A BiCMOS programmable continuous-time filter using image-parameter method synthesis and voltage-companding technique

This paper presents a BiCMOS realization of a structure-programmable continuous-time filter built with sections synthesized by the image-parameter method and demonstrating the feasibility of the voltage companding technique. The circuit implements any one of four lowpass filters of order 2-5 or one fourth-order bandpass filter by interconnecting a set of identical cells. The filter is obtained by a component level substitution transforming a g_m -C structure into its log-domain equivalent. The g_m-C structures are derived from LC ladder prototypes which are synthesized using the image-parameter method. This technique can be extended to realize higher order filters using multichip configurations. As an example, six lowpass filters (order 6-11) and three bandpass filters (order 6, 8, and 10) have been measured using three chips. The programmable filters can additionally be frequency tuned from 10-100 kHz with a low total harmonic distortion (THD) despite their class AB operation