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Design >> Analog Design >> PTAT current source design with configurable tempco
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Message started by jiesteve on Jan 8^th, 2009, 8:39pm

Title: PTAT current source design with configurable tempco
Post by jiesteve on Jan 8^th, 2009, 8:39pm

I need to design a PTAT-like current source with a configurable tempco. I need the current to increase with increasing temperature. The circuit cannot be trimmed at two temperature points, so I would like the tempco to be based on a ratio of matched resistors/devices. Is this possible? If so, could you give me some pointers and/or references?

Thanks!

Title: Re: PTAT current source design with configurable tempco
Post by Berti on Jan 9^th, 2009, 4:04am

Just an idea: Use a bandgap. Instead of completely canceling the tempco adjust it in a way that it fits the wanted tempco. I think in a bandgap this is done by resistor ratio which can easily be reconfigured.

Regards

Title: Re: PTAT current source design with configurable tempco
Post by Nimrod Ben-Ari on Jan 13^th, 2009, 5:16am

another option is using a sub-threshold current source, trimming the resistor would change the temperature dependency.

Nimrod

Title: Re: PTAT current source design with configurable tempco
Post by ywguo on Jan 26^th, 2009, 5:00am

Hi Jiesteve,

Either the bandgap based on BJTs or sub-threshold current source, the PTAT (Proportional To Absolute Temperature) derives from a voltage difference that is PTAT. The PTAT voltage is applied on both terminals of a resistor, so PTAT current flows through the resistor. Don't forget that the resistor always has non-zero temp coeffecient whatever it is made of, like nwell, poly, and diffusion.

Nonetheless, you might make a resistor made of more than one type of material, one with positive temp coeffecient, the other with negative temp coeffecient. They are put in series or parallel. Choose the ratio of both type of material to let the the combined resistor is of zero temp coeffecient. Just try it. Good luck.

Yawei