Failure To Lock: Why Wideband PLL Frequency Synthesizers Lose Lock

By Pete Hanish, Applications Engineer, Texas Instruments

Abstract

Wideband frequency synthesizers have become widespread recently, enabling software-defined radios that address the diverse frequency bands in LTE, MC-GSM, WCDMA, CDMA, TD-SCDMA, and WiMAX infrastructure systems with shared hardware. Although several manufacturers offer built-in algorithms that automatically select from integrated multiple voltage-controlled oscillator (VCO) and capacitor array structures, many system builders find themselves wondering why their phase-locked loop (PLL) will not lock properly and consistently. With an eye on practical identification and correction methods, this article discusses common user implementation errors and fixes.