A COMPARISON OF 2 SWITCHED-CURRENT DIFFERENTIATORS AT EXTREMELY LOW CURRENT LEVEL

We are presenting comparative studies on two switched current (SI) dif ferentiators; one is a classical version, the other is a cumulative ve rsion. Both are applied to smart pixel time-domain differentiation. In both differentiators, the differentiation is calculated by subtractin g the instantaneous photocurrent from a previously sampled one, The ke y issue in this case is to obtain accuracy even with an extremely low current level (from pA to nA). The operability of both SI memories is verified through chip tests. Within an optical input dynamic range of five decades and a minimum level of 2 Lux (1pA in current), the maximu m current reproduction error rate is 10% for the first one and 6% for the second. Furthermore, the cumulability of the second version is als o confirmed by our tests.