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 (g
m
), 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 3xf
LO
at the output of the modulator, thereby effectively suppressing CIM
3
. For the power amplifier (PA) driver, it is aided by a paralleled-g
m
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 (CIM
3
<-60dBc and ACLR
1
<-46dBc). The power consumption is 32.5mW at 2.5GHz, and the active area is 0.21mm
²
.