Fast on-chip tuning circuit for active RC filters using the SAR scheme

This paper presents a fast tuning scheme for active-RC filters of monolithic implementation. Due to the significant variations of passive resistor and capacitor values, it should be necessary for the filter to be equipped with the on-chip tuning circuitry. In this paper, the successive approximation register (SAR) scheme is incorporated for a prompt compensation of RC variations. The tuning time can be proportional to the number of bits in the tuning resolution scheme. The propose tuning scheme is included in implementation of the 5th-order Chebyshev-II lowpass filter, where 5-bit is used to achieve less than 2.5% cutoff frequency error with respect to RC time constant variations of /spl plusmn/40%.