A Low-Pass Sense and Control Circuit for Switching Amplifier in Wideband Hybrid Envelope Tracking Supply Modulator

A low-pass sense and control circuit for hybrid envelope tracking supply modulator (ETSM) with wideband envelope signal is presented. The second-order low-pass filtering (LPF) circuit controls the switching frequency fsw of the switching amplifier (SA). Although only low-frequency signal is sampled, the SA tracks the average output power at a reasonable speed and the reduced fsw improves the efficiency of the whole ETSM. It is more suitable for wideband envelope signals than traditional methods. This circuit is applied to wideband envelope signal especially to frequencies greater than 100MHz. In our design, a 150MHz envelope signal is used for test and an average switching frequency about 3.6 MHz is obtained. With the efficiency of 94%, the SA can track the average output power in a reasonable speed.