Multi-level Frequency Accuracy Checking Method of 2FSK Signal for Railway Application

In the ZPW-2000 jointless track circuit system, a multi-level checking method is adopted to check the frequency accuracy of the frequency shifted square wave inside the FPGA, the frequency accuracy of the output signal of the digital-to-analog converter (DAC), and the frequency accuracy and amplitude correctness of the output full wave back-checking signal of the transformer. The first and second levels adopt the pulse count method to calculate frequency, and the third level adopts singular value decomposition (SVD), a matrix factorization technique widely applied in signal processing for its ability to extract critical features. This paper uses those methods to analyze the signal characteristics of the continuous phase frequency modulated signals produced by electronic equipment to ensure the accuracy of designed signals and fault detection during operation. The proposed closed-loop verification of signal accuracy can help identify the degradation failure of a key component at the signal generation chain.