Why the current consumption varies with output impedance when using PA?

[passerby]

Why the current consumption varies with output impedance when
using collector-voltage control (ex: RFMD3146) power amplifier ?
Is it a common phenomenon in PA design ? Thanks.

 

[vfone]

Re: GSM PA

Current consumption varies with load impedance on all the power amplifiers. On this phenomenon is based the load-pull characterization which consists essentially of measuring the power of a device, to a given specification as a function of input/output impedance. Data are measured at a large number of impedances and plotted on a Smith chart.
Load impedance for maximum power with lowest DC current consumption it gives maximum efficiency.
Maximum power and maximum efficiency not necessarily occur for the same load impedance.