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Mayank Community Fellow Offline Posts: 334	Re: Stable Iref across PVT Reply #15 - Jun 16^th, 2010, 9:04pm Agree with RobG here. But in VBG / Rztc, it's difficult to obtain compensated umbrella across Process Corners. In BGR Core ZTC Iref Generation, the umbrella shape is more or less preserved across Process Corners.
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newic Senior Member Offline Posts: 138	Re: Stable Iref across PVT Reply #16 - Jun 19^th, 2010, 8:47pm it is nice to cancel out the positive TC (PTC) resistor with negative TC (NTC) resistor to get independent temperature. However, the process variation of these two resistors might be different. Unless both the PTC & NTC resistors are the same type (poly type) BUT poly resistors are PTC type.
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newic Senior Member Offline Posts: 138	Re: Stable Iref across PVT Reply #17 - Jun 19^th, 2010, 8:54pm Quote: Inside BGR core -- < 50uA Inside Current References core -- < 100uA Could you explain these BGR core & Current references core. I think i might be confused. It is great if the pictures or papers are shown.
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Mayank

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Re: Stable Iref across PVT
Reply #18 - Jun 20^th, 2010, 10:53am

Typical BGR core consists of a normal ΔVBE + VT*ln(n) compensation.
or in other words, VBE1 = VBE2 + Iptat*R.

Typical Current Reference Core, includes extra Resistance arms connected in parallel with the branches of a BGR core to provide CTAT current, which then adds up with PTAT current generated by the BGR core, thus providing ZTC current.

Pls. Refer Voltage References by Gabriel Rincon Moora.

--M

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RobG

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Re: Stable Iref across PVT
Reply #19 - Jun 20^th, 2010, 9:26pm

newic wrote on Jun 19^th, 2010, 8:47pm:

it is nice to cancel out the positive TC (PTC) resistor with negative TC (NTC) resistor to get independent temperature.

However, the process variation of these two resistors might be different. Unless both the PTC & NTC resistors are the same type (poly type) BUT poly resistors are PTC type.

Actually not necessarily true about the process variation... read the paper I referenced. It shows how to make composite resistors so that the independent sheet resistance variations do not affect the overall temp co of the composite resistance.

rg

[edited to clarify]

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« Last Edit: Jun 21^st, 2010, 9:00am by RobG »

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