Patent ID: 7978017

Claim:
An apparatus to generate a harmonic reference signal, the apparatus comprising: a reference resonator configured to generate a first reference signal having a resonant frequency; a control voltage generator configured to provide a temperature-dependent control voltage, said control voltage generator comprising: a first current source configured to generate a temperature-dependent current; a variable resistance circuit coupled to the first current source, an amount of resistance of the variable resistance circuit selectable to determine a variation in the temperature-dependent current for a corresponding variation in temperature; and a plurality of variable reactance modules couplable to the reference resonator and couplable to the control voltage generator, each reactance module of the plurality of variable reactance modules configured to modify a corresponding reactance in response to the control voltage to maintain the resonant frequency within a predetermined variance over a predetermined temperature range; wherein the variable resistance circuit comprises: a plurality of resistors, each resistor of the plurality of resistors having a fixed resistance; a plurality of switches correspondingly coupled to the plurality of resistors, each switch of the plurality of switches responsive to a control coefficient to couple or uncouple a corresponding resistor of the plurality of resistors to provide the variable resistance; and a plurality of current mirrors or current sources correspondingly couplable through the plurality of switches to the plurality of resistors.