—Four strategies for upset protection in NCO (Numerically controlled oscillator) generators are presented and compared in this paper 1. This work is motivated by the increased prevalence of single event upsets due to pro-cess/voltage/temperature variations coupled with the increased advancement of CMOS technology. The occurrence of these upsets in the GPS context (the system under the test in this paper) can lead to a loss of the GPS signal tracking, then the corresponding satellite signal must be re-acquired resulting in high energy expenditure and time delay. It can result also in a corrupted position given by the GPS receiver. Results of experiment using a GPS receiver design are presented in this paper to evaluate the performance of proposed methods. This work can be extended and generated to any system using feedback loops information.