Apparatus and method to calibrate clock phase mismatches

Abstract

A digital phase spacing detector with programmable delay lines is described. Each programmable delay line receives a clock. The output of the programmable delay lines is compared by a logic and then passed through a glitch detector. Each of the clocks pass through the programmable delay lines that are tuned to a point where the clock edges at the output of the delay lines are aligned and glitches start appearing at the output of the logic. A calibration scheme uses replica cells (replica of VCO cells) in the measurement path. The calibration scheme calculates the average of clock phase differences through a digital control replica buffer, and this average clock phase difference is applied to the VCO delay stage cells. The PLL is then allowed to relock with the calibrated VCO delay stage cells. This process can be repeated several times to reduce the phase errors between the clock phases.