REF REF 设RF=R2 R 2R 4R 8R RE d do i=10do+1a1+12d2+l3dl3 REF d+-d1+-d2+ REF 8R 4R 2R R =n5(432+a222+d12+an20 R R FF i=--A(d323+d22+a12+do2) 2 2R 2R 4R 8R RF I 1 I I 3 I 2 0 I REF i F i S3 S2 S1 S0 d3 d2 d1 d0 +VREF uo － + ( 2 2 2 2 ) 2 8 4 2 0 0 1 1 2 2 3 3 3 0 1 2 3 0 0 1 1 2 2 3 3 =  +  +  +  = + + + = + + + d d d d R V d R V d R V d R V d R V i I d I d I d I d REF REF REF REF REF ( 2 2 2 2 ) 2 2 0 0 1 1 2 2 3 o 4 3 = − = −  = − d  + d  + d  + d  V i R u R i REF F F 设RF=R/2