Guest essay by Leo Smith – elevated from a comment left on WUWT on January 6, 2015 at 2:11 am (h/t to dbs)
As an engineer, my first experience of a computer model taught me nearly all I needed to know about models.
I was tasked with designing a high voltage video amplifier to drive a military heads up display featuring a CRT.
Some people suggested I make use of the acoustic coupler to input my design and optimise it with one of the circuit modelling programs they had devised. The results were encouraging, so I built it. The circuit itself was a dismal failure.
Investigation revealed the reason instantly: the model parametrised parasitic capacitance into a simple single value: the reality of semiconductors is that the capacitance varies with applied voltage – an effect made use of in every radio today as the ‘varicap diode’. for small signals this…
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