With continuing reference to FIG. 8, the MLS envelope tracker 902 receives the envelope signal from the reconstruction filter 925 and a battery voltage V_BATT from the battery 901, and uses the differential envelope signal ENV_p, ENV_n to generate a power amplifier supply voltage V_{CC_PA} for the power amplifier 903 that changes in relation to the envelope of the RF signal RF_IN. The power amplifier 903 receives the RF signal RF_IN from the I/Q modulator 910, and provides an amplified RF signal RF_OUT to the antenna 906 through the duplexing and switching circuit 905, in this example.

The directional coupler 904 is positioned between the output of the power amplifier 903 and the input of the duplexing and switching circuit 905, thereby allowing a measurement of output power of the power amplifier 903 that does not include insertion loss of the duplexing and switching circuit 905. The sensed output signal from the directional coupler 904 is provided to the observation receiver 911, which can include mixers for providing down conversion to generate downconverted I and Q signals, and DACs for generating I and Q observation signals from the downconverted I and Q signals.