APPARATUS AND METHOD FOR MINIMIZING TURN-ON TIME FOR A CRYSTAL OSCILLATOR

摘要

A temperature compensated crystal oscillator with an improved phase noise characteristic and a fast start up time includes a large time constant low-pass filter coupled to a temperature compensation circuit (14). At start up the low pass filter is effectively bypassed to enable the temperature compensation voltage and oscillator output frequency to settle quickly. A capacitance (C1) in the low-pass filter is precharged by a precharge circuit (24) to match the temperature compensation voltage without disturbing the temperature compensation circuit (14) and the concurrent settling of the oscillator (12). When the capacitance (C1) is fully charged, the low-pass filter is enabled without unsettling the oscillator output frequency (18).