections HR1 and HR2 are different in capacity, the output signal has different noise components 16, thereby causing a difference (so-called DC level difference) to occur between the signal level of the odd-numbered pixel and that of the even-numbered pixel. This signal level difference becomes conspicuous as the CCD linear sensor is increased in resolution. Hence, this signal level difference must be corrected at every pixel. The above mentioned IEEE Transactions Document is silent on details on the transfer electrode structure used in the shift register. JP-A-58-098 961 and its Abstract from PAJ (Publication date 13.6.1983) describes and shows in Fig. 3 a solid state imaging device comprising a sensor region formed by a plurality of elements 12a ... 12h arranged in a line, first and second read out gate sections 13 arranged between the sensor region and first and second charge transfer shift registers, the first register which has first and second electrodes 14a and 16a to which two-phase drive pulses Φ1, Φ2 are respectively applied is arranged to transfer signal charges of every other sensor elements 12a, 12c, 12e, 12g in said plurality of sensor elements, the second register having third and fourth transfer electrodes 14b and 16b to which said two-phase drive pulses Φ1, Φ2 are respectively applied is arranged in association with said sensor elements to transfer the charges of the remaining other sensor elements 12b, 12d, 12f, 12h, the first transfer electrodes 14a to which the one drive pulse Φ1 is applied and the second transfer electrodes 16a to which the other drive pulse Φ2 is applied are respectively formed in an comb-like shape and arranged opposite to one another so that their teeth are staggered and are further arranged at the side of the first read-out gate section and have the same electrode configuration. Further, the third transfer electrodes 14b to which the one drive pulse Φ1 is applied and the fourth transfer electrodes 16b to which the other drive pulse Φ2 is applied also have a comb-like shape and are arranged opposite to one another wherein their teeth are staggered at the side of the second read-out gate section and have the same electrode configuration. OBJECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide a CCD (charge coupled device) linear sensor in which the foresaid shortcomings and disadvantages encountered with the prior art can be eliminated. More specifically, it is an object of the present invention to provide a CCD linear sensor which can improve a difference between signal levels. Another object of the present invention is to provide a CCD linear sensor which can provide the image quality of high resolution without correcting a black signal. As an aspect of the present invention there is provided a solid state imaging device comprising: (a) a sensor region formed of a plurality of sensor elements arrayed in one direction; and (b) first and second charge transfer shift registers disposed on respective sides of said sensor region, and first and second read-out gate sections are arranged between said sensor region and said first and second charge transfer shift registers, respectively, said first charge transfer shift register having first and second transfer electrodes to which two-phase drive pulses are respectively applied is arranged in association with said sensor elements to transfer signal charges of every other sensor elements in said plurality of sensor elements, and said second charge transfer shift register having third and fourth transfer electrodes to which said two-phase drive pulses are applied is arranged in association with said sensor elements to transfer signal charges of remaining every other sensor elements in said plurality of sensor elements, wherein the first transfer electrodes to which the one drive pulse is applied and the second transfer electrodes to which the other drive pulse is applied are arranged at the side of said first read-out gate section, and the third transfer electrodes to which the one drive pulse is applied and the fourth transfer electrodes to which the other drive pulse is applied are arranged at the side of said second read-out gate section, characterized in that said first, second, third and fourth transfer electrodes have identical shape and the same electrode configuration (claim 1). Depending claims 2 to 6 are respectively specifying advantageous developments thereof. Therefore, a difference between the signal level corresponding to the odd-numbered pixel and the signal level corresponding to the even-numbered pixel can be improved and hence the image quality of high resolution can be obtained without correcting a black signal. The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description of an illustrative embodiment thereof to be read in conjunction with the accompanying drawings, in which like reference numerals are used to identify the same or similar parts in the several views. