A MOSFET-only continuous-time bandpass filter

A MOSFET-only filter is described which employs an amplifier-regulated cascode structure to realize both conductance and transconductance, while the required capacitors are realized by MOSFET gate capacitance. Distortion due to mobility degradation and MOSFET capacitor nonlinearity is analyzed, as is the effect of finite gain-bandwidth product of the regulating amplifiers on the filter's linearity and high frequency performance. A prototype second-order bandpass filter has a center frequency of 560 kHz, a third-order intermodulation of -41 dB for 0 dBm input and a dynamic range of 60 dB. It consumes 2.5 mW from a 5 V supply and occupies 0.18 mm/sup 2/ in a 1-/spl mu/m digital CMOS technology.