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This article reports a multiband frequency-division duplex (FDD) SAW-less transmitter (TX) for 5G new radio (5G-NR). It features a bandwidth-extended $N$ -path filter-modulator (BW-Ext FIL-MOD) to enable high- $Q$ bandpass filtering at a flexible RF and the synthesis of a complex-pole pair via merging positive- and negative-feedback networks (PFN/NFN) enhances its bandpass characteristic, surmounting the tradeoff between the passband flatness and out-of-band (OB) rejection, a switched-baseband (BB) input network to avoid the mutual loading effect between the BW-Ext FIL-MOD and itself, and a transimpedance amplifier (TIA)-based power-amplifier driver (PAD) to absorb both the bias and signal currents of the BW-Ext FIL-MOD for better linearity and power efficiency. Fabricated in 28-nm CMOS, the proposed TX manifests a 20-MHz passband BW and a consistently low OB noise (≤−157.5 dBc/Hz) for different 5G-NR bands between 1.4 and 2.7 GHz. The TX achieves sufficient output power (3 dBm), high TX efficiency (2.8%–3.6%), and high linearity (ACLR1 < 44 dBc and EVM < 2%). The active area is 0.31 mm2.

This paper describes a wideband ultra-fast-settling fractional-N bang-bang digital phase-locked loop (DPLL) for multi-ISM-band ultra-low-power (ULP) radios. We propose a mismatch-free digital-to-time-converter (DTC) gain calibration scheme to effectively shorten the calibration time, while the split coarse-fine PLL loops with different loop bandwidths accelerate the loop settling speed. The employed ring VCO (RVCO) aids to extend the frequency tuning range and generate multi-phase outputs. Prototyped in 65-nm CMOS, the DPLL consumes 1.2–2.4 mW over a wide frequency locking range of 68.3% (1.3–2.65 GHz) and occupies a die area of 0.12 mm2. The settling time measures $8~\mu \text{s}$ at an 82-MHz initial frequency error.

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.

This paper proposes a surface-acoustic wave (SAW)-less tunable RF front end (RF-FE) using an electrical-balance duplexer (EBD) integrated with a switched-LC N-path low-noise amplifier (LNA). The EBD cancels the transmitter–receiver (TX–RX) leakage at the RX frequency by dynamically optimizing the balance of a hybrid transformer, which enables in-band full-duplex (IBFD) operation. A transconductor-based LNA in parallel with a switched-LC N-path network creates input and output notches to reject TX leakage for frequency-division duplexing (FDD) operation. The LNA’s signal-handling capability is enhanced via optimum switch biasing. Fabricated in 0.18- $\mu \text{m}$ SOI CMOS, the RF-FE offers >50-dB tunable rejection from the TX port to LNA output at both TX and RX frequencies, for all 3GPP bands from 0.7 to 1 GHz (i.e., FDD case). It is the first tunable RF-FE including an LNA that achieves +70-dBm TX-path IIP3, and +30-dBm in-band TX power while cancelling the self-interference by >50 dB (i.e., IBFD case). The RF-FE consumes 62.5 mW at 1 GHz with 11.7-dB RX cascaded NF, 3.6-dB TX insertion loss, and 9.62 mm2 active area.

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.

This paper proposes a self-interference-resilient LNA for the FDD-LTE covering 0.7 to 1GHz. It incorporates a switched-LC N-path network with gain-boosting and optimum-biasing techniques to enhance the out-of-band (OOB) linearity at ≥40MHz offset. Implemented in 0.18µm SOI CMOS, the LNA achieves >31.2dB output rejection, +26.2dBm (+8dBm) OOB-IIP3 (iB 1dB ) at ≥40MHz offset and 6.8dB blocker NF at +4dBm blocker power for the default mode, while consuming a reasonable power of 48.4 to 62.5mW. When reconfigured to high-rejection mode, the LNA offers a tunable cancellation notch improving the output rejection to >50dBc.