A frequency steered phase-locked loop

Abstract

Narrow bandwidth phase-locked loops (PLLs) can have difficulty acquiring lock reliably when there is a significant difference between the input signal and the free run frequency of the PLL's voltage-controlled oscillator (VCO). The new technique presented here incorporates an accurate local reference frequency into the PLL structure. The range of frequencies to which the new PLL structure can lock can be confined to a desired small region around the accurate local reference frequency. The new PLL structure also provides other benefits such as reduction of VCO phase noise. The new technique does not require any monitoring nor any switching of the local frequency reference signal which is always acting. The key parameters of the new PLL structure are identified and the performance characterized.