Patent ID: 6993445

Claim:
A process variable transmitter, comprising: a first phase-locked loop having a first bandwidth producing a first output signal, and operable to lock into a frequency of an input signal; a second phase-locked loop having a second band width narrower than the first bandwidth, producing a second output signal, and operable to lock into the frequency of the input signal with greater accuracy and greater immunity to noise than the first phase-locked loop, wherein the second phase-locked loop includes a center frequency input, and the center frequency input is coupled to the first output signal to assist lock-in by the second phase-locked loop; and a switch operable to switch an output signal of the process variable transmitter between the first output signal and the second output signal in response to a change in the frequency, and based on at least one of a first lock indicator signal and a second lock indicator signal, wherein the first lock indicator signal indicates whether the first phase-locked loop is locked into the frequency and the second lock indicator signal indicates whether the second phase-locked loop is locked into the frequency.