The behavior of the crystal oscillator has an effect on the accuracy of the PLL and its ability to meet stringent Telcordia and ITU-T requirements. Three (3) types of oscillators can be used with IDT's WAN-PLLs. The oscillators typically differ in how they maintain their output frequency over a range of ambient temperature.
1. OCXO (oven compensated crystal oscillator)
2. TCXO (temperature compensated crystal oscillator)
3. XO (uncompensated crystal oscillator)
A TCXO is more sensitive to changes in ambient temperature conditions than an OCXO. In the case of a TCXO, electrical temperature compensation seeks to offset the effect of a temperature change on the crystal. The OCXO attempts to maintain a constant temperature environment around the crystal using a heater, to a level that is higher than the maximum rated external ambient temperature (typically 85°C). Refer to application note AN-807 for more details. For other questions not addressed by the Knowledge Base, please submit a techical support request.