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{\rtf\ansi \deff0{\colortbl;\red0\green0\blue0;}{\fonttbl{\f0\fcharset0
\fnil Arial;}}\plain\cf1\fs24 \pard TANH FUNCTION SINE SHAPER--SEAT OF 
THE PANTS VERSION\par \par \par Phil Hobbs\par \par ElectroOptical 
Innovations \par March 8, 2010\par \par The strategy here is to 
generate a tri wave, then bung it into a BJT diff pair to curve it 
over a bit, and subtract a bit of the original tri wave to get rid of 
the cusps.  To realy optimize this you want to compute the THD as a 
function of the amplitude going into the tanh shaper and the amount of 
tri wave subtracted, but that's too much like work for a 
sci.electronics.design post!}
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{\rtf\ansi \deff0{\colortbl;\red0\green0\blue0;}{\fonttbl{\f0\fcharset0
\fnil Arial;}}\plain\cf1\fs24 \pard The tanh shaper (even in this 
poorly optimized version) gives about 0.5% THD, predominantly third 
harmonic.  Higher harmonics go away nearly completely due to 
cancelling the cusp.}