A Novel Frequency Control Loop for Tunable Notch Filters

In this paper, a novel frequency control loop system for tunable notch filters is presented. The frequency control loop is designed for automatically tuning a microelectromechancial systems tunable notch filter, which has 22-dB rejection in the notch band and less than 0.8-dB insertion loss over a 5-MHz passband bandwidth in the International Mobile Telecommunications band (2.1 GHz). The filter frequency control loop is based on sensing the reflection phase change of a reference signal (in this case, the transmitter carrier) and is developed to track the transmitter operation frequency.