A 900MHz GFSK and 16-FSK TX Achieving Up to 63.9% TX Efficiency and 76.2% PA Efficiency via a DC-DC-Powered Class-D VCO and a Class-E PA

This brief presents a highly efficient transmitter capable of radiating GFSK and 16-FSK modulated signals in the 900MHz ISM band. Multiple low power techniques are exploited such as a class-D VCO and a class-E single stage PA to enhance the TX efficiency. Using an on-chip DC-DC converter, the VCO can operate with down to a 250mV supply and generate 750mV signals to the input of the PA. A phased locked loop (PLL) is implemented for rapid calibration of the LO frequency and is locked to a 2MHz crystal, which also provides the clock for the DC-DC converter. The fabricated integrated circuit occupies 1mm² area in 65nm LP CMOS, achieves a peak 76.2% PA efficiency and 63.9% TX efficiency, while being capable of delivering up to 3dBm to a $50\Omega $ antenna.