[sdiy] Spice simulation of diff amp

[Rutger Vlek]

Thanks Tim! I'll have a look at the books.

Anyone else have experience Monte Carlo-ing Vbe matching in Spice?

Best,

Rutger


On 6 feb 2014, at 23:11, Tim Stinchcombe wrote:

>> I'm trying to simulate a differential amplifier circuit in 
>> Spice and hope to be able to run a Monte Carlo test that 
>> allows me to see how various circuit properties respond to 
>> component tolerances. I have an differential pair of 
>> transistors that I figured out how to simulate current gain 
>> variations (within a certain matching accuracy) for, but I 
>> don't know how to do this for Vbe matching. Does the Spice 
>> BJT model have a parameter that corresponds directly to Vbe, 
>> such that I can use this to simulate matching of Vbe within a 
>> certain range? Or is this a case of: move to reality instead 
>> of the virtual domain? :).
> 
> In a word, 'no'. SPICE uses the Gummel-Poon model, which has about 40
> parameters to play with:
> 
> http://en.wikipedia.org/wiki/Gummel%E2%80%93Poon_model
> 
> but that link doesn't actually give the equations! This here looks to be an
> early(ish), original SPICE document:
> 
> http://www.ece.umn.edu/~harjani/courses/common/spice2G6.pdf
> 
> and the equations are given near the end. So you'll probably have to juggle
> with things like saturation current, IS, and emission coefficient, NF
> instead of 'Vbe' (others around here must surely have dabbled in this, so
> hopefully they will speak up...?). There is tons of stuff about SPICE BJT
> parameters out there on the net just waiting to be found, or grab a couple
> of books - I particularly like 'SPICE: Practical Device Modeling' by
> Kielkowski as it shows how to obtain these parameters from actual measured
> curves taken from devices, which of course you can _simulate_ and then see
> how altering the parameters affects the normal BJT-type curves that many of
> us are more used to dealing with. The other book I frequently refer to for
> such matters is 'The SPICE Book' by Valdimirescu, which is a fairly
> down-to-earth book about SPICE and gives the parameters and equations in
> appendices, again in a fairly concise manner.
> 
> Tim
> __________________________________________________________
> Tim Stinchcombe 
> 
> Cheltenham, Glos, UK
> email: tim102 at timstinchcombe.co.uk
> www.timstinchcombe.co.uk
> 
>