Distortion Analysis

Distortion analysis controls whether SPICE computes the distortion characteristic of the circuit in a small-signal mode as a part of the AC small-signal sinusoidal steady-state analysis. The analysis is performed assuring that one or two signal frequencies are imposed at the input; let the two frequencies be f1 (the nominal analysis frequency) and f2 (=SKW2*f1). The program then computes the following distortion measures, which can be printed or plotted:

• HD2 - the magnitude of the frequency component 2*f1 assuming that f2 is not present
• HD3 - the magnitude of the frequency component 3*f1 assuming that f2 is not present
• SIM2 - the magnitude of the frequency component f1 + f2
• DIM2 - the magnitude of the frequency component f1 - f2
• DIM3 - the magnitude of the frequency component 2*f1 - f2

DR. SPICE takes in both SPICE2 and SPICE3 formats for distortion analysis.

SPICE2 general format:

.DISTO RLOAD <INTER <SKW2 <REFPWR <SPW2>>>> 

Example:

.DISTO RL 2 0.95 1.0E-3 0.75 

The following list describes each abbreviation:

• RLOAD = the name of the output load resistor into which all distortion power products are to be computed.
• INTER = the interval at which the summary printout of the contributions of all non-linear devices to the total distortion is to be printed. If omitted or set to zero, no summary printout will be made.
• REFPWR = the reference power level used in computing the distortion products; if omitted, a value of 1 mW (that is, dbm) is used.
• SKW2 = the ratio of f2 to f1. If omitted, a value of 0.9 is used (i.e., f2 = 0.9*f1).
• SPW2 = the amplitude of f2. If omitted, a value of 1.0 is assumed.

SPICE3 general format:

.DISTO {DEC/LIN/OCT} NP FSTART FSTOP <F2_OVER_F1> Vname n+ n- . . . DISTOF1 <MAGNITUDE> 
<PHASE> + DISTOF2 <MAGNITUDE> <PHASE> 

Example:

.DISTO DEC 5 100 10MEG 0.9 
Vs 1 0 AC 1 DISTOF1 1.0 0.0 DISTOF2 0.1 -90 

The following list describes each abbreviation:

• DEC = decade variation
• LIN = linear variation
• OCT = octave variation
• FSTART = starting frequency
• FSTOP = final frequency
• Vname (or Iname) = the voltage (or current) source, N+ and N- = positive and negative nodes, respectively.

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