[sdiy] LTspice - exponential voltage curve

[Neil Johnson]

Justin,

In future it would REALLY help if you ask what you actually want.  In
this case it's an easy bit of mathematical manipulation to come up
with the right exponent formula to plot what you want:

V=5*exp(3.466*(time-1))

Neil

On 29 October 2013 16:15, Justin Owen <juzowen at gmail.com> wrote:
> 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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>
>
>
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