A SAW-Less 3FLO-Suppression RF Transmitter with a Transformer-Based N-Path Switched-Capacitor Modulator Achieving -157.6dBc/Hz Output Noise and -61dBc CIM₃

This paper reports a SAW-less RF transmitter with a passive-intensive I/Q modulator. Specifically, without the noisy and nonlinear transconductor (gm), our proposed linear I/Q modulator features a transformer-based N-path switched-capacitor (SC) topology to enable high-Q bandpass filtering at a flexible RF, rejecting the out-of-band (OB) noises in baseband (BB) and the modulator. The intrinsic lowpass characteristic of the transformer also reduces the harmonic terms at 3×fLO at the output of the modulator, thereby effectively suppressing CIM₃. For the power amplifier (PA) driver, it is aided by a paralleled-gm linearizer to improve the performance. Prototyped in a 65nm CMOS process, our transmitter manifests a consistently low OB noise (≤-157dBc/Hz) for 2 to 3GHz. Under a 2.3dBm output power, the transmitter shows a high transmitter efficiency (5.1%) and a high linearity (CIM3 <-60dBc and ACLR1 <-46dBc). The power consumption is 32.5mW at 2.5GHz, and the active area is 0.21mm².