A 250-MHz gm-C filter with discrete tuning scheme in 0.18-μm CMOS for UWB receiver

A low noise, 250-MHz fifth order 0.1 dB ripple Chebyshev g_m-C filter, with a novel discrete tuning scheme is presented. The discrete tuning circuit switches ON/OFF small g_m cells which are connected in parallel to the main g_m cell, based on the PVT conditions, to correct for the shift in the cutoff frequency f_c. Compared to conventional tuning schemes, proposed discrete scheme demonstrates improved performance in terms of noise and optimal voltage swing across PVT. The chip was fabricated in standard 0.18-μm CMOS technology. Measured results show a f_c of 245 MHz, equivalent input noise voltage of 166 μV, IIP3 of -2.5 dBV in pass band and 2.5 dBV in stop band, Input referred P1dB of -6.6 dBV, IIP2 of 55 dBV, consuming 19 mA from 1.8 V supply. The tuning circuit, in combination with a PTAT bias, maintains the bandwidth within ±5% of nominal f_c of 250 MHz for VDD variation of 1.8±0.1V and temperature variation of -40°C to 85°C.