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a whole structure of a CCD linear sensor according to the prior art; FIGS. 2A through 2E are respectively waveform diagrams of drives pulses, a reset pulse, an output of CCD and a reference potential to which references will be made in explaining the conventional CCD linear sensor according to the prior art; FIG. 3 is a fragmentary, enlarged plan view of a main portion of a CCD linear sensor according to the prior art; and FIG. 4 is a fragmentary, enlarged plan view illustrating a main portion of a CCD linear sensor according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A CCD linear sensor according to an embodiment of the present invention will now be described with reference to FIG. 4. Referring to FIG. 4, a sensor region depicted by reference numeral 1 is formed of an array of a plurality of sensor elements S (S 1 , S 2 , ...) First and second horizontal transfer registers 4 and 5, each of which is formed of a CCD, are respectively disposed on the respective sides of the sensor region 1 through read-out gate portions 2 and 3 in parallel to the sensor region 1. The first and second horizontal transfer registers 4 and 5 are respectively formed of a plurality of transfer sections HR (HR 1 , HR 2 ) which are composed of sets of storage electrodes 21S (21S 1 , 21S 2 ) made of a polycrystalline silicon first layer and transfer electrodes 21T (21T 1 , 21T 2 ) made of a polycrystalline silicon second layer. Every other first transfer electrode sets 22R 1 are coupled to a bus line 24 to which the drive pulse H 1 is applied, while remaining every other second transfer electrode sets 22R 2 are coupled to a bus line 25 to which the drive pulse H 2 is applied. The first transfer sections HR 1 of the first horizontal transfer register 4 and to which the drive pulse H 1 is applied are formed in association with, for example, odd-numbered sensor elements S 1 , S 3 , S 5 , ... of the sensor region 1, while the first transfer sections HR 1 of the second horizontal transfer register 5 and to which the drive pulse H 1 is applied are formed in association with, for example, even-numbered sensor elements S 2 , S 4 , S 6 , ... According to this embodiment, the first transfer electrode 21T 1 to which the drive pulse H 1 is applied and the second transfer electrode 21T 2 to which the drive pulse H 2 is applied are arranged in the same electrode configuration including the configurations at the sides of the read-out gate sections 2 and 3. Parts of the respective transfer electrodes 21T 1 and 21T 2 are formed so as to overlap the corresponding read-out gate sections 2 and 3, and storage electrodes 21S 1 , and 21S 2 of the same electrode configuration are respectively formed between adjacent transfer electrodes 21T 1 and 21T 2 . Though not shown, channel stop regions are formed between the respective sensor elements S 1 , S 2 , S 3 , ... and the second transfer section HR 2 in such a fashion that signal charges of the sensor elements S 1 , S 2 , S 3 , ... are read out to the first transfer sections HR 1 of the corresponding horizontal transfer registers 4 and 5 to which the drive pulse H 1 is applied and are not transferred to the second transfer sections HR 2 to which the drive pulse H 2 is applied. When the bus line 24 to which the drive pulse H 1 is applied is disposed in the outside and the bus line 25 to which the drive pulse H 2 is applied is disposed in the inside at the side of the first horizontal transfer register 4, the bus line 24 to which the drive pulse H 1 is applied is disposed in the inside and the bus line 25 to which the drive pulse H 2 is applied is disposed in the outside at the side of the second horizontal transfer register 5. In this CCD linear sensor 26, similarly as described above, signal charges of the odd-numbered sensor elements S 1 , S 3 , S 5 , ... are read out through the read-out gate section 2 to the underside of the storage electrode 21S 1 of each first transfer section HR 1 of the first horizontal transfer register 4, while signal charges of the even-numbered sensor elements S 2 , S 4 , S 6 , ... are read out through the read-out gate section 3 to the underside of the storage electrode 21S 2 of each first transfer section HR 1 of the second horizontal transfer register 5. Then, respective signal charges are transferred in one direction within the first and second horizontal transfer registers 4 and 5 and charge-voltage-converted in the floating diffusion region 7 in the output section having a similar structure to that of FIG. 1, whereafter it is output from the output amplifier 8. According to the embodiment of the present invention, since the first transfer electrode 21T 1 to which the drive pulse H 1 is applied is divided so as to correspond to each first transfer section HR 1 , the electrode configuration of the second