Patent ID: 7200092

Claim:
A method for adjusting a reference level of an analog signal from a plurality of periodically sampled points, said method comprising steps of: comparing a first number of sampled points having levels higher than an initial reference level with a second number of sampled points having levels lower than said initial reference level within a specified period; raising said initial reference level when said first number is greater than said second number, and lowering said initial reference level when said first number is less than said second number, thereby obtaining a new reference level, and defining said new reference level as a first-stage reference level; determining a first level shift from said first-stage reference level to a last second sampled point within said specified period and a second level shift from said first-stage reference level to a last sampled point within said specified period when one of a first level of said last second sampled point and a second level of said last sampled point is higher than said first-stage reference level and the other is lower than said first-stage reference level; and moving said first-stage reference level toward said first level when an absolute value of said first level shift is greater than an absolute value of said second level shift, and moving said first-stage reference level toward said second level when said absolute value of said first level shift is less than said absolute value of said second level shift, thereby defining a second-stage reference level.