Triangle VCO current source?

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BWBKc6VyUr
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Triangle VCO current source?

Post by BWBKc6VyUr » Wed Jan 13, 2021 10:59 am

What’s the least exotic part available nowadays for the reversible charging current source of a triangle VCO core?
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ljwall83
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Re: Triangle VCO current source?

Post by ljwall83 » Wed Jan 13, 2021 11:10 am

Is the LM13700 exotic?

Short of building one out of transistors, I'd also like know if there is something better out there.

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devinw1
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Re: Triangle VCO current source?

Post by devinw1 » Wed Jan 13, 2021 11:44 am

Yeah, a OTA such as the LM13700, CA/AS3280 or a current-output VCA like the 2164 are probably the most common and least exotic.

ljwall83
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Re: Triangle VCO current source?

Post by ljwall83 » Wed Jan 13, 2021 1:22 pm

I asked about the 2164 as a current sourse for a triangle VCO before and was advised by Neil Johnson that's it not ideal to use that way, and as per the data sheet is best kept as current sink, like in the expo converter in the ssi data sheet. (Must confess the reason were above me however.)

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Re: Triangle VCO current source?

Post by guest » Wed Jan 13, 2021 6:36 pm

the 2164 should work ok. perhaps neil assumed you were going to drive the capacitor directly, but if you use an opamp integrator sinking and sourcing should both be fine. the input stage has DC accuracy issues due to offset voltage/current, but i dont think its a show stopper. but, the 13700 is a more widely available part, and is cheaper. it also allows you to more accurately control the expo converter. theres pros and cons to each.
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BWBKc6VyUr
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Re: Triangle VCO current source?

Post by BWBKc6VyUr » Thu Jan 14, 2021 3:13 pm

Of the parts suggested above, which is least likely to go out of production in the near future? (i.e. is commonly used in mass produced systems like mobile phones, home appliances, etc. ?)
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Re: Triangle VCO current source?

Post by guest » Thu Jan 14, 2021 8:06 pm

neither are widely used parts, but are both likely to be around for quite some time. i feel like the LM13700 might outlast the 2164, but thats still going to be at least another 20 years from now. a discrete transistor approach would be the only one guaranteed to not go out of production, as you can swap in different transistors as needed.
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