An inductive-coupling link has been studied for inter-chip communications in System-in-a-Package . Its communication distance extends millimeter ranges [2,3] and it can be used as a wireless interface for non-contact memory cards. High speed and low power communication can be performed in the inductive-coupling link because of the removal of highly capacitive ESD protection devices . The wireless interface eliminates mechanical contacts resulting in high reliability. Target data rate is 2.5Gb/s/ch which is 12.5x higher than that of a commercial memory card and target communication range is 0.5mm to 1mm, considering the allowance of card insertion. The maximum data rate of the inductive-coupling link demonstrated in  at 1mm distance was 160Mb/s/ch. A theoretical limit is 1Gb/s/ch since self resonant frequency of an on-chip inductor of 3GHz. To increase the self resonant frequency, the inductor is moved off chip to a flexible circuit board to reduce parasitic capacitance. The self resonant frequency of 1mm diameter inductor is increased to 4GHz corresponding to a signal data rate of 1.25Gb/s/ch. Additionally, the number of bit per symbol is increased to 2 by 4 pulse amplitude modulation (4PAM) and a data rate of 2.5Gb/s/ch is achieved. But to communicate by using 4PAM in the inductive-coupling link, issues listed below must be solved. First, the communication range is limited to 0.95mm to 1mm. The amplitude of the received signal is inversely proportional to the communication distance, and therefore, received signal cannot be converted to a correct data without adjusting the input threshold voltages of a receiver. Second, the pulse width is narrower in 4PAM and thus synchronization on the receiver side is difficult.