Improved acquisition and tracking performance of PLLs through signal injection

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