Bias circuit design of RF power amplifiers for TDD systems

In Time Division Duplex(TDD) system, the radio frequency (RF) power amplifier in a repeater is turned on only when it receives RF signal, thus implementing the sub-frame synchronization and the second conversion point of timeslots is important in TDD system. This paper introduce a bias circuit design to realize the control of the RF power amplifier in the down-link through envelop detection of the received RF signal. The experimental results demonstrated that the proposed bias circuit can properly control the operation status of the power amplifier for a TD-SCDMA system.