28.7 A Wideband Blocker-Tolerant Receiver with High-Q RF-Input Selectivity and <-80dBm LO Leakage

Abstract

High-Q selectivity at RF input is strongly desirable for wideband radio receivers (WB-RX) to combat strong interferences present in today's cellular mobile communications. Originally explored in the 1950's, the N-path filtering technique has been revisited in recent years to realize tunable high-Q selectivity at RF input [1,2]. From a generic perspective shown in Fig. 28.7.1, it can serve as a bandpass filter in shunt with the wideband RF LNA or as a mixer-first direct downconversion architecture. The N-path technique, however, mandates mixing switches to be directly connected to the RF port with their on-resistances required to be much smaller than 50Ω This leads to excessively large switches and thus strong LO leakage of >-67dBm [1,2] in clear infraction of the <;-76dBm spurious emission requirement for 3GPP2 radios [3]. This work describes a WB-RX architecture that realizes high-Q bandpass (BP) selectivity at RX input while suppressing LO leakage down to <;-80dBm. As will be described, unlike conventional N-path-based RXs, this RX avoids direct switch connection to the antenna interface, thereby breaking the fundamental trade-off between the RX input selectivity and the LO leakage.