To improve the efficiency, the PA can work in an energy saving mode. In this mode, an On-Off signal is used to turn the PA on or off. The PA is on when this signal is on, and is off when this signal is off. This signal can be called PA enable signal, which is a mask over the PA input signal.
To evaluate PA’s capability working in energy saving mode, EVM vs. Power measurement is designed. The general measurement flow in N7614B Signal Studio for Power Amplifier Test is as below.
The idle intervals are added to the selected waveform to form a new burst signal with specified duty cycle.
A PA enable signal is generated as a marker trace according to the parameters, T1,T3 and T4 and a burst signal is also generated using the selected waveform.
A power sweep is initiated. The average power of PA input or PA output sweeps with a fixed decrement in a specified power range. At each power level, the PA enable signal and burst signal are simultaneously applied as the PA power supply and the PA input respectively.
The PA output is connected to the Signal Analyzer and the EVM measurement is made.
Power vs. EVM trace is plotted as the final result.
The whole measurement process includes the following three parts.