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How Does the XDB Block Work?

The XDB block performs several different analyses.  The first analysis subtracts the specified XDB block GAIN_BACKOFF parameter from the input power level to compute the linear gain at every sweep point.  If compression is defined from maximum gain rather than linear gain then the next analysis uses optimization to find the maximum gain.  During the optimization, the input power starts at the input power level specified on the schematic and ramps up to find the maximum gain.  The last analysis uses optimization to find the specified compression.  During the optimization, the input power ramps up from the input power level specified on the schematic when compression is relative to linear gain and ramps up from the maximum gain point when compression is defined relative to the maximum gain.

That XDB Stuff Sounds Simple, So Why Am I Having Problems?

There are two likely problems with the XDB block.  The first is that during each optimization the input power is limited by the XDB block SCALE parameter.  Need some explanation of how to convert between linear scale and dB.  The second is that the optimization does not find the desired compression point before hitting the XDB block MAX_ITER number of iterations.  The good news is that both of these are easy to diagnose by inspecting the simulation output file link in the Status Window

How Do I Read The XDB simulation Output File

First, find the link to the output file in the Status Window (the Output - file link below) and click on it which will open the output file in AWRDE.

Simulation  - NLN:One_Tone_1_dB_Compression.AP_HB.$FDOC
10:41:19 AM   Begin Simulate
10:41:19 AM   Freq - 11 points
10:41:19 AM   Netlist - file://C:\My Dropbox\awr\appdata\jomoore\13.0\temp\High_Power_BJT_Amp(1)\NLN_One_Tone_1_dB_Compression.AP_HB.$FDOC\mwo_aplac_netlist.i
10:41:19 AM   Output - file://C:\My Dropbox\awr\appdata\jomoore\13.0\temp\High_Power_BJT_Amp(1)\NLN_One_Tone_1_dB_Compression.AP_HB.$FDOC\mwo_aplac_output.txt
10:41:20 AM   End Simulate (0.87s)

The first section of the file shows the input power used to find the linear gain and the linear gain values computed for each sweep point.  Any simulation warnings will appear only under the first sweep point.

                    APLAC 9.10 Wed Apr 05 2017 at 10:27:52
             Copyright (c) AWR-APLAC Corporation, Finland, 2005-
________________________________________________________________________________

FIND SMALL SIGNAL GAIN
POWER IN=-110.000 dBm

SWPVAL 1
LINEAR GAIN = 24.942 dB

APLAC 9.10 WARNING: Extrapolating up in frequency from 1 GHz to 1.1 GHz (_S1_S7_S1) 
APLAC 9.10 WARNING: Extrapolating up in frequency from 1 GHz to 1.1 GHz (_S1_S1_S1) 

SWPVAL 2
LINEAR GAIN = 24.505 dB

 
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SWPVAL 25
LINEAR GAIN = 22.818 dB

The next section of the file shows the max gain calculations.

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