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nemethakos
modified 9 years ago

EC transistor model has no intrinsic emitter resistance

1
10
79
02:15:47
It seems that EC's transistor model lacks the intrinsic emitter resistance, so no barn-roof distortion is visible in the output of the grounded emitter amplifier. Mr. Ebers and Mr. Moll are very unhappy about this!
published 9 years ago
thebugger
9 years ago
It has emitter resistance. Check the transistor settings.
BillyT
9 years ago
Maybe a current limiting base resistor might help also, 4+ Amps base current is a bit raw.
nemethakos
9 years ago
From the Ebers-Moll model, the "resistance" at the emitter is re=Vt/Ic (Vt is the thermal voltage which is 25.3 at room temperature, Ic is the collector current in mA). For example if Ic=1mA, the emitter resistance is 25Ω, if Ic=10mA, re=2.5Ω. The amplifier has higher gain at lower Ic and this would distort the output waveform: http://images.slideplayer.com/15/4569883/slides/slide_8.jpg
thebugger
9 years ago
You can adjust the parameters manually if you want
zorgrian
9 years ago
How seriously does this affect most circuit simulation? Also do spice software packages have intrinsic emitter resistance? If so, please let us know which spice packages to use to demonstrate the non obvious effect of this psudo problem
zorgrian
9 years ago
As ze buggy bugger points out your assertion is not true. I can adjust the emitter resistance
zorgrian
9 years ago
The first semiconductors were limited to light sensor action and heat
thebugger
9 years ago
And remember that this is an ideal environment, as are all the components here.
nemethakos
9 years ago
It is not public which model is used in EC for the BJT, but guessing from the available parameters ( forward current gain, reverse current gain, reverse saturation current ) it is the "unapproximated Ebers–Moll equations" as wikipedia calls it: https://en.m.wikipedia.org/wiki/Bipolar_junction_transistor#Ebers.E2.80.93Moll_model What is missing for me is the modelling of the Early effect: https://en.m.wikipedia.org/wiki/Bipolar_junction_transistor#Base-width_modulation ( Why? because I want to simulate circuits from Art of Electronics which are dealing with the problem of the collector current dependence of forward beta or gain ). SPICE variants uses the Gummel-Poon model which have too many parameters for a mobile based simulator like EC to handle ( and there is no screen eastate for setting 41 different transistor parameters ). The resistance values which can be manually set are not part of any of the models used for modelling BJTs, so they could be Igor's fix to avoid "cannot find solution" errors.
nemethakos
9 years ago
Gummel-Poon model and SPICE parameters: https://en.m.wikipedia.org/wiki/Gummel–Poon_model

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