Integrated Synthetic Fourth-Order $Q$ -Enhanced Bandpass Filter With High Dynamic Range, Tunable Frequency, and Fractional Bandwidth Control

This paper demonstrates a tunable synthetic fourth-order bandpass filter (BPF) at microwave frequencies. Two parallel second-order Q-enhanced LC BPFs responses are added with the out of phase to synthesize a fourth-order BPF response. The filter is implemented in a 130-nm SiGe BiCMOS technology with a core die area of <inline-formula> <tex-math notation="LaTeX">$0.53 \times 0.7$ </tex-math></inline-formula> mm². The filter center frequency can be tuned from 4 to 8 GHz (C-band). The filter also achieves a wide 3-dB fractional bandwidth (BW) tuning range of 2%–25%, with a passband ripple of less than 0.5 dB. The corresponding normalized dynamic range (DR) is 151–166 <inline-formula> <tex-math notation="LaTeX">$\text {dB}\cdot \text {Hz}$ </tex-math></inline-formula> owing to a switched varactor control scheme to realize a large effective tuning range with high linearity. Using the parallel synthesis approach, the filter can maintain the DR of a second-order BPF while achieving a fourth-order frequency selectivity, which is favorable compared to cascading resonators. On the lower side of the band, the filter achieves more than 65 dB of ultimate rejection. On the upper side, the rejection is more than 52 dB. The filter also employs a variable transconductor for noise-linearity tradeoff flexibility. The power consumption of the filter is 112–125 mW over the above fractional BW tuning range at the target C-band.