Apparatus and method of supplying driving signals of image sensor

Abstract

An apparatus and method of supplying driving signals to an image sensor are provided. The apparatus includes a driving signal generator generating two driving signals at one of a plurality of rates, a filtering unit filtering the driving signals in response to the plurality of rates, and a selector selecting the filtering result corresponding to the rate of the driving signals from the plurality of filtering results. Accordingly, the image sensor can stable operate even when the driving signals are applied to the image sensor at various rates.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other exemplary objects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates the internal structure of a conventional image sensor;

FIG. 2 is a diagram explaining the operating principle of the image sensor;

FIG. 3 is a diagram illustrating a cross point condition that driving signals of an image sensor must satisfy according to an exemplary embodiment of the present invention;

FIGS. 4A, 4B and 4C are diagrams illustrating an operation of filtering driving signals at a high rate in order to supply the driving signals to an image sensor according to an exemplary embodiment of the present invention;

FIGS. 5A, 5B and 5C are diagrams illustrating an operation of filtering driving signals at a low rate in order to supply the driving signals to an image sensor according to an exemplary embodiment of the present invention;

FIG. 6 is a block diagram of an apparatus for supplying driving signals to an image sensor according to an exemplary embodiment of the present invention;

FIG. 7A illustrates transmission of driving signals in the apparatus for supplying the driving signals to an image sensor according to an exemplary embodiment of the present invention;

FIG. 7B is a circuit diagram of the filtering unit and the selector illustrated in FIG. 7A; and

FIG. 8 is a flow chart of a method of supplying driving signals to an image sensor according to an exemplary embodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The internal structure and the operating principle of a CCD sensor will be explained with reference to FIGS. 1 and 2. FIG. 1 illustrates the internal structure of a CCD sensor having a lead 100 and corresponding electrode 110, an n+ semiconductor layer 120 and p-type silicon substrate in which a depletion layer 130 is formed. When light is input to a photodiode, charges are generated in an n+ semiconductor layer 120 and stored in a potential well 140 under the photodiode. The potential well 140 is surrounded by left and right walls. The photodiode is reset through a pixel reset gate before an image is read. Specifically, the left wall of the photodiode is removed so that the stored charges drain out. When light is input to the photodiode after the photodiode is reset, new charges are stored in the potential well of the photodiode. The right wall of the photodiode well is removed after light is input to the photodiode, to transfer the newly stored charges to a potential well 140 of the CCD sensor. When driving signals are applied to electrode gates of the CCD sensor, the charges transferred to the CCD sensor are transferred in one direction and read. The quantity of the read charges is converted into a digital value by an analog-to-digital converter and stored in a memory.

FIG. 2 illustrates an operation of applying driving signals to electrode gates of the CCD sensor to serially read charges transferred to the CCD sensor. In FIG. 2, f1, f2 and f3 denote driving signals applied to electrodes connected to respective pixels of the CCD sensor. When a high voltage is applied to the electrodes of the respective pixels of the CCD sensor, potential wells capable of storing charges are formed under the electrodes. Reference numerals 210 through 240 represent potential wells formed in pixels of the CCD sensor with the lapse of time and charges stored in the potential wells. Referring to FIG. 2, the charges stored in the CCD sensor are transferred to the right with the lapse of time. At a time t1, the driving signals f1, f2 and f3 are at high, low and low voltages, respectively. Accordingly, a potential well is formed in the first pixel to which a high voltage is applied and charges are stored in the potential well. At a time t2, the driving signal f2 is passed to a high voltage. Thus, a potential well is formed in the second pixel so that the barrier between the first and second pixels collapses. Accordingly, the charges stored in the first pixel are transferred to the second pixel. At a time t3, the driving signal f1 is at a voltage between the high and low voltages, and thus a potential well having an intermediate potential is formed. At a time t4, the driving signal f1 is passed to a low voltage so that the potential well of the first pixel becomes shallow and the depth of the potential well of the second pixel increases. According to an exemplary implementation, all the charges stored in the first pixel are transferred to the second pixel. In this manner, the charges are sequentially transferred from the first pixel through the second pixel to the third pixel and the quantity of transferred charges is read.

