Apple Inc.
Duty cycle and skew measurement and correction for differential and single-ended clock signals

Abstract:

A system and method for efficient on-chip monitoring of clock signals post-silicon. An electronic circuit includes a post-silicon and on-die signal monitor and a first signal generator that sends a first signal with a first signal period to the signal monitor. The signal monitor selects a first sampling signal with a first sampling period such that a ratio of the first sampling period to the first signal period is greater than one and is a non-integer. The signal monitor selects a reference voltage level for indicating when the first signal is asserted. When the first sampling period has elapsed, the signal monitor samples the first signal to generate a voltage level, and upon completing sampling, determines a duty cycle of the generated voltage levels, which indicates a duty cycle of the first signal. Using a similar approach, the signal monitor is also capable of determining skew between two signals.