Tuning methods for digital hybrid load pull system
View Patent ↗A digital high-speed hybrid load pull test system comprises a slide screw automatic passive tuner, a digital active forward injection loop in a closed loop transmission configuration, calibration and tuning algorithms. The forward active injection loop comprises at least one adjustable coupler, a digital electronic tuner and feedback power amplifier; the passive tuner comprises one or more metallic tuning probes, used to create passive reflection factors. Small signal calibration of the passive and active tuners create a global calibration data base, used to pre-tune in the area of the target impedance and final high power (nonlinear) tuning employs a in-situ signal power wave search and measurement for digital impedances around the small signal pattern. The system provides for high speed low injected power tuning with maximum reflection factor at DUT reference plane reaching unity.
1. A small signal pre-tuning procedure performed for a calibrated digital hybrid load pull tuner,
wherein
the digital hybrid load pull tuner includes
a passive tuning section controlled by settings XT and YT,
wherein
XT and YT are physical positions of a tuning probe of a slide screw tuner;
and
a digital active loop feedback section controlled by settings XC, YC and D;
wherein
XC and YC are amplitude and phase controls of a loop coupler and D is a setting of a digital tuner;
and
passive s-parameter calibration data [S1(XT,YT)] for the passive tuning section;
and
active s-parameter calibration data [S2(XC,YC,D)] for the digital active feedback loop;
comprising:
a) define a target reflection factor GAMMA.T=S11.T;
b) search in the passive calibration s-parameter data for the closest calibration point to the target reflection factor and save as S1.11(XT0, YT0);
c) search in the active calibration data for settings (XC0, YC0, D0) creating the smallest vector |S11.T−S1.11(XT0, YT0)−S2.11(XC, YC, D)|, and save the overall coordinates {XT0, YT0, XC0, YC0, D0}.
2. An iterative in-situ large signal tuning method performed using the tuner of claim 1 comprising the following steps:
a) insert a bidirectional coupler between a DUT and a test port of the digital hybrid load pull tuner, said coupler being calibrated to the DUT reference plane,
b) set the coordinates to {XT0, YT0, D0, XC0, YC0},
c) measure injected and reflected signal waves <b2> and <a2> at the DUT yielding S11=<a2>/<b2>,
d) change the states of the digital loop tuner iteratively to reduce |S11.T−S11|,
e) terminate if no further improvement,
f) go to step c).