High-Performance SAW-Less TDD/FDD RF Front-Ends

In order to develop multiband cellular radios at low cost, the rekindled on-chip N-path switched-capacitor filter is a promising replacement of the off-chip SAW (surface acoustic wave) filters, due to its property of high-Q filtering over a wide RF (radiofrequency) range. This chapter discusses the design of two SAW-less RF front-ends for TDD (time-division duplexing) and FDD (frequency division duplexing). The first is an area-efficient SAW-less wireless transceiver for multiband TDD that utilizes an N-path switched-capacitor gain loop. Fabricated in 65-nm CMOS, the transmitter mode reaches a −1-dBm output power with a −40-dBc ACLREUTRA1 at 1.88 GHz and a −154.5-dBc/Hz OB noise at 80-MHz offset; the receiver mode reaches 3.2-dB NF and +8-dBm OB-IIP3. The second is a fully integrated multiband FDD SAW-less transmitter for 5G-NR in 28-nm CMOS. It features a bandwidth-extended N-path filter modulator to enable both wide bandwidth and high-Q bandpass filtering, also including an isolated baseband (BB) input network and a transimpedance amplifier-based power amplifier driver. The transmitter manifests a 20-MHz passband bandwidth and a low OB noise (≤ −157.5 dBc/Hz) between 1.4 and 2.7 GHz. Under 3-dBm output power, it exhibits high efficiency (2.8–3.6%) and linearity (ACLR1 <44 dBc and EVM <2%). This chapter presents both designs in detail.