On the design of an offset-PLL modulation loop for the EGSM band

Issues associated with the system design of an offset phase locked modulation loop (OPLL) are presented in this paper. The sources of spurs within the loop are all explained in detail. In order to meet the transmission mask stringent requirements for the EGSM band, a criteria for choosing the IF frequency is presented. Additionally, the paper gives the design procedures for calculating the required suppression of the offset mixer spurious signals by the offset mixer and feed back filter with respect to the IF signal.