Interference suppression using DPLL with notch frequency characteristic

The authors propose a new digital phase-locked loop (DPLL) with notch frequency characteristic (DPLL-N), which suppresses the low-frequency output phase fluctuation caused by interference. The loop consists of two first-order, multilevel, quantized DPLLs connected by an equivalent differentiator with two delay circuits. The system has the desired attenuation in the low-frequency band. The performance of the loop is analyzed theoretically and verified by computer simulation. It is found that the output phase fluctuation caused by the interference can be suppressed without suppressing the modulated signal