[sdiy] LM13700 as VC resistor

Didier Leplae didierleplae at yahoo.com
Sun Feb 9 02:25:20 CET 2020


René,
Sorry for my ignorance, but when you say “ Use Iabc to get gm (19.2*Iabc = gm), and the rest should be easy.”

What is “labc”?

> On Feb 8, 2020, at 11:51 AM, René Schmitz <synth at schmitzbits.de> wrote:
> 
> Hi Didier and all,
> 
>> On 08.02.2020 10:58, Didier Leplae via Synth-diy wrote:
>> I am curious to know anyone’s opinions on using the LM13700 as a voltage controlled resistor.
>> The LM13700 datasheet has a couple schematics which I have tried building, with mixed results. I’m having a hard time knowing what sort of resistance I am getting as the multimeter gives strange and inconsistent readings.
>> The information on the datasheet is somewhat incomplete in my opinion and it is not easy to find much info online either.
> 
> Yes, it doesn't tell you the fact that the resistor is AC coupled (single ended circuit). See the Cap at the output...
> So poking around with a multimeter is not going to give meaningful results.
> But the formula for Rx is given. Use Iabc to get gm (19.2*Iabc = gm), and the rest should be easy.
> 
> 
>> It doesn’t seem like it is common practice to use these as VC resistors. Is that because it doesn’t work very well? Or use too many parts?
> 
> Wouldn't be my first choice due to complexity and parts count.
> 
> Best,
> René
> 
> --
> synth at schmitzbits.de
> http://schmitzbits.de





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