Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-09-27
2001-01-09
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C348S280000, C348S311000
Reexamination Certificate
active
06172352
ABSTRACT:
FIELD OF INVENTION
The present invention relates to monochrome and color scanning systems and more particularly relates to a scanning mechanism for producing multiple outputs in parallel from corresponding multiple sensing segments and combining the multiple outputs thereafter to increase signal readout rate from the scanning mechanism.
DESCRIPTION OF THE RELATED ART
There are many applications that need optical scanners to convert paper-based objects, such as texts and graphics, to an electronic format that can be subsequently analyzed, distributed and archived. One of the most popular optical scanners is flatbed scanners that convert objects, including pictures and papers, to images that can be used, for example, for building Web pages and optical character recognition. Another emerging optical scanner is what is called sheet-fed scanners that are small and unobtrusive enough to sit between a keyboard and a computer monitor or integrated into a keyboard to provide a handy scanning means. Most optical scanners are referred to as image scanners as the output thereof is generally in digital image format.
An image scanner generally includes a sensing module that converts scanning objects optically into electronic images. The sensing module comprises an illumination system, an optical system, an image sensor and an output circuit. The illumination system is used to illuminate an object that is being scanned. The optical system is used to direct and focus the light reflected from the scanning object onto the image sensor. The image sensor comprises a plurality of photodiodes or photocapacitors, referred to as photodetectors hereafter, that are sensitive to light and produce proportional pixel signals accordingly. Therefore corresponding pixel signals are produced in the image sensor when the reflected light is focused thereon and the output circuit is used to convert the pixel signals to an appropriate format to be processed or stored in subsequent systems.
The image sensor is generally in the form of Complementary Metal-Oxide Semiconductor (CMOS) or charged couple device (CCD) and fabricated in either a one-dimensional array or two-dimensional array. The operation of the image sensor often comprises two processes, the first being the light integration process and the second being the readout process. In the light integration process, each photodetector captures the incident photons of the reflected light and records the total amount of these photons as a charge or pixel signal. After the light integration process the photodetector is masked so that no further photons are captured and meanwhile the photodetectors start the readout process during which the pixel signal stored in each photodetector is individually readout, via a readout passage, to a data bus or video bus. The readout passage is an intermediate process that transports the pixel signals to the data bus. To be more specific, in the case of CMOS, the readout passage is a switch array comprising a plurality of readout switches, each responsible for coupling one of the photodetectors to the data bus. The pixel signals in the photodetectors are readout, by turning on sequentially the readout switches, to the data bus. If there are N photodetectors in the image array, hence N readout switches in and readout passage, and it takes one clock cycle of a sensor clock signal to turn on one switch and read out one pixel signal onto the data bus, it will consequently take N clock cycles of the sensor clock signal to read out all of the N pixel signals. In the case of CCD, the readout passage is a shift register. The shift register comprises the same number of memory cells as the number of photodetectors in the image sensor, each memory cell holding one pixel signal from a respective photodetector. The pixel signals are dumped into the shift register coupled thereto in parallel. Then the pixel signals in the shift register are serially shifted out, one pixel at a time from one memory cell to another, from the register into the data bus. In other words, if there are N photodetectors in the image array and it takes one clock cycle to read out one pixel signal, it will then take N clock cycles of the sensor clock signal to read out all of the N pixels. In reality, N is generally a large number and the readout time is proportional to N. To increase the pixel signal readout, an often used approach is to increase the clock cycle of the sensor clock signal.
Many flatbed and sheet-fed scanners use one-dimensional image sensor. This requires either the image sensor or the scanning object to move against each other so as to get the scanning object completely scanned. If the scanning object is a piece of paper having the standard size of 8.5 inch by 11 inch and the resultant image resolution is 300 dot-per-inch (dpi), N will be required to be at least 2550 or larger if the paper margins are considered. When the scanners are capable of reproducing color, the same scanning object has to be scanned multiple times, the readout time can be much prolonged. For example, a contact image sensor module SV351A4C from Scan Vision Inc. takes 1.5 msec to scan a line of 9 inch wide at 300 dpi for a gray image but 7.5 mesc to scan the same for a color image. If a scanning object has a long size, the time accumulated for a whole image thereof can be significant. Although the readout time may be reduced by increasing the clock cycle of the sensor clock signal, the readout speed is eventually limited by the internal mechanism of the readout passage. It is well understood in semiconductors that a large number of readout switches in parallel inherently form a capacitor with large capacitance, which significantly retards the charging speed in a following signal amplifier when the pixel signals are readout to be strengthened by the signal amplifier. Similarly a large number of memory cells in a shift register may cause the pixel signals to degrade in shifting from one memory cell to another. There is thus a great need for a sensing module that can accommodate a sensor clock signal having higher clock cycle to increase the readout rate without demanding for costly high speed image sensors.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above described problems and has particular applications to high-resolution scanners. The disclosed invention yields significant improvement in the pixel readout time when a high clock cycle signal is applied to produce a high-resolution image of scanning objects. Current marketed scanners begin to experience noticeable delay when the image resolution reaches a certain value in spite of high clock cycle signal applied due to the internal mechanism of the readout passage in the sensing module. The sensing module in the present invention uses a number of readout passages in parallel to concurrently produce several segmented outputs from the image sensor and subsequently combines the outputs to produce an interleaved scanning signal under a sequence of control signals derived from the sensor clock signal. The composition of the several parallel segmented outputs using the timing in the sensor clock signal is a radical shift from the traditional readouts in image sensing module and imposes no additional demand for an even higher sensor clock signal while the signal readout rate thereof is significant increased.
The disclosed sensing module comprises an image sensor generating pixel signals, a number of readout passages to generate segmented scanning signals from the pixel signals, a multiplexer to combine the segmented scanning signals and a timing control circuit that generates a number of control signals derived from a sensor clock signal. The image sensor comprises a plurality of photodetectors and is preferably equally divided into virtual groups; pixel signals in each of the virtual groups are readout by one of the readout passages concurrently. According to one aspect of the present invention, the readout passages are switch arrays coupled to local video buses, each of the switch arrays having
Allen Stephone B.
Syscan Inc.
Zheng Joe
LandOfFree
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