Parasitic-insensitive switched-capacitor variable all-pass filters that have small total capacitance

This paper proposes a method of constructing first- and second-order switch ed-capacitor variable all-pass circuits that have small total capacitance a nd are parasitic-insensitive. A first-order circuit, in which the peak grou p delay at zero angular frequency can be specified by using a programmable capacitor array, and a second-order circuit that has a first-order subcircu it, in which the peak bandpass group delay and the corresponding angular fr equency (peak angular frequency) can be specified independently, have alrea dy been presented. Those constructions, however, have the problem that the capacitance spread is generally enlarged in the first-order circuit (define d here as the maximum capacitance when the minimum capacitance is normalize d to 1). This increases the total capacitance in both the first- and second -order circuits and makes the second-order circuit parasitic-sensitive. Thi s paper, on the other hand, proposed circuits that are parasitic-insensitiv e and have smaller total capacitances than the circuits proposed in the pas t. The second-order circuit proposed in the past also has the problem that the peak angular frequency cannot be set higher than half the Nyquist angul ar frequency, but this is possible in the proposed second-order circuit. An other point is that the number of operational amplifiers is reduced by one in the proposed circuit. The calculated amplitude element-sensitivities of the first- and second-order circuits are smaller than the past values. The proposed circuit was experimentally constructed using discrete components, and a satisfactory result was obtained. (C) 1999 Scripta Technica.