A Watt-Class Digital Transmitter with a Voltage-Mode Class-S Power Amplifier and an Envelope Delta-Sigma Modulator for 450 MHz Band

A single-bit high efficiency watt-class digital transmitter for the 450 MHz band is presented, using a GaN voltage-mode class-S power amplifier and a CMOS envelope ΔΣ modulator. The transmitter achieves 1.1 W output power with 69% drain efficiency for a 400 MHz WCDMA uplink signal, thus meeting the 3GPP specifications for ACLR. A power control from 0.45 W to 1.8 W is achieved by changing the supply voltage of the power amplifier from 20 V to 40 V, keeping the drain efficiency beyond 58% without any degradation of ACLR.