The continuous-time VHF lowpass filter design using finite-gain current and voltage amplifiers and special Q-enhancement circuit

A linear wideband class AB finite-gain current amplifier is proposed and analyzed. Considering the intrinsic capacitance of the MOS transistors as filter elements, the current amplifier can be viewed as a VHF lowpass biquad filter. The center frequency fo is tunable from 79.4 MHz to 144.5 MHz and the quality factor Q is tunable from 1.03 to 1.19. A linear wideband class AB finite-gain voltage amplifier is also proposed and analyzed. Similarly, the unity-gain voltage amplifier can also be regarded as a VHF voltage biquad lowpass filter with the center frequency tunable from 81 MHz to 134.89 MHz and the quality factor tunable from 1.12 to 1.59. A new and special Q-enhancement circuit is also proposed to increase the center frequency fo and enhance the quality factor Q of the VHF filters. It is shown that the center frequency fo is tunable from 173.78 MHz to 205.6 MHz and the quality factor Q tunable from 1.69 to 7.21