12bit sar adc 500kps

mikeppq

打算做一个12bit 500kps sar adc，采用三分段电容结构，全差分静态比较器。
想问一下，这样能否达到500kps现在的要求？或者说还是要采用电容电阻复合结构？
请高手指点一下，谢谢！

mikeppq

自顶一下，有知道的请指点一下，谢谢了。

ducvilla

For the comparator: you should choose fully dynamic structure.

About the DAC: it's better if you use CDAC not integrate CDAC + RDAC.

There are a reference paper might be good for your selection:
"An Energy-Effi cient Time-Domain Asynchronous 2 b/Step SAR ADC With a Hybrid R-2R/C-3C
DAC Structure" - JSSC 2014.

ducvilla

You should design SAR ADC with total dynamic comparator not static one to avoid large power consumption.

About using the CDAC or CDAC + RDAC, with 500 kS/s, I recommend you use CDAC.
This paper might be good reference for your selection:
"An Energy-Efficient Time-Domain Asynchronous 2 b/Step SAR ADC With a Hybrid R-2R/C-3C
DAC Structure" - JSSC 2014.

lishiliang

顶一下。。。。。

打算用什么工艺？ SAR ADC做12bit是不是比较难？ 需要加校正吗？
500Ksps好像不是很高，就是做12bit精度比较难。。。。。。

希望LZ多多交流，请前辈多多指教。。。

semico_ljj

速度不高

semico_ljj

回复 4# ducvilla

能提供论文吧？

mikeppq

回复 4# ducvilla


    谢谢！
我现在用的是三段式的CDAC，但在段与段之间跳变的时候总是有误差。
全动态比较器能否达到12bit？
我现在用的是静态比较器。有资料上说是10bit以下动态比较器，12bit以上是静态比较器，不知这个说法有没有根据？

mikeppq

回复 5# lishiliang


   谢谢。
用的是IBM 0.18um工艺
正在想校正的事情，不加校正好像不行。

ducvilla

Hi mikeppq,

No one use static comparator for SAR ADC, because in SAR ADC, comparator involve in a lot of circles of switching, so static comparator can not meet the specification. To check this thing, you just design a static comparator with clock frequency (comp) = fs(SAR) * 12 (I assumed you design asynchronous SAR ADC), and probe the average power consumption.

Your ADC is design in 0.18 um, it's possible that supply voltage = 1.8v, so there are a lot types of dynamic comparator can stand for 12bit with this supply.

When you use 3 stages of CDAC, it means you will use split capacitor, right? if it's the case, the  problem is how you can do the layout for the bridge capacitor (example, Cb = 17/16 * Cunit).

The last thing is, if your design is for research, it's rare to see any papers had specification: 12b + sampling rate ~ 500kS/s. Normally, for biomedical devices: the res = 8-10b with sampling rate = 100k - 1M, and for wireless sensor network: res = 10-12b, fs = 1M-10M.