Stable scalable digital frequency reference

A method for implementing a scalable stable digital frequency reference using a plurality of independent clock source circuitry, the method comprising the steps of:

• (a) for each of the plurality of independent clock source circuitry, providing a clock signal from an independent clock source as a first input into a direct digital synthesizer;
• (b) setting an initial phase and phase increment clock source cycle for each direct digital synthesizer during initialization to align the direct digital synthesizers in phase and frequency;
• (c) sampling an output phase of each direct digital synthesizer into a common synchronous clock domain;
• (d) generating a precision digital complex tone for each direct digital synthesizer;
• (e) adding the precision digital complex tone in-phase to other precision digital complex tones for each of the other direct digital synthesizer to generate a collective coherent vector sum;
• (f) providing the collective coherent vector sum as a feedback input into each phase and frequency measurement block of the plurality of independent clock source circuitry;
• and
• (g) conditioning the collective coherent vector sum and outputting a scalable stable digital frequency reference clock.