There are various methods of applying the driving signals to the CCD sensor in order to transfer charges in the CCD sensor. The example illustrated in FIG. 2 is a 3-phase mode method that applies three driving signals having the same rate but different phases to the CCD sensor to drive the CCD sensor. Other methods include a method of applying two driving signals having different phases and a method of applying four driving signals having different phases.

Driving signals must be organically supplied to electrodes of the CCD sensor in order to normally operate the CCD sensor. One of conditions of organically applying the driving signals to the CCD sensor is that cross points of the driving signals must be located in a predetermined voltage range. Cross points of two predetermined driving signals among a plurality of driving signals applied to the CCD sensor having the same rate but different phases, must be located in a predetermined voltage range. In particular, cross points of two driving signals having opposite phases must be located in the predetermined voltage range. FIG. 3 illustrates driving signals that satisfy the cross point condition. Referring to FIG. 3, cross points of two driving signals with opposite phases are located in a predetermined voltage range to meet a predetermined operation specification of the CCD sensor.

Driving signals of an image sensor included in an image reading apparatus are generated in a main board. The main board of the image reading apparatus is considerably distant from the image sensor so that the driving signals are transmitted from the main board to the image sensor through a cable having a considerable length. Therefore, a large amount of noise is generated due to the cable or the board and an offset voltage is varied. Accordingly, cross points of the driving signals can only be disposed in a predetermined voltage range when the noise is removed from the driving signals and the offset voltage is adjusted. Therefore, the noise must be removed from the driving signals that have to satisfy the cross point condition. The offset voltage is also adjusted to locate the cross points in the predetermined voltage range before the driving signals are transmitted to the CCD sensor.

Noise that is generated due to the cable or the board depends on the rate of the driving signals supplied to the image sensor. FIGS. 4A and 5A illustrate waveforms of two driving signals, which are generated in a main board. The driving signals illustrated in FIG. 4A have a rate of 15 MHz, and the driving signals illustrated in FIG. 5A have a rate of 3 MHz. While the main board can generate more than two clock signals, only two predetermined clock signals among the plurality of clock signals can be filtered to meet the cross point condition and supplied to an image sensor. According to an exemplary implementation, the two clock signals should have opposite phases.

FIGS. 4B and 5B illustrate waveforms of two driving signals, which have been deformed due to overshoot, undershoot, noise and offset variations, which are generated when the driving signals are transferred through a cable. While the driving signals at 3 MHz, illustrated in FIG. 5B, only have overshoot, undershoot and a small amount of RF noise, the driving signals at 15 MHz, illustrated in FIG. 4B, have severe RF noise and offset variations in addition to overshoot and undershoot.

As described above, the degree of influence of noise on the driving signals depends on the speed of the driving signals. Accordingly, when the driving signals are filtered, noise is required to be removed and offset required to be controlled in response to the rate of the driving signals. For example, the driving signals at 3 MHz and the driving signals at 15 MHz have to be filtered by filters with different designs, respectively, in order to remove noise from the driving signals and control offset to locate cross points of the driving signals in a predetermined voltage range. If the driving signals at 15 MHz are filtered by a filter designed to filter the driving signals at 3 MHz, cross points of the driving signals at 15 Mhz are not located in the predetermined voltage range. If the driving signals at 3 MHz are filtered by a filter designed to filter the driving signals at 15 MHz, cross points of the driving signals at 3 Mhz are not located in the predetermined voltage range. Accordingly, when the driving signals have various rates, the cross points of the driving signals can be located in the predetermined voltage range and an image sensor receiving the driving signals can only be stably operated when the driving signals are filtered by a filter which is designed based on the rate of the driving signals.

A peripheral circuit for filtering the driving signals in order to locate cross points of the driving signals in a predetermined voltage range can be configured with ACT logic or with a passive element such as a resistor, an inductor or a capacitor. When the peripheral circuit is composed of a passive element, the peripheral circuit can be easily constructed at a low cost.

The configuration and operation of an apparatus for supplying driving signals to an image sensor will be explained with reference to FIG. 6. FIG. 6 is a block diagram of the apparatus for supplying driving signals to an image sensor according to an exemplary embodiment of the present invention. The apparatus for supplying driving signals to an image sensor includes a driving signal generator 600, a filtering unit 610, and a selector 620.

