Pascal and Chebyshev approximations are used in passive filter design and have similar design limitations when the order turns out to be even. These design issues are thoroughly addressed, and the exact conditions are set under which passive even-order Chebyshev and Pascal filters cannot be directly synthesised and either the order has to be increased to the next odd integer value or the modified filter must be designed. It is shown that the even-order design issue is much less restricting in the Pascal case, making Pascal superior to Chebyshev filters in that even order filters can be directly designed to meet specifications that cannot be met by Chebyshev filters of the same even order.

This paper analyzes the impact of parasitic capacitances in the performance of split capacitive-based digital-to-analog converter arrays and presents a procedure for the optimal sizing of these structures for given linearity specifications. It also demonstrates that parasitics are often the main responsible for the nonlinear behavior of these arrays, particularly for low-to-medium resolution converters. In order to validate the analysis, two versions of a complete low-power, low-voltage successive-approximation register analog-to-digital converter (ADC), intended for a disposable multi-channel bio-medical monitoring system, have been fabricated in a 0.35µm standard complementary metal-oxide-semiconductor technology. The only difference between these two prototypes is that in one of them, the capacitive array is surrounded by dummy capacitors, while in the other prototype is not. Hence, the former achieves better mismatch performance at the expense of increased parasitics. The experimental results demonstrate that the version without dummy capacitors obtains higher effective resolution than the ADC with dummies, the power consumption being essentially the same for both prototypes, namely: 130nW at 2kS/s from a 1-V supply. These results are in full agreement with the analysis reported in the paper and confirm the proposed sizing procedure.