CMOS CONTINUOUS-TIME CURRENT-MODE FILTERS FOR HIGH-FREQUENCY APPLICATIONS

Design considerations for high-frequency CMOS continuous-time current-mode filters are presented in this paper. The basic building block is a differential current integrator with its gain constant set hy a small-signal transconductance and a gate capacitance. A prototype fifth-order low-pass ladder filter implemented in a standard digital 2-mum n-well CMOS process achieved a -3-dB cutoff frequency (f0) of 42 MHz; f0 was tunable from 24 to 42 MHz by varying a reference bias current from 50 to 150 muA. Using a single 5-V power supply with a nominal reference current of 100 muA, the five-pole filter dissipated 25.5 mW. The active filter area was 0.056 mm2/pole. With the minimum input signal defined as the input-referred noise integrated over a 40-MHz bandwidth, and the maximum input signal defined at the 1% total intermodulation distortion (TIMD) level, the measured dynamic range was 69 dB. A third-order elliptic low-pass ladder filter was also integrated in the 2-mum n-well CMOS process to verify the implementation of finite transmission zeros.