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@ -1,14 +1,26 @@ |
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* Fourier Series Function for SPICE |
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* This script is offered here for learning purposes, even if it is outdated |
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* and superseeded by the spec function and especially by the much faster fft function. |
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* You may use this script in conjunction with e.g. a ringoscillator output (see |
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* the ngspice manual, chapter 17). |
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.control |
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begin |
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* Variable argc delivers the number of command line parameters given by the user |
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* after the 'spectrum' command |
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if ($argc lt 4) |
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echo Error: Too few arguments. |
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echo ' 'Spectrum produces a plot containing a fourier series transformation of |
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echo Error: Too few arguments. |
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echo ' 'Spectrum produces a plot containing a fourier series transformation of |
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echo ' 'the specified vectors |
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echo usage: spectrum startfreq stop step vec [[vec] ...] |
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goto bottom |
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end |
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* Check if vectors 'time' and any input vector(s) are available |
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* argv[n] delivers the command line entries after the 'spectrum' command, |
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* starting with argv[1]. $argv[4-len] delivers the value of all tokens, |
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* starting with postion 4 till the end of the command line |
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if ( time eq time ) |
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foreach vec $argv[4-len] |
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if ( $vec eq $vec ) |
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@ -21,63 +33,133 @@ |
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goto bottom |
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end |
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* generate a new plot entitled 'scratch', which will hold intermediate |
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* results and will be discarded after their evaluation. |
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set dt=$curplot |
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set title=$curplottitle |
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set curplot=new |
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set scratch=$curplot |
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* A vector 'span' is created in the 'scratch' plot to hold the time difference |
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* of the transient simulation. {$dt}.time allows to access the 'time' vector |
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* from the dt plot (which is normally named 'tranx' with x a consecutoive |
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* integer number, depending on the amount of transient simulations already run |
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* in the present job. |
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let span={$dt}.time[length({$dt}.time)-1]-{$dt}.time[0] |
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* Calculate the number of steps in all of the spectra to be evaluated below |
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if ($argv[3] gt 0.999/span) |
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let fpoints= ( $argv[2] - $argv[1] ) / $argv[3] +1 |
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if (fpoints < 2) |
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echo frequency start stop or step not correctly specified |
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goto cleanup |
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goto reset |
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end |
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else |
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echo Error: time span is not long enough for a step frequency of $argv[3] Hz |
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goto cleanup |
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goto reset |
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end |
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let lent = length({$dt}.time) |
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set lent = "$&lent" |
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let nyquist = {$lent}/2/span |
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if ($argv[2] gt nyquist) |
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echo Error: The nyquist limit is exceeded, try a frequency less than "$&nyquist" Hz |
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goto cleanup |
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goto reset |
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end |
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set fpoints="$&fpoints" |
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* generate a new plot to hold the spectra |
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set curplot=new |
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set spec=$curplot |
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set curplottitle=$title |
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set curplotname='Spectrum Analysis' |
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* argv[3] is the third agrgument from the input line |
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* spectrum 1 1000MEG 10MEG v(out25) |
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* that is the delta frequency |
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* The fcn vector(n) creates a vector of length n, its elements have |
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* the values 0, 1, 2, 3, ..., n-2, n-1. Each element then is multiplied |
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* with the frequency step value. |
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let frequency=vector( $fpoints )*$argv[3] |
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* Add an frequency offset to each element of vector 'frequency' |
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* to suppress the (typically) large dc component. |
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dowhile frequency[1] < ( $argv[1] + 1e-9 ) |
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let frequency = frequency + $argv[3] |
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end |
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* For each input vector given on the command line, |
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* create a new vector for complex numbers |
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foreach vec $argv[4-len] |
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let $vec = vector( $fpoints ) + j(vector( $fpoints )) |
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reshape $vec [{$fpoints}] |
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end |
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* $scratch is a plot for intermediate results, will be destroyed during cleanup |
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* $dt is the plot with the original data |
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* $spec is a plot for storing the spectrum |
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set curplot=$scratch |
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* some test |
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let npers=1 |
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let test = span-2/$argv[3] + 1e-9 |
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while test > 0 |
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let npers = npers + 1 |
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let test = test-1/$argv[3] |
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end |
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* Do the spectrum calculations |
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let ircle = 2*pi*max(-1,({$dt}.time-{$dt}.time[{$lent}-1])*{$argv[3]}/npers) |
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let win = 1 - cos(ircle) |
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let ircle = npers*ircle |
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let circle = ircle * ({$spec}.frequency[0]/$argv[3] - 1) |
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let k=vector( $fpoints ) |
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foreach k "$&k" |
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foreach k $&k |
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let circle = circle + ircle |
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foreach vec $argv[4-len] |
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let tmp = win*{$dt}.{$vec} |
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let tmp = win*{$dt}.{$vec} |
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let {$spec}.{$vec}[{$k}] = 2*(mean(cos(circle)*tmp),mean(sin(circle)*tmp)) |
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end |
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end |
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* plot (and write) the generated spectrum |
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set curplot = $spec |
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settype frequency frequency |
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foreach vec $argv[4-len] |
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let spectrum = mag({$vec}) |
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plot spectrum |
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write specout.out spectrum |
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end |
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* If you have an oscillator, fimd its frequency |
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* as maximum of vector spectrum or goto end (uncomment next line) |
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* goto cleanup |
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set curplot=$scratch |
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let counter = 0 |
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let contents = 0 |
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let freqmax = 0 |
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let spectrum = {$spec}.spectrum |
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foreach spectrum $&spectrum |
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if counter > 4 |
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if ( contents < $spectrum ) |
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let contents = $spectrum |
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set count = "$&counter" |
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let freqmax = {$spec}.frequency[{$count}] |
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end |
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end |
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let counter = counter + 1 |
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end |
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echo |
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echo Osc. frequency at "$&freqmax" Hz |
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echo |
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goto cleanup |
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label reset |
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set curplot=$dt |
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label cleanup |
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destroy $scratch |
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unset fpoints dt scratch spec vec k title lent |
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label bottom |
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end |
h_vogt
16 years ago