[sdiy] LTspice - exponential voltage curve

[Justin Owen]

Still not having any luck with this.

I've tried scaling the arb voltage based on a 5V ramp using V=exp(V(Ramp)/2.8)-1 where (Ramp) is a 5V Pulse that ramps up from 0V to 5V across 1 second.

I've tried scaling exp() against time V=exp(1.7917*time)-1.0 and a variation on Neil's suggestion of V=exp(time/0.56)-1.

These all give pretty much the same results - but none of them have the exact curve I'm looking for which is:

0s = 0V (OK 0V = 0.15625)
0.2s = 0.3125V
0.4s = 0.625V
0.6s = 1.25V
0.8s = 2.5V
1s = 5V

Any other suggestions? Thanks.

-----Original Message-----
From: Neil Johnson [neil.johnson71 at gmail.com]
Received: 28.10.2013 15:19:41
To: Justin Owen
Cc: SDIY List
Subject: Re: [sdiy] LTspice - exponential voltage curve

Use an arbitrary voltage source and set the equation to use "exp()"
with some time-based function.  E.g. "V=exp(time/100)".

Neil

On 25 October 2013 16:52, Justin Owen <juzowen at gmail.com> wrote:
> Hello,
>
> Taking my first few steps with LTspice. I'm simulating a simple Linear to Exponential converter running a VCA. I'm scoping/probing the sine wave output of the VCA.
>
> For the linear current source I could run a scope of the linear CV input as it ramped from 0V to 2.5V and graph that against the VCA output to check it's linearity - now I'd like to have a similar exponential voltage source to graph the VCA output against using the Lin/Exp converter.
>
> How would I do that in LTspice?
>
> Got sort of close with an arbitrary voltage source reading of a linear source.
>
> Thanks!
>
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