请教一个关于BG温度曲线的问题,谢谢!

USTM

拉扎维那本书上到是提到这个曲线是由于Vbe,Ic,还有Vos随温度变化引起的,但没有具体解释,艾伦的到是讲得多,但不够直观,请问老兄看的是什么书啊?
外加我同事做的基准和我的结构不同,但结果一样.起先他的也是左边的图,但PPM太高,调整后PPM下降,但却又成右边那个图了.这个是不是和模型参数也很有关系啊?非常感谢,希望各位指点!

syracuse

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robberxiong

我不知道你们公司用的是那个foundry厂的库，我是没有遇到这种情况的，我们
做的带隙参考源仿真都是左边那种图形，当然我们公司用的是XFAB的工艺，那个
非常好。不过一般来讲，foudnry厂给的都是一阶温度系数模型参数，我上次写的
那个公式也是一阶公式近似，对于仿真足够说明问题。

kmlabc

我仿真用的是SMIC0.35UM工艺
最近看了一下其他的论坛，关于bandgap这方面的问题也有被讨论
下面摘录一些，大家看看，可能会有启发

05 Nov 2007 13:17   why my bandgap voltage looks like below?     
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why my bandgap voltage looks like below?
i think it should be lke a parabola and will be change with different resistance values
i have checked all the transistors in the saturation region
in the design above,the ratio of pnp transistor i used is 2:1
however, when i changed the ratio of pnp transistor from 2:1 to 8:1 and modify the resistance value accordingly, i got another pic which is a parabola . what surprised me is the voltage fluctuation with the temperature of the two design is equal, that is 3mv, but why ? anyone can help me ? thx in advance



05 Nov 2007 15:05   Re: why my bandgap voltage looks like below?   
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you can upload your schematic.Maybe you have a curvature compensation.it's a wonderful result!



06 Nov 2007 8:13   why my bandgap voltage looks like below?   
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Generally, this results is good. But this results can be related with factors that can lead to bad behavioural during another kind of simulation. E.g. to be sure u should check how ur circuit sensitive to supply variation.

P.S. Ratio 2:1 too small I think. The lager ration can helps you to eliminate influence of error amplifie offset.
Report msg +5pts



07 Nov 2007 3:00   Re: why my bandgap voltage looks like below?   
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DenisMark wrote:
Generally, this results is good. But this results can be related with factors that can lead to bad behavioural during another kind of simulation. E.g. to be sure u should check how ur circuit sensitive to supply variation.

P.S. Ratio 2:1 too small I think. The lager ration can helps you to eliminate influence of error amplifie offset.



i have checked the influence of supply variation to my bandgap voltage. it is good since i used folded cascode in OTA.
just like u said,2:1 is too small,a larger ratio should be better. however ,i am puzzled by the different curve with differnet pnp ratio (of course , resistance value also modified to obtain the smallest variation against temperature)



07 Nov 2007 5:07   Re: why my bandgap voltage looks like below?   
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Your result shows it have a good performance and it have 2nd order curvature compensation. Keep the design, it should not be a problem.
If you do not design for 2nd order compensation , I have two questions to ask:
Do you use the same type of resistor for all the resistors in the bandgap?
Do you add a resistor at the base of the bipolar transistor?



07 Nov 2007 6:52   Re: why my bandgap voltage looks like below?   
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WindRay wrote:
Your result shows it have a good performance and it have 2nd order curvature compensation. Keep the design, it should not be a problem.

If you do not design for 2nd order compensation , I have two questions to ask:
Do you use the same type of resistor for all the resistors in the bandgap?
Do you add a resistor at the base of the bipolar transistor?

resistors i used in the bandgap are of the same kind, that is nwell resistor
and i did not add resistor at the base of the bipolar transistor
Report msg +5pts



07 Nov 2007 9:37   why my bandgap voltage looks like below?   
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Have you read this post http://www.edaboard.com/ftopic278530.html?
What ratio of resistor do u have? What expected offset of amplifier? Is results after Monte-Carlo simulation acceptable for you?

