一個SAR adc的問題

josephlll

各位好:
8 w1 t, o# u% L; ?: N/ a/ `0 ]/ @我有一個sar adc 12bit 200ks/s的問題
) D8 v4 A4 }& ~( A6 `1.為了要有12bit的解析度，所以sar adc中的comparator的gain 需要
   20*log4096=72db，且為了要有200ks/s的sample rate，所以clock得為  
5 Z# j: E2 L, a: F" n! G2 R  12*200ks/s=2.4Ms/s。現在有個問題就是，comparator如果用  opamp做，有沒有
$ w8 k, ?3 O5 j, ^6 p3 N! v  那種在frequency=2.4M下，gain=72db的電路?
7 X# t) w! k7 L& }( W& h4 M2.也就是說unity gain bandwidth product=4000*2.4M=9.6G，請問這有沒有算錯?
; x# d) d3 o8 B0 D3.如果沒有(查過論文folded telescopic opa好像最大只有40db左右，可能有沒查到)
  ，那是不是只能用comparator latch的方法?
1 m2 z/ u% V" y$ H1 r7 g
! R4 a: `  g" w3 n$ h/ u如果有說錯，請提出，謝謝

yourkey

應該用dynamic comparator就可以達到high speed的功能了  當然前面要加各preamp.

brandon1023

請問為什麼要用opamp來取代comparator?
* @8 g4 U9 ?" ^9 P* K單純做一個high gain, high speed的comparator應該不是太難。但是換成opamp就難多了吧？
一般情況建議還是使用comparator

qw101

個人覺得gain and unity gain bandwidth 推導有點問題，一般而言要做high resolution, high speed不會用單一opamp or comparator‧

zhuleiyacht

比较器肯定要用高速高精度比较器，需要多级。

iamif520

看了各位的回答覺得有所收穫。
- c( y" e& a) v$ e8 {& c請問有哪些典範可供參考? (可列書名或論文名)

jameson2

恩 幾乎SAR看到的comparator都是dynamic的型態，動作速度快!!

finster

若是採用op amp,那你還需要作頻率補償,較難達到high speed,而且面積也較大
若以sar adc而言,尚不需要用到op amp,用dynamic comparator應就足以勝任了

anita66

多級串接+dynamic type. 但要注意比較器歸零的問題,通常可用muli-phase-clock的方式來解決,以上,個人淺見,請指教,3Q~

arsenal_he

What u need is high resolution to resolve tiny difference at input and high speed to accommodate to the sampling rate.
3 B1 y" I& E2 u) PSo you need to use comparator making of preamplifiers+latch. Preamplifier has negative exponential response and can amplify the small delta_vin to bigger output which will be developed to Voh thanks to the positive exponential response of the latch.
4 y" d9 S7 Y. i! f- f4 v' U9 r2 }And you may need several stages of preamplifiers with high bandwidth ones for initial stages.

arsenal_he

What u need is high resolution to resolve tiny difference at input and high speed to accommodate to the sampling rate.
So you need to use comparator making of preamplifiers+latch. Preamplifier has negative exponential response and can amplify the small delta_vin to bigger output which will be developed to Voh thanks to the positive exponential response of the latch.
And you may need several stages of preamplifiers with high bandwidth ones for initial stages.