Improved acquisition and tracking performance of PLLs through signal injection

Abstract

In the communication we consider the use of signal injection to improve the acquisition and tracking performance of PLLs (PLLI). A dynamic model describing the PLLI behaviour is derived. Based on this model we show that by a proper design the injected signal can be used to improve the acquisition capabilities of conventional PLLs without changing the loop response. Experimental measurements of a PLLI, with a Colpitts VCO designed to allow current injection, are presented which show that this type of loop has wider locking range and a reduced acquisition time relatively to the conventional PLL. With this experimental set-up we also confirm that with low signal injection power the loop response remains identical if injection is made in quadrature.