| 摘要 |
If the envelope-tracking supply lags behind the corresponding RF input to the power amplifier the instantaneous PA gain and output amplitude are higher when the envelope is falling than when it is rising (figure 2). Conversely, if the envelope-tracking supply leads the corresponding RF input the gain and amplitude are lower when the envelope is falling than when it is rising (figure 1). A variable delay 16 may thus be adjusted to achieve time alignment of the envelope and RF signals by comparing 50 the amplifier gain or output amplitude measured when the envelope is rising against the amplifier gain or amplitude measured when the envelope is falling. The slope of the envelope signal is derived by a differentiator 42, the squared output of which gates gain values 68 or amplitude values (34, figures 4 and 5) to respective running average filters 46,48. Alternatively, the measured positive-slope or negative-slope gain may be compared with the average gain or amplitude. The delay control system tracks temperature changes. No factory calibration of delay is required. |
