How to plot AM/AM and AM/PM Characteristic using input and output baseband signals?

I have .txt files that contain complex input and output baseband signals of an amplifier. I need to plot the AM/AM (magnitude of Gain vs. Input power) and AM/PM (phase of Gain vs. Input power) Characteristic.

% Calculate input and output power
P_in = 30 + 10*log10( (abs(x_in).^2)/100); % x_in is the input baseband signal 
P_out = 30 + 10*log10((abs(x_out).^2)/100); % x_out is the output baseband signal
% Calculate gain
Mag_Gain = P_out - P_in;
Phase_Gain = rad2deg((angle(x_out) - angle(x_in)));

% Then I plot the AM/AM and AM/PM curves
% however the results does not match with the theoretical results.
% Is the way for calculating the power correct?

[Laxmikant]

Hi Zainab,

Have you find the right way to to get AM-AM plot and AM-PM plot?

could you share your result?

I also have PA input singal and output signal from PA but not sure I am doing things in right way or not. My AM-AM plot is spread over large area.

Thank you.

Answer 1

[Aditya]

Hi Zainab,

There's limited information to fully address your query, but from the equations you've shared, your calculations for power seem correct. Here are a few things you might consider to resolve the issue:

1. Check Unit Consistency: Ensure that all units (e.g., dBm, dB) are consistent throughout your calculations.
2. MATLAB Central Resource: You might find this MATLAB Central File Exchange post helpful: https://www.mathworks.com/matlabcentral/fileexchange/173930-plots-am-am-and-am-pm?s_tid=answers_rc2-1_p4_MLT

If this doesn't resolve the issue, please attach the output that you are getting and the theoretical output.

[Zainab Riyadh]

Thank you for your response.

Is there documentation for building digital predistortion Lookup tables based on LUT of the PA and gain?