Circuit for optimizing a delay line used to de-skew received data signals relative to a received clock signal

Abstract

Delay circuits have programmable delay elements to delay data signals so a clock samples the data signals in the middle of the eye window pattern. The clock is frequency divided by two, generating a divided clock coupled to a clock delay circuit and a data delay circuit generating a toggle clock and a delayed toggle clock that are sampled with the clock signal. A state machine varies the number N of delay elements selected in the data delay circuit until successive samples of the toggle clock and the delay toggle clock have opposite logic stages. The resulting number N is the number of delay elements required to generate a delay equal to one period of the clock. The delay of each delay element is adjusted using adjustment control signals until an N is generated that is within a predetermined range. The adjustment control signals are distributed to the data delay circuits.