A 0.75–2.5-GHz All-Digital RF Transmitter With Integrated Class-E Power Amplifier for Spectrum Sharing Applications in 5G Radios

We propose a digitally intensive, reconfigurable RF transmitter with an integrated, tunable Class-E power amplifier (PA) which can be configured to operate from 0.75 to 2.5 GHz in discrete bands, while delivering an output power of 11.5 dBm up to 1.5 GHz and 6.5 dBm up to 2.5 GHz. Digital signal processing is exploited to suppress sampling spurs up to the harmonics of the carrier, thus eliminating the need for sharp RF filters. The proposed techniques make the transmitter adaptable to signals of different bandwidths and to different carrier frequencies with minimal overhead in power and area when compared to other digital transmitter designs. Digital predistortion is used to linearize the PA. The transmitter also includes clock correction circuitry for correcting duty cycle and quadrature errors. A generic design methodology is mathematically developed for a reconfigurable Class-E PA with a fixed series inductor. This transmitter scales well with technology and can be potentially used for spectrum sharing (SS) applications in fifth generation (5G) radios. Implemented in a 130-nm CMOS technology, the proposed transmitter occupies an area of 1 mm
²
. A maximum output power of 13.7 dBm with a maximum efficiency of 27% is obtained at 1 GHz.