A monolithic CMOS 2368±30 MHz transformer based Q-enhanced series-C coupled resonator bandpass filter

A three-pole 0.1 dB ripple Chebyshev series-C coupled resonator bandpass filter with transformer-based Q-enhancement is presented. This Q-enhancement technique compensates resonator loss and produces a flat passband response with low insertion loss. The compensation scheme uses frequency-dependent negative resistance to compensate frequency-dependent inductor losses, avoiding passband distortion, which is a problem with cross-coupled negative resistance circuits. Fabricated in 0.18 mu m CMOS, the measured filter center frequency is 2368 MHz with a 60 MHz (3 dB) bandwidth, including probe pad and connecting trace parasitic losses. The filter draws 5.84 mA at 1.5 V, and the die area is 1.5 mm x 1.5 mm.