Theory of Operation

The Power-Added Efficiency Measurement Library helps you set up PXI modules for synchronous RF pulsing, DC triggering, and DUT control to measure PAE, compression point, and gain.

Power-Added Efficiency

Power-added efficiency (PAE) is a measure of how efficiently a power amplifier converts a DC and RF input to a higher power RF output.

The following formula shows how PAE is calculated:

PAE=PRFoutputPRFinputPDCsupply

This calculation requires the power usage of the DC supply and the input and output powers on the ports of the DUT. To see how different frequency and power levels affect PAE, you can make several measurements across a sweep of frequencies or power levels. The data collected helps identify the ideal operating range of the DUT.

Compression Point Measurement

The compression point is the power level at which the amplifier enters a saturation region where the output power does not grow in proportion to the input power. In this scenario the proportion constant is equal to the gain of the amplifier.

The most common compression points are the 1 dB, 2 dB, and 3 dB points (often written as P1dB, P2dB, and P3dB). Although a device's actual response diverges from the theoretical response outside the linear range, P1dB is where the ideal linear response and measured data diverge by 1 dB.

The following graph shows an example of a PAE measurement with a compression point labeled.

Figure 1. Compression Points


Gain Measurement

Gain measurement determines the difference in power between the input and output of the device for each frequency. The gain is defined as:

Gain (dB)=10 log(PRFoutputPRFinput)=PRFoutput (dBm)-PRFinput (dBm)

It is measured in the linear range of the device, and it is obtained for each frequency, showing the gains over frequency or the gains over input power.