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Noise Compensation for Charge Coupled Devices

IP.com Disclosure Number: IPCOM000079794D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Chai, HD: AUTHOR [+3]

Abstract

In the application of charge-coupled devices (CCD) as an optical scanner or a delay line with an analog, electrical input, there exist several noise sources which degrade the output signal. They are: (1) Background charge generation, (2) Output amplifier noise, (3) Capacitive noise due to clocking gates, (4) Reset noise, (5) Fast interface state trapping noise, and (6) Transfer noise.

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Noise Compensation for Charge Coupled Devices

In the application of charge-coupled devices (CCD) as an optical scanner or a delay line with an analog, electrical input, there exist several noise sources which degrade the output signal. They are: (1) Background charge generation,
(2) Output amplifier noise, (3) Capacitive noise due to clocking gates, (4) Reset noise, (5) Fast interface state trapping noise, and (6) Transfer noise.

The first four noises are either reduced or eliminated by use of the compensation CCD shown in the circuit.

In the fabrication, both the signal CCD and the compensation CCD are on the same chip with the same substrate and the same clock lines, separated by a stop diffusion to avoid signal charge spilling down to the compensation CCD from the signal CCD. Hence the background charge generation and the clocking noise should be the same. Also at the outputs of the CCD's, amplifiers and resetting elements are fabricated on the same chip resulting in the same noise level. Consequently, when the outputs of the CCD's are inputted to a differential amplifier, the noises will be effectively cancelled. The signal output from the differential amplifier will be free from the first four noise sources.

The fast interstate trapping noise is not eliminated by the compensation CCD. Its effect can be reduced by introducing a "fat zero" noise, such that the fast interstates are effectively filled by the "fat zero" noise. The transfer noise (due to signal lo...