Obtained result related with operation region of bipolar transistors. U can try to achieve same operation for another retio. May be it possible.
Report msg +5pts



07 Nov 2007 9:46   Re: why my bandgap voltage looks like below?   
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Hi, I can see you almost have 1.19 V & the variation is too small so < I can say it's accepted
best regards,
Rania
Report msg +5pts



08 Nov 2007 2:56   Re: why my bandgap voltage looks like below?   
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DenisMark wrote:
Have you read this post http://www.edaboard.com/ftopic278530.html?
What ratio of resistor do u have? What expected offset of amplifier? Is results after Monte-Carlo simulation acceptable for you?

Obtained result related with operation region of bipolar transistors. U can try to achieve same operation for another retio. May be it possible.


The post you suggested is very helpful. I havenot considered the effect of resistor's ratio to offset voltage. I just ran simulation in all corners and did not run Monte-Carlo simulation .
BTW:Is it necessary to run post simulation? i think i should,but many people say that is no necessary

thx a lot  



08 Nov 2007 3:45   Re: why my bandgap voltage looks like below?   
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One fast way to check the effect of the Bandgap opamp without running MC analysis is to insert a dc offset voltage at the input of the opamp. That will be able to see the effect of bandgap due to offset.

This is normally done if you donot have MC analysis in your EDA tools or the process does not support MC analysis as the process need to define amount of mismatch between devices.

Added after 18 minutes:

hi lxcpku

After thinking for so long on your temperature curve, I still does not understand how come if you design a first order bandgap, you can get a 2nd order bandgap. I guess it will be good if you can understand what is the reason and share with us.

In my years of design, I have see only 1 order bandgap behaves as 1st order (parabolic) except they have problem when the temperature is higher than 120degrees, the curve start to increase very fast. The reason I guess is at high temperature, the models may not be so well modelled. It is not the case in measurement.

Please share your finding if you have any.. Thanks.



08 Nov 2007 11:02   why my bandgap voltage looks like below?   
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Hi, lcxpku, your BGR really looks so strange, I havn't ever seen this kind of bang-gap curve. Most of the curves raise from -40~40, and falls from 40~100, 2nd-order BGR would raise a little from 120~150.
I have ever designed a BGR with a 1st structure, in simulation it behaves like a 2nd-order one, but in test it is just a 1st one. It caused by the un-well modeled resistor, BJT, etc. a 10mV Vptat may impact greatly by the OTA off voltage.
Would you share your schematic with us?

kmlabc

楼主的问题解决了没
说说进展阿

xiongshoufen

这2个图我都见过的，应该都可以tapeout了，但是什么因素导致的，我不太清楚的。

122013137

个人觉得无所谓哪条曲线，关键是符合不符合你的要求

USTM

非常感谢各位的回答,因为我也是第一次做,而且明年2月要到代工厂去做MPW,经验不足,而且又秉承多问问,莫太迷信仿真结果的思维,所以才这么谨慎的.
我个人觉得两种曲线可能是由于PNP的模型参数问题,导致Vbe的温度参数不同.我原来用的是上华0.5的模型,现在换成0.6的模型了,这个问题就没有存在了,图形又变成了左图.而且个人发现,06模型中,PNP5  PNP10  PNP20所产生温度曲线差距很大,其中PNP10的最好Vref=1.25V,而PNP20的其次Vref=1.29V,PNP5最差,Vref=1.32V.请问通常是不是越接近1.25V,其温度特性就越好.

wap1000

我现在也在设计BGR，也发现管子从pnp5换做pnp10，TC能达到更好的数值。看到有关的文献最后得出的vref都是1.2伏左右，但没有细节标注究竟1.2伏多少TC 是最好，这个要具体调节电阻参数吧。

forestm

robberxiong,你说的很详细！