A 28 GHz Phased-Array Transmitter Based on Doherty Spatial Combining Technique With a Local Sub-Sampling PLL

This paper presents a 28 GHz integrated phased-array transmitter, utilizing an over-the-air (OTA) combining technique for power efficiency boosting and a local oscillator (LO) phase shifting. Efficiency boosting is achieved by decomposing the baseband signal into two streams, one with a reduced peak-to-average power ratio (PAPR) and the other consisting of the low-occurrence peak residuals. Compared to uniformly excited linear phased array (UELA), the efficiency improvement is by 40%. The two streams are up-converted and transmitted through the radio-frequency (RF) chains, each optimized for the corresponding output power, and recombined OTA to reconstruct the original signal. Each chain contains a power-optimized sub-sampling phase-locked loop (SSPLL) that accounts for the phase shift and achieves a better than 1° phase resolution. We implemented the four TX chains on a standard 65 nm bulk-CMOS process, achieving a system efficiency of 7.6% at 21 dBm equivalent isotropic radiated power (EIRP), with an error vector magnitude (EVM) of -31 dB.