標題: 一個SAR adc的問題 [打印本頁] 作者: josephlll 時間: 2009-2-10 10:15 PM 標題: 一個SAR adc的問題 各位好: # \* a% ^* E7 O% z1 l我有一個sar adc 12bit 200ks/s的問題0 I$ r4 v5 ]. _ I8 b7 s7 d
1.為了要有12bit的解析度，所以sar adc中的comparator的gain 需要 * W9 B! @0 y- m2 ?' t 20*log4096=72db，且為了要有200ks/s的sample rate，所以clock得為 5 W- C5 d$ A3 L1 S0 T3 @# d 12*200ks/s=2.4Ms/s。現在有個問題就是，comparator如果用 opamp做，有沒有 * F- r4 t# M4 x4 j% h3 I 那種在frequency=2.4M下，gain=72db的電路? 7 n# Y2 S L! O, n# k2.也就是說unity gain bandwidth product=4000*2.4M=9.6G，請問這有沒有算錯? 0 E7 T8 O. |: q+ e. b3.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) O8 t: f, r! L+ t/ N& C8 I ，那是不是只能用comparator latch的方法? 7 B' Z/ I6 W5 P9 i, [ & C( }' k2 Z2 X: t如果有說錯，請提出，謝謝作者: yourkey 時間: 2010-3-18 01:26 PM
應該用dynamic comparator就可以達到high speed的功能了 當然前面要加各preamp.作者: brandon1023 時間: 2010-3-24 05:37 PM
請問為什麼要用opamp來取代comparator? 1 |6 y8 b8 j: E, m8 O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？2 L, Q% {* ?" [7 X' m1 a/ v
一般情況建議還是使用comparator作者: qw101 時間: 2010-3-24 11:37 PM
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‧作者: zhuleiyacht 時間: 2010-3-29 03:00 PM
比较器肯定要用高速高精度比较器，需要多级。作者: iamif520 時間: 2010-4-2 07:49 PM
看了各位的回答覺得有所收穫。 0 i! u3 q1 M0 o$ ?% S* Q請問有哪些典範可供參考? (可列書名或論文名)作者: jameson2 時間: 2012-2-1 03:17 PM
恩 幾乎SAR看到的comparator都是dynamic的型態，動作速度快!!作者: finster 時間: 2012-2-12 08:03 AM
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* E5 w+ a& J4 \5 a! O- o& S/ X
若以sar adc而言,尚不需要用到op amp,用dynamic comparator應就足以勝任了作者: anita66 時間: 2012-2-16 03:45 PM
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~作者: arsenal_he 時間: 2012-3-22 03:48 AM
What u need is high resolution to resolve tiny difference at input and high speed to accommodate to the sampling rate. 6 ~" y2 y2 ?% m( zSo 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. " |5 Q0 J4 R }. ~" \7 N: pAnd you may need several stages of preamplifiers with high bandwidth ones for initial stages.作者: arsenal_he 時間: 2012-3-22 03:48 AM
What u need is high resolution to resolve tiny difference at input and high speed to accommodate to the sampling rate. - s% M: p/ P0 J$ O" e) w3 Z9 rSo 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. 6 h& p' u7 k7 x
And you may need several stages of preamplifiers with high bandwidth ones for initial stages.