As the demand of data transmission bandwidth is increased, the issue of impedance matching becomes important factor for the high-speed serial link transceiver. Especially, there are many standards of the characteristic impedance in today's transmission media. We propose a digital approach of on-die adaptive termination resistors in the transceiver. It can match the characteristic impedance of coaxial cable automatically from 75 Ω ∼45 Ω without any external component and bias. Using tsmc 0.18 um CMOS process, the tuning process can be finished in 14 clock cycles and the difference between termination resistor and coaxial cable is less than 5Ω for the range of characteristic impedance from 75 Ω to 45 Ω.