The design of CMOS continuous-time VHF current and voltage-mode lowpass filters with Q-enhancement circuits

Abstract

In this paper, very high frequency (VHF) current and voltage biquadratic lowpass filters implemented directly by the linear wideband finite-gain current and voltage amplifiers, respectively, are proposed and analyzed. A new Q-enhancement circuit which consists of a finite-gain wideband tunable voltage amplifier and a Miller capacitor is also proposed. It can increase the maximum-gain frequency f(M) and enhance the maximum-gain quality factor Q(M) of the VHF lowpass filters. Experimental results have successfully verified the capability of the proposed new filter implementation method in realizing both VHF current and voltage lowpass filters with maximum-gain frequency f(M) tunable in the range of 148 MHz to 92 MHz. It is also shown from experimental results that the VHF current lowpass biquad with the Q-enhancement circuit has the maximum-gain frequency f(M) near 185 MHz and the maximum-gain quality factor Q(M) up to 18.5. A fourth-order Chebyshev current lowpass filter with the cut-off frequency of 190 MHz has been successfully designed by using the current biquads with Q-enhancement circuits.