Digital Demodulation Algorithm for Multi-Tone FM Signal in New Type Track Circuit

The multi-tone frequency modulation （FM） signal transferred through track circuit in automatic train control （ATC） system is analyzed. A digital filter with ideal sloping shape in frequency domain is designed for frequency discrimination. With this filter, the FM signal is converted into AM-FM signal by frequency-to-amplitude conversion. The modulating signal is finally extracted from the envelope of the AM-FM signal. Simulations show that the digital demodulation method could accurately recover the modulating signal in low signal noise ratio （SNR） circumstance, and has good performance in suppressing interference of harmonies of traction current frequency. The feasibility of the proposed method is proved in a hardware system based on SHARC DSP.

Quantitative analysis on coupling of traction current into cab signaling in electrified railways

Cab signaling apparatus is the critical equipment for ground-vehicle communication in electrified railways.With the rapid development of high-speed and heavy-haul railways,the immunity to unbalanced traction current interference for cab signaling apparatus in the onboard train control system is increasingly demanded.This paper analyzes the interference coupling mechanism of the ZPW-2000 track circuit.Based on electromagnetic field theory and the actual working parameters,a calculation model is established to complete the quantitative research of the cab signal induction process and traction current interference.Then,a finite element model is built to simulate the process.The simulation results under the signal frequency,fundamental and harmonic interference are all consistent with the theoretical calculation results.The practical measurement data verify the coupling relationship between cab signal inductive voltage and rail current.Finally,an indirect immunity test method applying this relation for the cab signals is proposed,and the voltage indexes of the disturbance sources are determined,i.e.,the test limits.The results provide an accurate quantitative basis for the cab signaling research and design of the immunity test platform;besides,the proposed indirect test method can simplify the test configuration and improve test efficiency.

A Histogram-Based Static Error Correction Technique for Flash ADCs: Implementation

In this paper, we focus on practical issues in implementing a calibration technique for medium-resolution, highspeed flash analogtodigital converters （ADCs）. In [1], we theoretically describ the calibration technique and perform a behaviorallevel simulation to test its functionality [1]. In this work, we discuss some issues in transistorlevel implementation. The predominant factors that contribute to static errors such as reference generator mismatch and trackandhold （T/H） gain error can be treated as inputreferred offsets of each comparator. Using the proposed calibration technique, these errors can be calibrated with minimal detriment to the dynamic performance of the converter. We simulate a transistorlevel implementation of a 5-bit, 1 GHz ADC in a 1.2 V, 65 nm CMOS process. The results show that DNL can be improved from 2.5 LSB to below 0.7 LSB after calibration, and INL can be improved from 1.6 LSB to below 0.6 LSB after calibration.

Research on the performance of heavy-haul rail breakage detection using track circuit

Rail breakage is one of the major safety risks in railway transportation.Because of the large axle weight,high density and large capacity of the heavy-haul railway,the damage to rail caused by heavy-haul train wheels will be more serious than that caused by ordinary passenger and cargo trains,resulting in a higher frequency of rail breakage.Taking the Daqin Railway Line as the research object,this paper analyses and discusses rail breakages occurring in interstation tracks and in-station tracks by establishing the ZPW-2000A track circuit calculation model considering the land leakage resistance between the rail line tracks;introduces the defining standards and measurement index of the broken rail coefficient to quantitatively analyse the influence of various influencing factors on the rail breakage inspection performance under the most unfavourable working conditions;and compares the model simulation data,the laboratory model data and the field test results to verify its effectiveness,so as to provide a reference and theoretical basis for the subsequent improvement and solution of the heavy-haul railway rail breakage problem.