Time Mismatch Effect in Linearity of Hybrid Envelope Tracking Power Amplifier

In this letter, a linearity degradation according to the time mismatching between RF and envelope paths in the hybrid envelope tracking (ET) power amplifier (PA) has been mathematically analyzed. From analysis, an asymmetric IM3 level of ET PA can be found due to the time mismatching between RF and envelope paths and AM-to-PM distortion of PA. For the experimental demonstration, the hybrid ET PA was designed for a wideband code division multiple access downlink band operating at a center frequency of 2.14 GHz. For the accurate time matching, the group delay time adjustor (GDTA) with 5 ns variation was employed in front of the RF PA. In the experiment, 4.78 dB improvement of ACPR for 4-FAs (frequency allocations) WCMDA signal of 20 MHz channel bandwidth was obtained by the optimum group delay tuning of the GDTA.