The driving signal generator 600 generates two driving signals with a predetermined speed among a plurality of speeds and transmits the driving signals to the image sensor. The driving signal generator 600 can be included in a main board of an image reading apparatus including the image sensor operated by the driving signals. The driving signal generator 600 can generate a plurality of clock signals that have the same speed but different phases according to a driving signal operating condition set in response to the type and driving method of the image sensor. The two driving signals can be a predetermined pair of clock signals among the plurality of clock signals generated by the driving signal generator 600. That is, the driving signal generator 600 can generate first through Nth clock signals having the same rate but different phases and transmit only a predetermined clock signal pair required to satisfy a cross point condition to the filtering unit 610 in response to the type of image sensor and driving method of the image sensor, for example, first and second driving signals.

FIG. 7A illustrates that only the first and second driving signals among the first through Nth driving signals generated by the driving signal generator 700 are transmitted to the filtering unit 710 (corresponding to the filtering unit 610 illustrated in FIG. 6) and the selector 720 (corresponding to the selector 620 illustrated in FIG. 6). FIG. 7B is a block diagram of the filtering unit 710 and the selector 720 according to an exemplary embodiment of the present invention.

Cross points of the first and second driving signals must be located in a predetermined voltage range in order to normally operate the image sensor in the driving signal supply apparatus according to an exemplary embodiment of the present invention illustrated in FIGS. 7A and 7B, and the first and second driving signals can have a rate of 15 MHz and 3 MHz.

The driving signal generator 700 generates the first through Nth driving signals at 15 MHz or 3 MHz and transmits the first and second driving signals to the filtering unit 710 through a cable. The cable filters the first and second driving signals so the first and second driving signals satisfy a cross point condition. The driving signal generator 700 directly supplies the third through Nth driving signals to the image sensor through the cable.

Waveforms of the first and second driving signals are deformed due to noise when the first and second driving signals are transmitted through the cable. The degree to which the waveforms are deformed depends on the rate of the first and second driving signals. As illustrated in FIGS. 4B and 5B, when the first and second driving signals are at 3 MHz, the waveforms of the first and second driving signals are slightly deformed due to overshoot, undershoot and small RF noise. However, when the first and second driving signals are at 15 MHz, the waveforms of the first and second driving signals are severely deformed by offset variations in addition to overshoot, undershoot and RF noise.

The filtering unit 710 filters the first and second driving signals in response to the rate of the first and second driving signals. The filtering unit 710 can filter the first and second driving signals by using a plurality of filters. The plurality of filters respectively corresponds to a plurality of rates of the plurality of driving signals generated by the driving signal generator 700. FIG. 7B illustrates a high-rate filter 711 for filtering the first and second driving signals in a high-rate mode corresponding to 15 MHz and a low-rate filter 712 for filtering the first and second driving signals in a low-rate mode corresponding to 3 MHz. According to an exemplary implementation, the filtering unit 710 includes a pair of high-rate filters 711a and 711b and a pair of low-rate filters 712a and 712b in order to respectively filter the first and second driving signals.

The high-rate filters 711a and 711b respectively remove noise from the first and second driving signals transmitted at 15 MHz and control offsets such that cross points of the filtered first and second driving signals are located in a predetermined voltage range. The low-rate filters 712a and 712b respectively remove noise from the first and second driving signals transmitted at 3 MHz and control offsets such that the cross points of the filtered first and second driving signals are located in the predetermined voltage range.

The waveforms of the first and second driving signals filtered by the high-rate filters 711a and 711b and the low-rate filters 712a and 712b depend on the rate of the first and second driving signals applied to the filtering unit 710. If the first and second driving signals are transmitted at 3 MHz to the filtering unit 710, the cross points of the first and second driving signals filtered by the low-rate filters 712a and 712b are located in the predetermined voltage range. However, the cross points of the first and second driving signals filtered by the high-rate filters 711a and 711b are not located in the predetermined voltage range.

When the first and second driving signals are transmitted at 15 MHz to the filtering unit 710, the cross points of the first and second driving signals filtered by the high-rate filters 711a and 711b are located in the predetermined voltage range. However, the cross points of the first and second driving signals filtered by the low-rate filters 712a and 712b are not located in the predetermined voltage range.

The plurality of filters that corresponds to the plurality of rates of the plurality of driving signals generated by the driving signal generator 700 respectively have filter coefficients determined by the rates of the respective filters. The filters can be configured with an active filter including a semiconductor device such as an ACT logic or a passive filter including a resistor, an inductor or a capacitor.

