Phased locked loop with multiple voltage controlled oscillators

摘要

A phased locked loop (PLL) incorporates multiple voltage controlled oscillators including one that operates in a lower frequency range than an operational VCO used by the PLL. A VCO selection circuit allows the system to select from one or more alternate VCOs. A ring oscillator VCO may be used as the alternate VCO for a PLL that uses a LC VCO for the operational VCO. While the ring oscillator VCO provides lower performance, the ring oscillator VCO allows the system with the PLL to be run at a lower speed for testing, debugging or characterization.

主权项

1. An electronic circuit comprising:
a phased locked loop with a plurality of voltage controlled oscillators that each provides a variable high frequency signal required for the phased locked loop; a first voltage controlled oscillator of the plurality of voltage controlled oscillators; a second voltage controlled oscillator of the plurality of voltage controlled oscillators that is of a different type than the first voltage controlled oscillator and provides a frequency lower than the first voltage controlled oscillator with a greater frequency range than the first voltage controlled oscillator; a multiplexor that inputs an output from each of the first and second voltage controlled oscillators and provides an output frequency for the phased locked loop; and select logic connected to the multiplexor that selects whether the multiplexor uses the output from the first voltage controlled oscillator or the output from the second voltage controlled oscillator for the phased locked loop.