本文提出一种支持阻抗匹配功能的IO设计方法，该IO支持多电平标准；设计了一种易于实现的自动阻抗匹配模块。该模块主要设计思路是：首先通过比较用户提供的外部标称电阻和模块内部IO 镜像BUF阻抗，在经过一定周期的BUF阻抗调整后，使得内部BUF阻抗能匹配用户提供的标称阻抗，从而实现IO 多电压标准驱动能力和自动阻抗匹配功能。仿真结果表明，该电路可以工作在100MHz频率以上，快速实现自动阻抗匹配。

An IO design method supporting impedance matching is proposed in this paper. The IO supports multi-level standard.An automatic impedance matching module which is easy to implement is designed. Firstly, it compares the nominal resistance provided by users with the internal IO BUF impedance. After the impedance adjustment in a certain period, the internal BUF impedance can match with the nominal impedance provided by users, so as to realize the function of multi-voltage driving and automatic impedance matching. The simulation results show that the circuit can work above the frequency of 100MHz, and rapidly implement the automatic impedance matching.