The selector 720 selects the first and second driving signals filtered by the filters corresponding to the rate of the first and second driving signals from the filtering results of the filtering unit 710. That is, the selector unit 720 selects the first and second driving signals filtered by the high-rate filters 711a and 711b when the first and second driving signals are transmitted at 15 MHz and selects the first and second driving signals filtered by the low-rate filters 712a and 712b when the first and second driving signals are transmitted at 3 MHz.

As illustrated in FIG. 7B, the selector 720 can be configured with first and second multiplexers 720a and 720b that receive a control signal corresponding to the rate of the first and second driving signals. The selector 720 may select the filtering results of the filters corresponding to the rate of the first and second driving signals from the filtering results of the filtering unit 710 in response to the control signal, and may output the result of the selection. According to an exemplary implementation, the control signal that corresponds to the rate of the first and second driving signals is transmitted from the driving signal generator. The first multiplexer 720a selects the filtering result of the filter corresponding to the rate of the first driving signal from the filtering results of the filtering unit 710 and the second multipelxer 720b selects the filtering result of a filter corresponding to the rate of the second driving signal from the filtering results of the filtering unit 710.

The first and second driving signals may be transmitted in two modes such as the high-rate mode and the low-rate mode. A signal at a high level is applied to control terminals CONTROL of the first and second multiplexers 720a and 720b in the high-rate mode and a signal (at a low level) is applied to the control terminals CONTROL of the first and second multiplexers 720a and 720b in the low-rate mode to control the first and second multiplexers 720a and 720b to output the filtering results corresponding to the rate of the first and second driving signals.

As described above, the driving signal supply apparatus, according an exemplary embodiment of the present invention, generates driving signals at various rates, filters the driving signals using filters that respectively correspond to the various rates, selects filtering results corresponding to the rate of the driving signals and supplies the results of the selection to the image sensor. Accordingly, even when the driving signals are applied at various rates to the image sensor, the cross points of the driving signals are located in a predetermined voltage range.

A method of supplying driving signals to an image sensor, according to an exemplary embodiment of the present invention, will now be explained with reference to FIG. 8. In step 800, driving signals for controlling a charge transfer operation of the image sensor are generated. The driving signals may be a plurality of clock signals that comprise the same rate but different phases. The plurality of clock signals are transmitted to a filtering unit through a cable.

In step 810, two predetermined clock signals having opposite phases among the plurality of clock signals transmitted to the filtering unit are filtered by filters that respectively correspond to a plurality of rates of the clock signals to remove noise from the clock signals and control offset of the clock signals.

All the clock signals can be filtered by the filtering unit and then supplied to the image sensor in order to reduce cost. However, only the two clock signals determined according to the type and driving method of the image sensor can be filtered and supplied to the image sensor to satisfy a minimum condition required to normally operate the image sensor. According to an exemplary implementation, the two clock signals are a pair of clock signals with opposite phases.

Here, the filters filter two driving signals at a plurality of rates such that cross points of the filtered driving signals are located in a predetermined voltage range. The filter coefficients of the filters are determined according to the plurality of rates. The filters can remove noise from the driving signals and control offsets of the driving signals such that cross points of the driving signal can be located in the predetermined voltage range.

In step 820, the result of a filter corresponding to the rate of the transmitted clock signals is selected from the results of the plurality of filters that respectively correspond to the plurality of rates and are supplied to the image sensor.

As described above, the apparatus and method of supplying driving signals to an image sensor, according to an exemplary embodiment of the present invention, generate two driving signals such that cross points of the driving signals satisfy a predetermined operation specification, and supply the driving signals to an image sensor comprising a simple circuit configuration without using an expensive additional circuit even when the driving signals are supplied at various rates to the image sensor. Accordingly, the image sensor can be stably operated at various speeds and reliability of images read by the image sensor can be secured.

The present invention can also be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium is a data storage device that can store data which can thereafter be read by a computer system.

Samples of the computer readable recording medium include, but are not limited to, read-only memory (ROM), random-access memory (RAM), CD-ROMs; magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet via wired or wireless transmission paths). The computer readable recording medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. Also, functional programs, codes and code segments for accomplishing the present invention can be easily construed as within the scope of the invention by programmers skilled in the art to which the invention pertains.

