A 2.1-MHz crystal oscillator time base with a current consumption under 500 nA

A micropower crystal oscillator module for watch applications is presented. The integrated circuit is encapsulated with a 2.1-MHz crystal in a miniature vacuum package to reduce parasitic effects. The circuit comprises frequency tuning with a resolution of +/-3 s/year [+/-0.1 parts per million (ppm)] and auxiliary circuits. A single output delivers a signal of 16 384 Hz with a frequency stability of +/-2 ppm over the temperature range (-10 to 70 degrees C). The oscillator core has two complementary active MOSFET's and amplitude stabilization in order to get both low power consumption and high stability. New coupling and biasing circuits between the oscillator and the dynamic frequency dividers allow to achieve a current consumption under 0.5 mu A for a supply voltage between 1.8 and 3.5 V.