Fast Multi Harmonic Active Load-Pull
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2012
A fast multi harmonic active load-pull setup is presented in this paper. The heart of the system is a large signal
network analyzer (LSNA, Maury/NMDG MT4463). The LSNA measures the voltage and current time domain
waveforms at the device terminals. The load reflection coefficient (ΓL(f)) is realized by injecting an amplitude and
phase controlled signal at the wanted harmonic on the output of the transistor, according to:
ΓL(f) = a2(f0)b2(f0)=A(VI, VQ)ej(ω0+θ(VI,VQ))b2(f0)(1)
The speed of the system is significantly improved by using the LSNA in modulation mode. This allows for
multiple impedance states to be presented during the measurement time of the LSNA. More than 180 impedance
states can be measured within 21 ms. The sample clock of the LSNA and the vector modulators, controlling the
load impedance, needs to be synchronized. A digital pattern generator (DPG) is therefore used in the setup to
enable the synchronization, and also to trigger the start of the measurement. Furthermore, a new optimization
algorithm is implemented to reduce the number of iterations needed to realize the desired load impedance. The
optimization is based on the Newton-Raphson algorithm, and convergence is obtained within 3-5 iterations for one
harmonic. The optimization is carried out simultaneously for all wanted harmonics, and multiple impedance states.
This significantly reduce the total measurement time for multi harmonic load-pull measurements.