A 1.3-V 5-mW fully integrated tunable bandpass filter at 2.1 GHz in 0.35-μm CMOS

A 2.1-GHz 1.3-V 5-mW fully integrated Q-enhancement LC bandpass biquad programmable in f_o, Q, and peak gain is implemented in 0.35-μm standard CMOS technology. The filter uses a resonator built with spiral inductors and inversion-mode pMOS capacitors that provide frequency tuning. The Q tuning is through an adjustable negative-conductance generator, whereas the peak gain is tuned through an input G_m stage. Noise and nonlinearity analyses presented demonstrate the design tradeoffs involved. Measured frequency tuning range around 2.1 GHz is 13%. Spiral inductors with Q_o of 2 at 2.1 GHz limit the spurious-free dynamic range (SFDR) at 31-34 dB within the frequency tuning range. Measurements show that the peak gain can be tuned within a range of around two octaves. The filter sinks 4 mA from a 1.3-V supply providing a Q of 40 at 2.19 GHz with a 1-dB compression point dynamic range of 35 dB. The circuit operates with supply voltages ranging from 1.2 to 3 V. The silicon area is 0.1 mm².