transfer electrode 21T 2 to which the drive pulse H 2 is applied is formed the same as that of the first transfer electrode 21T 1 and the second transfer electrode 21T 2 is formed so as to overlap the read-out gate sections 2 and 3 similarly to the first transfer electrode 21T 1 , the areas of the first and second transfer electrode sets 22R 1 and 22R 2 can be made equal to each other and the capacities of the first and second transfer sections HR 1 and HR 2 can be made equal to each other. Consequently, the fluctuation components 15 of the potential (reference potential) Vo of the well region at negative-going timing points t 1 , t 2 , t 3 ,... of the drive pulse H 1 or H 2 become substantially equal and the noise component 16 applied to the respective signals of the odd-numbered and even-numbered pixels become uniform. Therefore, a difference between the signal levels of the odd-numbered and even-numbered pixels can be improved and the image quality of high resolution can be obtained without correcting a black signal. While the signal charges of the first and second horizontal transfer registers 4 and 5 are alternately transferred to and mixed together in the floating diffusion region 7 as described above, the present invention is not limited thereto and such a variant is also possible. That is, a transfer section of several bits may be disposed at the front stage of the floating diffusion region 7 and signal charges from the first and second horizontal transfer registers 4 and 5 are alternately transferred to this transfer section of several bits, in which they are mixed together. According to the CCD imaging device, i.e., CCD linear sensor of the present invention, a difference between the signal level corresponding to the odd-numbered pixel and the signal level corresponding to the even-numbered pixel can be improved and hence, the image quality of high resolution can be obtained without correcting the black signal.

Claims: A solid state imaging device comprising: (a) a sensor region (1) formed of a plurality of sensor elements (S 1 , S 2 , ...) arrayed in one direction; and (b) first and second charge transfer shift registers (4, 5) disposed on respective sides of said sensor region (1), and first and second read-out gate sections (2, 3) are arranged between said sensor region and said first and second charge transfer shift registers (4, 5), respectively, said first charge transfer shift register (4) having first and second transfer electrodes (21T 1 , 21T 2 ) to which two-phase drive pulses (Φ H1 , Φ H2 ) are respectively applied is arranged in association with said sensor elements to transfer signal charges of every other sensor elements (S 1 , S 3 , S 5 ,...) in said plurality of sensor elements, and said second charge transfer shift register (5) having third and fourth transfer electrodes (21T 1 , 21T 2 ) to which said two-phase drive pulses (Φ H1 , Φ H2 ) are applied is arranged in association with said sensor elements to transfer signal charges of remaining every other sensor elements (S 2 , S 4 , S 6 ,...) in said plurality of sensor elements, wherein the first transfer electrodes (21T 1 ) to which the one drive pulse (Φ H1 ) is applied and the second transfer electrodes (21T 2 ) to which the other drive pulse (Φ H2 ) is applied are arranged at the side of said first read-out gate section (2), and the third transfer electrodes (21T 1 ) to which the one drive pulse (Φ H1 ) is applied and the fourth transfer electrodes (21T 2 ) to which the other drive pulse (Φ H2 ) is applied are arranged at the side of said second read-out gate section (3), characterized in that said first, second, third and fourth transfer electrodes have identical shape and the same electrode configuration. The solid state imaging device according to claim 1, wherein said first and second transfer electrodes (21T 1 , 21T 2 ) partly overlap said first read-out gate section (2). The solid state imaging device according to claim 1, wherein said third and fourth transfer electrodes (21T 1 , 21T 2 ) partly overlap said second read-out gate section (3). The solid state imaging device according to claim 1, wherein storage electrodes (21S 1 , 21S 2 ) each having the same electrode configuration are respectively formed between adjacent transfer electrodes (21T 1 , 21T 2 ). The solid state imaging device according to claim 1, wherein outputs of said first and second charge transfer shift registers (4, 5) are supplied through an output gate section (6) to a floating diffusion section (7) in which they are mixed together. The solid state imaging device according to claim 5, wherein said floating diffusion section (7) is connected through a reset gate section (9) to a reset drain region (10).

Inventors: HIRAMA MASAHIDE, HIRAMA, MASAHIDE, Hirama, Masahide, c/o Sony Corporation
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: H01L27
IPC codes: H01L27, H04N5, H04N1