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

摘要

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/sub M/, and enhance the maximum-gain quality factor Q/sub 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/sub 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/sub M/ near 185 MHz and the maximum-gain quality factor Q/sub 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.