A Spur Suppression Technique Using an Edge-Interpolator for a Charge-Pump PLL

Abstract

This paper proposes a new reference-spur elimination architecture for a charge-pump-based phase locked loop (PLL) using an edge interpolation technique. By utilizing a charge-distribution mechanism on the control voltage of the voltage-controlled oscillator, the proposed architecture is capable of suppressing high-order harmonics of the reference spur, as well as a fundamental spur. In implementation, the eight-stage edge interpolator achieved more than 16-dB additional spur suppression. In addition, the harmonics of the reference spur within a 104-MHz frequency offset, the location of the eighth harmonic of the reference spur, were dramatically suppressed. The prototype PLL was fully integrated in a 0.18-mu m CMOS technology, which occupies a 670 mu m x 640 mu m active chip area. Additional circuits for the edge interpolator consumes less than one-fifth of the total area and power.