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Design >> Analog Design >> NEGATIVE Temperature Coefficient
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Message started by Mayank on Dec 10^th, 2009, 4:33am

Title: NEGATIVE Temperature Coefficient
Post by Mayank on Dec 10^th, 2009, 4:33am

Hi,
I need a CTAT [Complementary to Absolute Temperature] current for Temperature compensation [ i.e. a Negative temperature coefficient ].
For Temperature compensation of my Oscillator, I require a CTAT current coefficient α of around -1mA/A/K
[ α as in the equationI_actual = I_nom * (1 + α*ΔT)] . Means a 5uA decrease in a 100uA bias current for 50 ^∘C change in Temperature.

Any suggestions ?? I doubt that a CTAT Bandgap will provide such high CTAT current coefficient ? Can anyone Help ?

--mayank.

Title: Re: NEGATIVE Temperature Coefficient
Post by ACWWong on Dec 10^th, 2009, 2:29pm

A standard CTAT will do. i.e. using a bjt vbe which is about -1~-2mV/^oC, you can use an op-amp to make a current in resistor follow this voltage.

So from say 300K to 350K you'll get about a vbe drop of say 700mV to 600mV (obviously depending on technology and current density etc.), which is much better than the 5% you need.

cheers
aw