A 5.5-GHz Background-Calibrated Subsampling Polar Transmitter With-41.3-dB EVM at 1024 QAM in 28-nm CMOS

A 5.5-GHz Background-Calibrated Subsampling Polar Transmitter With-41.3-dB EVM at 1024 QAM in 28-nm CMOS ■

Nereo Markulic, Nereo Markulic, Nereo Markulic, Pratap Renukaswamy, Pratap Renukaswamy, Pratap Renukaswamy, Ewout Martens, Ewout Martens, Ewout Martens, Barend Van Liempd, Barend Van Liempd, Barend Van Liempd, Piet Wambacq, Piet Wambacq, Piet Wambacq, Jan Craninckx, Jan Craninckx, Jan Craninckx

Abstract ■

We present a subsampling polar transmitter (SSPTX) in 28-nm CMOS that consists of a low-noise phase modulating (PM) digital subsampling phase-locked loop (PLL) and a harmonic rejection mixed (HRM) inverse-class-D (D -1 ) digital power amplifier (DPA) for amplitude modulation (AM). The DPA is, unlike in a typical polar transmitter (TX), placed within the PLL and the phase-error detection happens directly at the DPA output. The subsampling polar TX thus becomes sensitive not only to phase errors but also to modulation amplitude. That feature enables AM-AM and PM-PM distortion to be detected and cancelled digitally in the background, while the transmitter operates normally. Moreover, the AM-PM cross distortion is filtered by the loop itself. The chip operates from a 0.9-V supply at 5.5 GHz with 2.5 MHz BW (1024 QAM) with average 1.1-dBm output power and total power consumption of 50 mW.