A 2.5 GHz monolithic silicon image reject filter

A low power 2.5 GHz monolithic silicon bipolar image rejection filter for superheterodyne receiver application is presented; which uses an on-chip inductor and a negative resistance circuit to realize a notch filter with better than 50 dB rejection (measured) at the image frequency. Using 0.8 micron BiCMOS technology a tuned amplifier was fabricated with 1.9 GHz passband, a deep notch at 2.5 GHz to attenuate the image frequency (assuming 300 MHz intermediate frequency (IF)), and 3.2 mA current consumption at +3 V. A second chip incorporated a varactor to add notch frequency tuning capability over a 239 MHz range.