A 2.4GHz, 20dBm class-D PA with single-bit digital polar modulation in 90nm CMOS

Polar transmitters are a promising alternative to traditional Cartesian architectures in terms of flexibility and power efficiency. Such systems are often difficult to implement due to wideband amplitude and phase signals and may require predistortion to meet EVM and spectral requirements. This work demonstrates a highly-linear digital-polar system implemented in 90 nm CMOS. The amplitude is controlled with pulse-density modulation of the RF carrier. Phase information is provided with the RF clock. The class-D PA achieves peak efficiency of 38.5% at 2.4 GHz, including power of the PA drivers and insertion loss of the bandpass filter. The system does not require predistortion, and achieves rms-EVM levels of 1.8-2.1% for pi/4DQPSK and 8DPSK test vectors. The spectral mask for Bluetooth 2.1+EDR is satisfied under normal operating conditions.