Clock, frequency reference, and other reference signal generator with frequency stability over temperature variation

Exemplary embodiments provide a reference signal generator having a reference or center frequency within a predetermined variance over variations in temperature within a specified range. An exemplary apparatus comprises a reference resonator to generate a first reference signal having a resonant frequency, with the reference resonator having a first temperature dependence; and a plurality of switchable circuits, with at least one switchable circuit providing a second temperature dependence opposing the first temperature dependence to maintain the resonant frequency within a predetermined variance over a temperature variation. A wide variety of switchable circuits are disclosed, including a transistor having an on resistance value greater than a nominal resistance, a resistor coupled to a transistor or other switch, and circuit comprising a first reactance coupled to a first switch, with a second reactance coupled to a resistance and a second switch coupled in series to the second reactance or to the resistance. Various coatings may also be applied to an integrated circuit embodiment, such as a silicone coating on a first surface and a metal layer on a second surface.