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godspeed.w
Joined: 15 Mar 2006
Posts: 39
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 22 Oct 2009 8:01 about bandgap design |
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| I found that the temperature coefficient of my technology is so big(tnf1=1.4e-4) and I can not design a 20 ppm bandgap for my circuit.who have idea about low ppm bandgap .
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penghan
Joined: 20 Sep 2004
Posts: 72
Helped: 2
Location: Shanghai
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22 Oct 2009 8:27 about bandgap design |
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You had better paste your schematic here.
Bandgap with a TC lower than 20ppm is not a diffcult work.
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tzg6sa
Joined: 03 Jun 2008
Posts: 12
Location: Hungary
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22 Oct 2009 14:04 Re: about bandgap design |
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| In which temperature range? The smaller the temperature range the smaller the tempco is.
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22 Oct 2009 14:04 Ads |
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godspeed.w
Joined: 15 Mar 2006
Posts: 39
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22 Oct 2009 14:56 Re: about bandgap design |
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| from -40 to 85 the output voltage have 10mv variation.
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dick_freebird
Joined: 04 Mar 2008
Posts: 312
Helped: 45
Location: USA
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23 Oct 2009 19:16 about bandgap design |
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That kind of tempco may not be attainable without some
curvature correction, and c.c. is a first class bitch to get
right (cubic response magnifies all the "make" tolerances
even worse than the parabolic plain bandgap).
The ultra-precision, ultra-stable ones all seem to be using
a temperature sensor, digitized, and a compensation map
in ROM/EEPROM to get an arbitrary dead-nuts correction.
10mV may be on the edge of doable, but I would expect
the model accuracy alone to be a significant issue with
little hope of resolving it beforehand. You might find you
have to take your own diode and resistor data and fit
your own, possibly veriloga models (simple tc1, tc2 may
not suffice). This usually takes an initial pass with the
best guess bandgap plus key elements to extract better
models from, and a tweak pass through fab.
Unless you're a genius at guessing and have great karma.
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godspeed.w
Joined: 15 Mar 2006
Posts: 39
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25 Oct 2009 2:09 about bandgap design |
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| I agree that curvature correction should be used in this technology(tnf1=1.4e-4,tnf2=1e-6).and I do my best to design a low ppm bandgap .
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leehying
Joined: 02 Aug 2008
Posts: 38
Helped: 2
Location: China
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25 Oct 2009 7:45 about bandgap design |
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where do tnf1=1.4e-4,tnf2=1e-6 come from?
My problem is trimming to lower tempco, since trimming is performed at room temper only.
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jesseyu1984918
Joined: 16 Jun 2008
Posts: 13
Helped: 1
Location: Singapore
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02 Nov 2009 10:18 temprature stability of bandgap design |
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| The TC alone doesn't affect your final TC since it's Vbe +deltaVbe, even though the TC for BJT is big, it doesn't necessarily means the bandgap can't be designed, usually the accuracy is mainly affected by 3-sigma variation of the device rather than the TC of the device.
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godspeed.w
Joined: 15 Mar 2006
Posts: 39
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12 Nov 2009 15:05 Re: temprature stability of bandgap design |
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I found that if I delete parameter of tc2 in my .lib file I can realize 20ppm.
so I think that tc2 is the main reason.
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dick_freebird
Joined: 04 Mar 2008
Posts: 312
Helped: 45
Location: USA
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12 Nov 2009 16:40 temprature stability of bandgap design |
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You have to ask yourself whether you are improving the result
in simulation-space by removing realism. I suspect this is
the case.
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