How do I calculate the input power into the amplifier when using the RF Blockset?

I am using RF Blockset to simulate the distortion characteristics of an RF amplifier and want to calculate the input power relative to the third order intercept point needed to maintain distortion below a certain amount.

Given a third order intercept point, this is relatively simple to calculate manually if just considering two tones, however RF Blockset allows one to simulate with multiple arbitrary tones and I am using it with a 64QAM input.

What is the reference impedance?

Answer 1

[MathWorks Support Team]

For Simulink signals, we assume by default the nominal 1 ohm impedance used by communication engineers (see attached example) where signal amplitudes are represented as binary numbers in DSP or FPGA implementation.

amp_qam16_with_powerhead.mdl

However, RF Blockset physical blockset supports more physically based impedances. For a full explanation of how the Input Port and Output blocks acts a gateway between nominal 1 ohm Simulink signals and physically based impedances, please see section "Key Blockset Concepts -> Interpretation of Simulink Signals" in the RF Blockset documentation.

If another impedance is desired, the best practice is to define a constant in the Base Workspace (MATLAB variable) by executing the following

Z0 = 50 % ohms

 or in the Model Workspace ( define a Simulink parameter) and use that as a parameter in all amplitude settings in the source blocks. See attached example where this is illustrated:

power_examples.mdl