10.1 A 1.4-to-2.7GHz FDD SAW-Less Transmitter for 5G-NR Using a BW-Extended N-Path Filter-Modulator, an Isolated-BB Input and a Wideband TIA-Based PA Driver Achieving <−157.5dBc/Hz OB Noise

For the sub-6GHz 5G New Radio (5G-NR), most FDD bands expand their signal bandwidth (BW) to 20MHz. In the NR-n74 Band (~1.45GHz), the duplex spacing (Δf) is only 48MHz. Such a small Δf/BW ratio (2.4) challenges the design of a multiband FDD SAW-less transmitter (TX) that must emit negligible noise at the nearby receiver (RX) band. Previous works [1], [2] use high-order baseband (BB) filters, along with large bias currents, to suppress the out-of-band (OB) noise, but the power (>90mW) and area (−1mm2) are large for an OB noise of −158dBc/Hz [2]. Although the charge-domain direct-launch digital TX [3] is more flexible and area-efficient (0.22mm2), it entails off-chip baluns to extend the RF coverage, and has a limited output power (-3.5dBm). An alternative is to embed a gain-boosted N-path filter into the TX [4], such that high-Q bandpass filtering can be performed at a flexible RF. Still, the filtering effectiveness of [4] is moderate when the signal BW reaches 10MHz, showing an OB noise of just −154.5dBc/Hz.