A 20MHz Low Dropout Controlled Current Sensor for Constant On-Time Based Envelop Tacking Supply Modulator for Radio Frequency Power Amplifier

This paper presents a LDO-controlled current sensor for accelerating constant on-time (COT) switching regulators (SWRs) for high efficiency envelope tracking power modulators (ETSMs) for RF power amplifiers (RF PAs). The proposed LDO-controlled current sensor controls the feedback loop of the SWR, rather than the traditional current sensing technique, in the case of fast envelope tracking. The LDO regulator behaves as the master to rapidly trigger the SWR as a slave energy provider to rapidly deliver the average energy to the RF PA for high efficiency. The experimental results show that the test chip fabricated in 0.18μm CMOS process can accurately track the RF envelope signal, and the peak efficiency is 86.7% when the power is 0.95W.