Method and apparatus for reducing jitter and improving testability of an oscillator

摘要: An oscillator such as a pulled-crystal (50) provides low clock jitter by converting sinusoidal voltage on crystal's (51) terminals into digital square wave with comparator (56). The oscillating frequency of the crystal is pulled selectively switching in extra capacitance through capacitor digital-to-analog converters (CDACs) (57, 58). has built-in testability which allows individual capacitors CDACs 58) to be quickly tested for opens. A scan path connected inputs selecting capacitors. first input terminal (56) precharged before under test (171) connected. comparison provided second terminal. determined functional if, after being (56), it discharges below voltage, causing switch.