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Design >> Analog Design >> Different bias current! It is temperature-dependen
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Message started by nobody on Feb 11^th, 2004, 7:16pm

Title: Different bias current! It is temperature-dependen
Post by nobody on Feb 11^th, 2004, 7:16pm

Hi,
Is it possible to design a circuit that converts temperature to bias current?
The biasing current will be linear and have two different
slopes. The current will go from 100u(A) to 150u(A) between 25 and 50 degree C. The other slope will be two times as many as above slope. I know how to design a single slope but have no idea to design dual slopes. Thanks for you advice.

Title: Re: Different bias current! It is temperature-depe
Post by Mighty Mouse on Feb 12^th, 2004, 12:43am

A current source whose current is proportional to absolute temperature is referred to as PTAT, and there are many such current sources to choose from. To get a dual slope current source, consider simply building two PTAT sources, one with each slope, and summing their outputs. The outputs should be scaled so that the cross over occurs at the desired temperature.

- MM -

Title: Re: Different bias current! It is temperature-depe
Post by nobody on Feb 12^th, 2004, 7:27pm

Hi
Thanks for your help :D
I used PTAT current to design a reference voltage before and had the same idea as yours to solve this
problem. However, it is sort of weird.
The slope is flat between 0 and 25 degree C
and the slope is 2u(A)/degree C between 25 and 50 degree C. Then the the slope becomes 4u(A)/degree between 50 and 75 degree C. I am still trying to work out this puzzle. Hope you can understand what I say!
:-*

Title: Re: Different bias current! It is temperature-depe
Post by ywguo on Feb 18^th, 2004, 6:29pm

It is an interesting question. Why do you need convert temperature to two current sources with different temp slope?