Application of reverse-active npns for compact, wide-tuning fT-integration-based filters in SiGe HBT BiCMOS technology

The f_T-integration principle is investigated in SiGe HBT 0.8 μm BiCMOS process through an implementation of wide frequency tuning 5-GHz biquadratic filters. The techniques formerly employed in Si f_T-integrators, including the circuit structures and the use of lateral pnp as well as vertical npn operating in a reverse-active mode for wide tuning, are successfully demonstrated in a SiGe HBT process. The prototype filters achieves a center frequency tuning from 1.9 GHz to 6.7 GHz (over 300%) and SFDR of 30 dB and 33 dB for the corresponding Q of 10 and 5 respectively at a 1.8-V supply. The vertical reverse-active tuning npn structures help save chip area by four times over the use of lateral pnp structures, while overall performance is still preserved.