A mechanical frequency generator has a first mechanical resonator and a second mechanical resonator and a circuit connected with the first and second mechanical resonators. The first and second mechanical resonators having substantially the same resonator frequency coefficients as a function of an environment of the first and the second mechanical resonators. The first mechanical resonator differing in size from the second mechanical resonator. The circuit adapted to generate a difference frequency signal responsive to the first and second mechanical resonator frequency signals and based on the first and the second predetermined resonant frequencies.