[sdiy] Spice/mathematical model of SSI2164

[Liam Wall]

The recent chat on simulations has got me playing with ngspice again,
and trying to set up a model of the SSI2164.

Previous discussion(1) suggests using the current gain formula from
the datasheet(2). I would like to have a model that can describe all
the facets of Fig 11 of the data-sheet --- the Temperature-Compensated
Exponential Voltage to Current Converter. This is the formula I'm
using so far

i = i(in) * exp(-qA*v(ctl) / (k*(temper+273.15)))

with qA/k being approx 1160.5. temper is the ngspice variable for the
device temperature.

But this model cannot explain VCA3 in fig 11, which is compensating
for the "series emitter resistance".

The text says the series emitter resistance should be modelled at
0.63R, then discusses that as applied to a transistor. I can follow
that logic to get to the ~0.75% error as it applies to the Ebers-Moll
equation. But not too sure how this should be factored into the model
for SSI2164.

Is it as simple as: tack a 0.63R resistor on to the output and
subtract the voltage drop from v(ctl) in the equation above?

Thanks, Liam.

(1) https://synth-diy.org/pipermail/synth-diy/2010-July/077934.html
(2) http://soundsemiconductor.com/downloads/ssi2164datasheet.pdf