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Analoger

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Application of on-chip bandgap
Aug 29^th, 2005, 8:47pm

Hello guys,
I've designed two bandgap blocks, but I have never actually used them in any A/D converters or biasing circuits. Can anyone of you provide some examples on how to use a bandgap in a "larger" circuit system?

Apperentaly bandgap itselt doesn't have any driving capability. I assume a follower or some kind of gain amplifier will be needed. For examples, if a bandgap is included on the same chip with a pipelined ADC (to generate the Vref), usually how do people implement it? A circuit diagram would be appreciated! Thank you!

Andy

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Paul

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Switzerland

Re: Application of on-chip bandgap
Reply #1 - Aug 30^th, 2005, 1:28pm

Hello Andy,

it is preferrable to use a buffer amplifier to deliver the bandgap voltage to the reference voltage input of an A/D converter, especially if the latter is built with switched capacitors. Obviously any gain error, mismatch, flicker noise, PSRR and temperature drift in the above parameters adds to the bandgap reference's intrinsic imperfections.

I currently don't have any papers at hand, but you should be able to find some hearing aid or data conversion system papers in the IEEExplore search engine.

Paul

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Analoger Junior Member Offline Posts: 15	Re: Application of on-chip bandgap Reply #2 - Aug 30^th, 2005, 8:01pm Hi Paul, Thanks for your reply. It'll be greatly appreciated if you (and other senior design members) could supply some examples of using a on-chip bandgap in: 1. ADC/DAC: as reference for the resistor ladder or SW ref for pipelined adc 2. Biasing block 3. As reference voltage for amplifier Thank you! Andy
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Analoger Junior Member Offline Posts: 15	Re: Application of on-chip bandgap Reply #3 - Sep 15^th, 2005, 2:44pm Anyone? Thanks! -Andy
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Paul Community Fellow Offline Posts: 351 Switzerland	Re: Application of on-chip bandgap Reply #4 - Sep 16^th, 2005, 1:13pm Andy, I don't know what exactly you are looking for... If you formulate a concrete question, somebody may be able to answer it. If you would like to have paper references, Google and IEEExplore are probably more efficient than humans. Paul
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Analoger Junior Member Offline Posts: 15	Re: Application of on-chip bandgap Reply #5 - Sep 25^th, 2005, 10:46pm I would like to see a direct application of the bandgap in a "larger" system, such as how it's been used in data converters, amplifiers etc. TIA!
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sheldon

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Posts: 751

Re: Application of on-chip bandgap
Reply #6 - Sep 29^th, 2005, 5:28am

Analoger,

How about creating a V/I converter using the Bandgap
Reference as the input. The Bandgap is tied to the
non-inverting input of the V/I converter op-amp. The
The V/I output current becomes the reference current
for the D/A Converter. If the DAC load resistors are made
from the same material as the V/I reference resistor.
Then the resistor process variation cancels to the first
order and temperature drift cancels to the first order. So
the output voltage level/swing is stable and determined
by the ratio of the V/I converter reference resistor to the
load resistor and the value of the Bandgap Reference.
The principle also works for generating stable reference
voltages for an ADC. In a pipeline ADC each stage needs
a reference voltage. You can either route a supply
voltage all round the ADC and risk contamination. Or
you can create reference voltages in each block.

Best Regards,

Sheldon

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Analoger Junior Member Offline Posts: 15	Re: Application of on-chip bandgap Reply #7 - Sep 29^th, 2005, 7:24pm Very nice said, Sheldon. Thank you!
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