[sdiy] V/Oct accuracy

Roman Sowa modular at go2.pl
Mon Dec 3 16:40:54 CET 2018


I usually don't pay attention to Initial Accuracy, as this is always 
later trimmed in hardware or software. What's most important for me are 
temperature stability and long term drift. You may be limiting your 
choices if you focus on Initial Accuracy.

Why do you want to avoid trim? Is it going to be manufactured in 
thousands? If you don't want trimpots, then maybe try non-volatile 
digital pot instead.

And since it's VCO, then maybe add a little microcontroller and 
autotune/autocalibration routine. Maintaining frequency by means of smal 
cheap crystal is easier than maintaining precision voltage over long 
period, so then you could use ultra cheap reference.

Roman

W dniu 2018-12-03 o 16:12, Tim Ressel pisze:
> Good morning,
> 
> I am designing a triangle core VCO and have come to the part of the show 
> where I get to pick a voltage reference chip. As I'm sure you're all 
> aware the cost goes up as accuracy increases. Initial accuracy I mean, 
> as I am trying to avoid a trim. This reference will set the amplitude of 
> the wave as well as serve as a voltage for a range switch which needs to 
> set exact (?) octaves. So the question is: how much accuracy do I need 
> to pay for?
> 
> The issue is complicated by the fact that the customer is "west coast" 
> and shuns all notions of notes. But as I see it, volt per octave has a 
> certain meaning and sets up certain expectations. For example, the 
> octave switch should jump the oscillator 1 octave +/- some acceptably 
> small error.  In my meanderings I concluded the error should be 6 cents 
> or less.
> 
> The issue is further complicated by my catching the accuracy bug during 
> my stint at what is called Keysight this week. I tend to err on the side 
> of minimizing err ;-)  It is an expensive obsession to be sure, and as 
> it is my customer that has to pay for it, I need to strike a balance. I 
> know there is also drift and resistor tolerances to consider. One battle 
> at a time.
> 
> Thoughts?
> 



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