THE DESIGN OF CMOS CONTINUOUS-TIME VHF CURRENT AND VOLTAGE-MODE LOWPASS FILTERS WITH Q-ENHANCEMENT CIRCUITS

In this paper, very high frequency (VHF) current and voltage biquadrat ic lowpass filters implemented directly by the linear wideband finite- gain current and voltage amplifiers, respectively, are proposed and an alyzed. A new Q-enhancement circuit which consists of a finite-gain wi deband tunable voltage amplifier and a Miller capacitor is also propos ed. It can increase the maximum-gain frequency f(M) and enhance the ma ximum-gain quality factor Q(M) of the VHF lowpass filters. Experimenta l results have successfully verified the capability of the proposed ne w filter implementation method in realizing both VHF current and volta ge lowpass filters with maximum-gain frequency f(M) tunable in the ran ge of 148 MHz to 92 MHz. It is also shown from experimental results th at the VHF current lowpass biquad with the Q-enhancement circuit has t he maximum-gain frequency f(M) near 185 MHz and the maximum-gain quali ty factor Q(M) up to 18.5. A fourth-order Chebyshev current lowpass fi lter with the cut-off frequency of 190 MHz has been successfully desig ned by using the current biquads with Q-enhancement circuits.