A crystal oscillator with automatic amplitude control and digitally controlled pulling range of ±100 ppm

In this paper we report a digitally controlled crystal oscillator (DCXO) at 32.000 MHz. The circuit has an automatic control circuit to ensure that the voltage at the two crystal pins is always above ground, thereby avoiding waveform-clamping by ESD diodes. The stable amplitude keeps the power dissipation in the external crystal well controlled. The circuit also includes a digital tuning scheme to pull the crystal frequency by ±100 ppm around the center frequency with a 0.45 ppm/step resolution.