A 5-80MHz CMOS Gm-C Low-Pass Filter with On-Chip Automatic Tuning

A fifth-order CMOS Gm-C Chebyshev low-pass filter with a tunable cutoff frequency of 5-80 MHz is presented. A phase-locked loop (PLL) frequency synthesizer control system automatically references the frequency response of the filter to an external fixed clock frequency. Spectre simulation results of the 1.8-V filter in a 0.18-μm CMOS process show that the cutoff frequency varies by less than 1 percent for a temperature range of -40-85 °C. The complete circuit features 45 dB dynamic range and consumes 12.2-43.5 mW.