High-efficiency reconfigurable RF transmitter for wireless sensor network applications

In this paper, a 90-nm CMOS 1.2-V ultra-low-power RF transmitter for wireless sensor networks is presented. A wideband topology guarantees continuous frequency coverage from 300 to 960 MHz, thus enabling easy reconfigurability through the most popular sub-GHz bands. At 300 MHz (960 MHz), the transmitter is able to deliver a 10.2-dBm (10.3-dBm) output power with 63% (46%) system efficiency. The proposed circuit features extensive use of dynamic current biasing for improved efficiency in back-off. Substantial power saving in excess of 80% are achieved compared to constant bias operation. Linear operation with variable-envelope input is also demonstrated, since the transmitter exhibits a 8.5-dBm output power, 37% efficiency, and −30-dBc adjacent channel power ratio with π/4-DQPSK 200-ksps input excitation.