While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.

Claims

1. An apparatus of supplying to an image sensor driving signals for controlling a charge transfer operation of the image sensor, the apparatus comprising: a driving signal generator for generating two driving signals at one of a plurality of rates;a filtering unit for filtering the driving signals in response to the plurality of rates to generate a plurality of filtering results; anda selector for selecting a filtering result corresponding to the rate of the driving signals from the plurality of filtering results.

2. The apparatus of claim 1, wherein the driving signals correspond to a pair of clock signals comprising opposite phases selected from a plurality of clock signals comprising the same rate.

3. The apparatus of claim 1, wherein the filtering unit comprises a plurality of filters that respectively correspond to the plurality of rates.

4. The apparatus of claim 3, wherein each of the plurality of filters removes noise from driving signals at a rate corresponding to the filter and controls offsets of the driving signals so that cross points of the driving signal pair are located in a voltage range.

5. The apparatus of claim 4, wherein the plurality of filters comprise respective filter coefficients determined according to the rates of the respective filters.

6. The apparatus of claim 5, wherein the plurality of filters comprise active filters.

7. The apparatus of claim 5, wherein the plurality of filters comprise passive filters.

8. The apparatus of claim 7, wherein each of the passive filters comprises at least one of a resistor, an inductor and a capacitor.

9. The apparatus of claim 1, wherein the driving signal generator transmits the generated driving signals with information regarding the rate of the driving signals, and the selector comprises multiplexers that select filtering results corresponding to the rate of the driving signals from the plurality of filtering results in response to the information regarding the rate of the driving signals.

10. A method of supplying to the image sensor driving signals for controlling a charge transfer operation of an image sensor, the method comprising: generating two driving signals at one of a plurality of rates;filtering the driving signals in response to the plurality of rates; andselecting the filtering result corresponding to the rate of the driving signals from the plurality of filtering results.

11. The method of claim 10, wherein the driving signals correspond to a pair of clock signals comprising opposite phases selected from a plurality of clock signals comprising the same rate.

12. The method of claim 10, wherein the filtering of the driving signals comprises filtering the driving signals using a plurality of filters that respectively correspond to the plurality of rates.

13. The method of claim 12, wherein each of the plurality of filters removes noise from driving signals at a rate corresponding to the filter and controls offsets of the driving signals such that cross points of the driving signal pair are located in a voltage range.

14. A computer readable recording medium having stored thereon a computer program for executing a method of supplying driving signals for controlling a charge transfer operation of an image sensor to the image sensor, comprising: a first set of instructions for generating two driving signals at one of a plurality of rates;a second set of instructions for filtering the driving signals in response to the plurality of rates; anda third set of instructions for selecting the filtering result corresponding to the rate of the driving signals from the plurality of filtering results.

15. An apparatus for supplying driving signals to an image sensor, the apparatus comprising: a driving signal generator for generating two driving signals at one of a plurality of rates,wherein, the driving signals correspond to a pair of clock signals comprising opposite phases selected from a plurality of clock signals comprising the same rate; anda filtering unit for filtering the driving signals in response to the plurality of rates to generate a plurality of filtering results,wherein the filtering unit comprises a plurality of filters that respectively correspond to the plurality of rates.

16. The apparatus of claim 15, further comprising a selector for selecting a filtering result corresponding to the rate of the driving signals from the plurality of filtering results.

17. The apparatus of claim 15, wherein each of the plurality of filters removes noise from driving signals at a rate corresponding to the filter and controls offsets of the driving signals so that cross points of the driving signal pair are located in a voltage range.

18. The apparatus of claim 17, wherein the plurality of filters comprise respective filter coefficients determined according to the rates of the respective filters.

19. The apparatus of claim 18, wherein the plurality of filters comprise active filters.

20. The apparatus of claim 18, wherein the plurality of filters comprise passive filters.

21. The apparatus of claim 20, wherein each of the passive filters comprises at least one of a resistor, an inductor and a capacitor.

22. The apparatus of claim 15, wherein the driving signal generator transmits the generated driving signals with information regarding the rate of the driving signals, and the selector comprises multiplexers that select filtering results corresponding to the rate of the driving signals from the plurality of filtering results in response to the information regarding the rate of the driving signals.