Abstract: A clock reference includes a substrate, a first resonator and a second resonator both formed on the substrate providing a differential resonator pair. A first variable capacitor is connected across electrodes of the first resonator for electronically tuning a first native frequency of the first resonator to provide a first tuned frequency (f1) and a second variable capacitor is connected across electrodes of the second resonator for electronically tuning a second native frequency of the second resonator to provide a second tuned frequency (f2). A frequency mixer is coupled to receive f1 and f2 for generating a frequency difference signal.