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[Moved]: Voltage to Current Converter

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wturtle

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Hey guys,

I need a few suggestions. I built a bandgap that has an output of around 600mV. But now I need to use this voltage and create a current reference that is also PVT independent, or at least, tracks the bandgap voltage good enough.

I've seen a few circuits in which we simply use a amplifier with negative feedback and force the bandgap voltage across a resistor. But the single resistor varies a lot with process corners and introduces a lot of error.

I need a few sugestions!
Can you provide a few articles or something?

Thanks,
 

erikl

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Re: Voltage to Current Converter

You could either spring for an external NP0 resistor - which costs you a pad - or you could try and put an internal resistor together applicatively from available resistors with positive and negative temperature dependencies, as to compensate this as well as possible.

V independence you can get by using the bandgap voltage. But of course you can't avoid the P variance - this would need individual trimming.
 

wturtle

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This poses a few problems.
1.Can't use external resistors.
2.Only have one type of resistors so no neg or pos TCs.
3.Can't do trimming either.

The bandgap topology itself is process "independent" due to R2/R1 resistors ratios. The ratio eliminates corner dependecny and lowers mismtach as well. I wanted some type of topology similar to that (based on ratios) but to current, using the bandgap as reference.
 

erikl

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You could try a so called CTAT current source (a temperature compensated PTAT current source), s. Circuit 3 & 4 of this image (general representations):
pseudo_PTAT_and_CTAT_current-sources.png

Here is such a circuit: Low-current_low_TC_constant_current_source.png - but unfortunately it doesn't work better than -1000 ppm/K.

I also tried this one: VTcompCCref.png, but with no better success.

Good luck!
 

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