[sdiy] Expo VCOs: some thoughts

[Tim Ressel]

My customer is concerned over some imagined backlash over a fight 
between the cloners and the original CES folks. I don't know...

--timmers


On 5/21/2018 2:06 AM, paula at synth.net wrote:
> Why not go for the AS3340?
>
> Paula
>
> On 2018-05-20 19:58, Tim Ressel wrote:
>> Happy Sunday! And by Sunday I mean the sun is out today...
>>
>> I've been thinking about volt/octave VCO performance. My customer
>> wants a triangle core VCO with excellent tracking. And of course he
>> wants it for $0.25, but that's another story. I started looking at
>> expo VCO design from the standpoint of tracking. Typically there are
>> two pieces to an expo VCO: the expo converter and the VCO core, and
>> they can be looked at separately. I'm going to tackle the core side
>> because that is where the problems are with triangle cores.
>>
>> I looked at two designs: LM13700 and 4046. The focus is on linearity
>> between the control current and the resulting frequency. There are
>> other issues, but I feel linearity is the biggest. In an ideal core
>> the linearity would be perfect, but as I looked at the datasheets it
>> became clear these were not ideal. Both the 4046 and the 13700 are not
>> so great for linearity. Don't get me wrong; they are okay devices. It
>> just that our performance needs are beyond their capabilities. It's
>> not their fault.
>>
>> So now I am looking at a switched current mirror type design similar
>> to that found in the venerable 566. I believe the non-linearities will
>> be reduced to opamp, capacitor, and comparator issues. That's all,
>> just that ;-)
>>
>> My customer also needs a small footprint as we are trying to cram 4 of
>> these on one board. As a great boss once told me: "Size, price,
>> performance: Pick any two."
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy
>

-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com