A 0.038-mm2 SAW-Less Multiband Transceiver Using an N-Path SC Gain Loop

Abstract

An N-path switched-capacitor (SC) gain loop is proposed as an area-efficient surface acoustic wave-less wireless transceiver (TXR) for multiband TDD communications. Unlike the direct-conversion transmitter (TX: baseband (BB) filter $\to$ I/Q modulation $\to$ PA driver) and receiver (RX: LNA $\to$ I/Q demodulation $\to$ BB Filter) that the functions are arranged in an open-loop style, here the signal amplification, bandpass filtering, and I/Q (de)modulation are unified in a closed-loop formation, being reconfigurable as a TX or RX with a local oscillator (LO)-defined center frequency. The key advantages are the multiband operation capability in the TX mode, and high resilience to out-of-band (OB) blockers in the RX mode. Fabricated in a 65-nm CMOS, the TXR prototype consumes up to 38.4 mW (20 mW) in the TX (RX) mode at the 1.88-GHz long-term evolution (LTE)-band2. The LO-defined center frequency covers >80% of the TDD-LTE bands with neither on-chip inductors nor external input-matching components. By properly injecting (extracting) the signals into (from) the N-path SC gain loop, the TX mode achieves an −1 dBm output power, a −40 dBc ACLREUTRA1, and a 2% EVM at 1.88 GHz, while showing a −154.5 dBc/Hz OB noise at 80-MHz offset. In the RX mode, a 3.2-dB noise figure and a +8 dBm OB-IIP3 are measured. The active area (0.03 mm2) of the TXR is 24 $\times$ smaller than the state-of-the-art LTE solutions.