A Widely Tunable Switched-Capacitor Balun Based on N-Path Filters

This letter introduces an inductor-less eight-path balanced-to-unbalanced (balun) bandpass filter that performs single-to-differential conversion by switching the bottom plate of the
$N$
-path filter capacitors between ground and the negative terminal of the differential output. Measurement results of a 0.32-mm2 65-nm CMOS chip demonstrate an insertion loss below 3 dB, power consumption below 12.2 mW, a tunable range of 0.1–1 GHz, a high-selectivity filtering performance with a bandwidth of ~30 MHz, and input impedance matching capability. The amplitude (phase) imbalance is less than 0.3 dB (±3°) over the tuning range. The measured in-band IIP3, IIP2, OP1dB, and simulated noise figure are +13.8 dBm, +38 dBm, −4 dBm, and 2.45 dB, respectively, at a center frequency of 500 MHz.