Digital-IF WCDMA handset transmitter IC in 0.25-μm SiGe BiCMOS

Implemented in a 0.25-μm SiGe BiCMOS process, a highly integrated low-power transmitter IC (TxIC) is developed for wideband code-division multiple-access handset applications. Based on a digital-IF heterodyne architecture, it eliminates the external IF surface acoustic wave filter by adopting a meticulous frequency plan and a special-purpose second-order-hold D/A conversion scheme. The TxIC features a low-power high-speed D/A converter designed to drive a dominantly capacitive load. For the upconversion mixer and the RF amplifier, adaptive biases are designed to minimize the quiescent power consumption and to provide current boost only when needed. The TxIC achieves <1% EVM. It consumes 180 mW (3-V supply) for the maximum output power of +5 dBm and reduces to 120 mW during power backoff.