A Comparison of Two Switched Current Differentiators at Extremely Low Current Level

Authors:
Chunyan Wang;Francis Devos;Yang Ni
Affiliations:
Institut d’Electronique Fondamentale, Bat.220, Universit Paris Sud, 91405 Orsay Cedex France;Institut d’Electronique Fondamentale, Bat.220, Universit Paris Sud, 91405 Orsay Cedex France;Institut National des Telecommunications, 91011 Evry Cedex, France Email: chunyan@ief-paris-sud.fr
Venue:
Analog Integrated Circuits and Signal Processing
Year:
1998

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Abstract

We are presenting comparative studies on two switched current (SI)differentiators; one is a classical version, the other is a cumulativeversion. Both are applied to smart pixel time-domain differentiation. Inboth differentiators, the differentiation is calculated by subtracting theinstantaneous photocurrent from a previously sampled one. The key issue inthis case is to obtain accuracy even with an extremely low current level(from pA to nA). The operability of both SI memories is verified throughchip tests. Within an optical input dynamic range of five decades and aminimum level of 2 Lux (1pA in current), the maximum current reproductionerror rate is 10% for the first one and 6% for the second.Furthermore, the cumulability of the second version is also confirmed by ourtests.