Education Library

Frequently Asked Question

How do I determine if a VCO is good enough for my purpose?

The VCO which I'm considering doesn't have a phase noise graph in its data sheet.

Determining the phase noise performance of a VCO or VCXO can be difficult. If possible, try to get a plot or set of plots of phase noise for the VCO/VCXO from the manufacturer. If this information is not in the product data sheet, you will have to contact the vendor application support to request this.

Alternatively, if you have access to a phase noise measurement system, such as the Agilent E5500, you can make the phase noise plots yourself. This is a pretty involved process, though.

A growing number of available VCOs and VCXOs from the leading vendors have been characterized and included in the library of ADIsimCLK. Check there to see if your VCO/VCXO has been included. If it hasn't yet been included, let Apps Support know so that we can put it on our list for future inclusion in the library.

When the phase noise values for your VCO/VCXO are known, use ADIsimCLK to simulate the jitter performance of the ADI clock distribution IC using that component. For VCO/VCXO parts which are not yet included in the ADIsimCLK library, the phase noise can be manually entered in the appropriate spot in the program's user interface, and the simulations continued. The effect of various amounts of VCO/VCXO phase noise can easily be seen and appreciated in the results given by ADIsimCLK. This will help you to determine a suitable candidate for your VCO/VCXO.