各级串联电阻的计算公式为: x1=(B-1)Ra R2=(-1)Ba=BR1 Rst3=B-dB-Ra= BRst2 Rstm =(B-DBmRa= Brstm-I各级串联电阻的计算公式为： 1 1 2 2 3 2 1 1 ( 1) ( 1) ( 1) ( 1) − − = − =  = − = = − = = − a stm m stm st a st st a st st a R R R R R R R R R R R          