REF REF 设R=R/2 R 2R 8R RE i=Iodo+Id,+l2d2+lsd REF REF d,+ ke d2+ Fd 8R 4R 2R R =R(d323+d22+ad1·2+dl0·2 23R R R FF 3(d2…2+d,22+a12+dn·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