7 June 2004 CMOS active pixel sensor achieving 90-dB dynamic range with column-level active reset
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A CMOS active pixel sensor array using column-level active reset has been fabricated and tested. Column-level active reset requires one additional transistor per pixel, bringing the total to 4, and a per-column op-amp. The added transistor per pixel controls the gate of the reset transistor. There are two important feedback mechanisms in active reset. The first is the amplification by the Miller effect of the effective capacitance on the photodiode during reset, hence reducing kT/C noise. The second is the control of the resetting current via modulation of the transconductance of the reset switch. The level of noise reduction is comparable to, or may exceed, what true correlated double sampling can achieve. Readout noise of 44 microvolts and a dynamic range of 90 dB (15 bits), rms, has been measured. Room temperature noise as low as 5.1 electrons, rms, referred back to the photodiode node, has been measured on small photodiode pixels (5.8 fF capacitance). This compares to 38.3 electrons when measured with a standard “hard” reset, for a factor of 7.6 improvement. Row and column fixed pattern noise were also improved by up to a factor of 21, going from 1% for both to 0.048% and 0.27%, respectively.
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Yandong Chen, Yandong Chen, Stuart Kleinfelder, Stuart Kleinfelder, } "CMOS active pixel sensor achieving 90-dB dynamic range with column-level active reset", Proc. SPIE 5301, Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications V, (7 June 2004); doi: 10.1117/12.527111; https://doi.org/10.1117/12.527111

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