On-chip measurement of signal state duration

Abstract

A signal duration measurement system compares a known duration, Tof a test data signal with the duration, Tof a state of a signal under test. In one embodiment, if Tcompares favorably with Tthen the circuit generating the signal under test 'passes.' Otherwise the signal under test 'fails,' and a problem has been identified. Furthermore, in one embodiment, Tcan be selectively adjusted to more accurately measure TIn one embodiment, the test data signal is allowed to travel a signal path, having a known signal propagation delay time, during a single state of the signal under test. The data signal at the beginning of the state, e.g. during the rise of the signal under test, is compared to the data signal captured at the end of the state, e.g. during the fall of the signal under test. If the initial and captured data signals are the same, then the duration of the state of the signal under test is greater than or equal to the signal propagation delay time. The signal propagation time can be adjusted by inserting varying delay elements into the signal path traversed by test data signal. The signal duration measurement system can be fabricated on-chip, thus making its use more practical. The signal duration measurement system is, for example, useful for measuring the state duration of signals such as self-resetting signals, which are difficult to externally measure.