SV: Re: [sdiy] PAIA VCO, LM13700 diode temp comp.

[Simon Brouwer]

Hi Karl, all,

karl dalen wrote:

>--- Ian Fritz <ijfritz at earthlink.net> skrev:
>
>  
>
>>At 05:42 PM 10/17/05, karl dalen wrote:
>>    
>>
>>>Long time ago there was discussions on the PAIA
>>>VCO temp drift compensation using the diodes of
>>>the LM13700, how did that turned out?
>>>
>>>Was it a good idea of temp compensation?
>>>      
>>>
>>I built a similar VCO a few months ago, as an aux VCO to use in my chaos 
>>box.  My main trouble with this circuit involved the V/Oct tracking.  After 
>>much experimenting and tweaking the best tracking I got was +/- 0.5% from 
>>100 Hz to 6 kHz.  Nothing even close to the 2 cents accuracy claimed in the 
>>writeup.  I didn't check the temperature drift.  It shouldn't be too bad, 
>>but I know from another active-compensation circuit that you need good 
>>matching of the OTA pair.
>>    
>>
>
>Wich would be a pain! I have never found any pair that have matched each
>other!!
>
>  
>
Hmm, according to the data sheet of the LM13700, the variation of gm can
be 6700 to 13000 mmho, almost a factor 2.
However, gm tracking (between the OTAs in one package) is 0.3 dB
typical. That would be about 3.5% mismatch.


-- 
Vriendelijke groet,
Simon Brouwer.

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