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lhlbluesky_lhl

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about temperature coefficient of bandgap
Dec 05^th, 2011, 4:07am

i have designed a bandgap in 0.18um 0.33V process, which is the classic structure (an opamp, two bjt of 1:8, a pmos pair, and a resistor), VREF=VEB+VT*ln8/R1*R2, but the tc is 45ppm for the simulation. i used some methods to improve the tc, such as exp compensation, different type of resistors (different tc, one is positive, one is negative), and so on, but it only improves a little. in some papers, i see the compensated bandgap can have a tc of 5ppm or below, but how to achive this in actual case? or how to do curvature compensation for bandgap in real project design?

thanks all in advance.

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Lex Senior Member Offline Posts: 201 Eindhoven, Holland	Re: about temperature coefficient of bandgap Reply #1 - Dec 5^th, 2011, 5:39am Use trimming.
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: about temperature coefficient of bandgap Reply #2 - Dec 5^th, 2011, 9:41am start putting offsets and mismatches into your simulation. You will see that you will need to trim and adjust the device. Also, look up the topic "chopper offset cancellation" or "chopper stabilized op-amps" - this is one way to deal with offset issues.
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RobG

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Re: about temperature coefficient of bandgap
Reply #3 - Dec 5^th, 2011, 11:10am

I think he wants to know how to remove the curvature (about 4 mV) from a traditional bandgap response, i.e. he wants a decent curvature correction circuit. There are countless ways that look great in simulation but they have problems over corners and mismatches which are hard to correct with a single temperature trim in silicon. Amazingly, I still see a lot of new patents popping up on this ancient subject!

IMO, the most robust are independent of the bandgap reference itself and are a piecewise linear correction. At room temp they do not change the performance (so the zero temp-co output voltage is still ~1.23 V). However at temps greater than room they add a PTAT voltage, and at temps colder than room they add a CTAT voltage. �

An current mode example is published by Rincon-Mora JSSC, Oct 1998. http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=720402

You can adapt the PWL correction to the "normal" bandgap. Just inject the PWL current into the 1x pnp emitter. It might help to see how it was done in one of my patents 6,642,699

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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: about temperature coefficient of bandgap Reply #4 - Dec 6^th, 2011, 2:24am yes he wants a "curvature compensated bandgap" (search IEEE JSSC for those terms) - but the other items in mismatch and offset must be fixed first, because they are much larger than the thermal curvature.
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lhlbluesky_lhl Senior Member Offline Posts: 115	Re: about temperature coefficient of bandgap Reply #5 - Dec 6^th, 2011, 4:17am thanks all.
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RobG

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Bozeman, MT

Re: about temperature coefficient of bandgap
Reply #6 - Dec 6^th, 2011, 6:56am

loose-electron wrote on Dec 6^th, 2011, 2:24am:

yes he wants a "curvature compensated bandgap" (search IEEE JSSC for those terms) - but the other items in mismatch and offset must be fixed first, because they are much larger than the thermal curvature.

I agree - that is what gets most people. He can search for my CICC paper on that too Wink

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