[sdiy] Spice simulation of diff amp

[ASSI]

On Thursday 06 February 2014, 19:36:30, Rutger Vlek 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 nutshell, there isn't a single variable in a BJT model that directly 
changes Vbe.  But, depending on what you want to simulate you can fake it 
with low to moderate effort: if the bias point is almost constant, just add 
a voltage source that models your mismatch to one of the transistor bases.  
A slightly different approach is to put one of the transistors at a 
different temperature (delta Vbe ~ 2mV/K).  This works well for small 
differences and is better for large changes in biasing, but of course it 
changes quite a bit more than just the Vbe.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Factory and User Sound Singles for Waldorf Q+, Q and microQ:
http://Synth.Stromeko.net/Downloads.html#WaldorfSounds