Education Library

Frequently Asked Question

How do I use a DDS for a clock driver?

To use a DDS as a clock driver, the output sinewave must be converted to a rectangular wave with fast edge transitions (high slew rate). In order to do this, it is necessary to pass the AC output signal through a high-speed comparator, with an output of the correct voltage level.

Many of the ADI DDSs have integrated high-speed comparators in order to make clock signal generation simple. It is also always possible to use an external, high-performance, high-speed comparator from ADI. But, in all cases – don't forget the low pass (band pass) filter.

Please refer to Application Notes AN-823, "Direct Digital Synthesizers in Clocking Applications" and AN-837, "DDS-Based Clock Jitter Performance vs. DAC Reconstruction Filter Performance" for more detailed information.