cd74hc4053 on-state resistance is 70 ohm.thanks for replying.i just find from relesed note that cd74hc4053 on-state resistance is 70 ohm.maybe it has been improved than those in 2001.max multiplexer and swithch chip family does have better one like max4677 with ron=1.6ohm,but it's much more expensive that 4053.thank you again for your tips!