Read-out circuit for active matrix imaging arrays

Details Read-out circuit for active matrix imaging arrays Read-out circuit for active matrix imaging arrays

1997-12-02

2001-10-09

Garber, Wendy R. (Department: 2612)

Television

Camera, system and detail

Solid-state image sensor

C348S302000, C348S304000

Reexamination Certificate

active

06300977

ABSTRACT:

FIELD OF THE INVENTION
This invention relates in general to imaging arrays, and more particularly to improved read-out circuitry which, in one application, reduces the number of source or gate lines in the array, and in another application increases the dynamic range for read-out without reducing the number of source or gate lines.
BACKGROUND OF THE INVENTION
Imaging arrays are known in the art which comprise a transducer for either directly converting incident radiation to electrical charges, or for converting incident radiation to light energy (i.e. photons) and then converting the light energy to electrical charges. It is also known in the art to connect an active matrix read-out array to such prior art transducers, for collecting charges generated by the transducer onto individual pixels of the active matrix array, and then reading out the pixel charges on a row-by-row basis. The charge signals read out of the array are then measured using charge amplifiers connected to each source or data line. Examples of such prior art systems are disclosed in W. Zhao and J. A. Rowlands, “A Large Area Solid-State Detector for Radiology Using Amorphous Selenium”, in Medical Imaging VI: Instrumentation, SPIE 1651, 134, (1992), and in L. E. Antonuk, J. Boudry, W. Huang , D. L. McShan, E. J. Morton, J. Yorkston, M. J. Longo and R. A. Street, “Demonstration of Megavoltage and Diagnostic X-ray Imaging with Hydrogenated Amorphous Silicon Arrays”, Med. Phys. 19, 1455 (1992).
One disadvantage of prior art active matrix readout arrays is that each pixel is connected to a source line and a gate line of the associated switching transistor (e.g. thin film transistor (TFT)). This effectively reduces the fill factor for each pixel, unless an additional insulating layer is placed between the source lines or gate lines and the pixel electrodes.
Another disadvantage of prior art active matrix readout arrays is that it can be difficult and occasionally impossible to bond the arrays to external chips, when the gate our source line pitch is very small. Bonding technology is the main limiting factor in certain applications like mammography, where a pixel pitch as small as 50 microns is required. In mammography it is not possible to reduce the problem by bonding chips to every second line on both sides, since the active area on at least one side should be as close as possible to the chest wall and should not be bonded.
A further disadvantage of prior art active matrix readout arrays is that the charge amplifier design for such prior art arrays usually suffers from a trade-off between sensitivity and dynamic range. In particular, where a charge amplifier has been designed for high sensitivity in a prior art active matrix read-out array, such an amplifier is not capable of measuring large signals due to saturation of the response.
SUMMARY OF THE INVENTION
According to the present invention, circuitry is provided which, in one application, is capable of reducing by half the number of source lines or gate lines in an active matrix read-out array, and which, in another application, maintains the usual number of source lines and gate lines, but is capable of extending the dynamic range of the charge amplifiers. By reducing the number of source lines and gate lines, the circuitry of the present invention enjoys substantially increased fill factor on a per-pixel basis than prior art designs. The circuitry of this invention also increases the pitch of the gate or data lines, so that fewer channels are required in the peripheral gate drivers or charge amplifiers and fewer wire bonds to these external devices are needed. This results in lower cost and improved reliability and the ability to provide higher resolution within a given bond pitch constraint. On the other hand, when the circuitry of the present invention is operated using the usual number of source and gate lines, extended dynamic range is provided over the prior art while maintaining high sensitivity of the charge amplifiers.


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A large area solid-state detector for radiology using amorphous selenium Medical Physics Research, Sunnybrook Health Science Centre, Toronto, Canada.
Demonstration of megavoltage and diagnostic x-ray imaging with hydrogenated amorphous silicon arrays Med. Phys. 19 (6) Nov./Dec. 1992.

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