Patent ID: 7697649

Claim:
A circuit for measuring an eye size comprising: a sampler configured to generate first sampled data by sampling received data based upon at least one shifted clock signal, the at least one shifted clock signal being obtained by shifting each phase of at least one of recovered clock signals by respectively predetermined phases, the recovered clock signals having phases different from each other and being recovered from the received data in response to a digital code; an error counter configured to generate an error count for calculating the eye size of the received data by comparing the first sampled data with second sampled data, the second sampled data being obtained by sampling the received data based upon the at least one of the recovered clock signals; and a shifted clock signal generator configured to sequentially shift the digital code to generate a shifted digital code and configured to generate the at least one shifted clock signal in response to the shifted digital code, wherein each value of the error count is obtained by summing the comparison result of the first sampled data and the second sampled data with respect to each value of the shifted digital code.