Research And Implementation Of Demodulation Technology Of Telemetry Data

With the increase of various measurement parameters and performance requirements intelemetry system, more complete function and stable performance of the PCM (pulse codemodulation) demodulator is demanded. However, there is no PCM demodulation equipmentand foreign PCM demodulation card although perfect performance but it is expensive anddifficult to repair, therefore, it is necessary to design our own PCM demodulation card.The research status and development trend of PCM telemetry system is introduced andthe main content is receiving and demodulation of the programmable PCM data flow. Basedon the application environment and function need to achieve of the PCM demodulation card,the overall scheme of this design is put forward, and introduces the key technology aboutsynchronous clock accurate extraction, high precision clock and frame synchronizationlocking of arbitrary frequency. After the introduction of hardware circuit, detaileddemodulation of PCM data logic implementation is described, firstly analyzes the advantagesand disadvantages of present digital PLL used with1bit synchronizer two bit synchronizationmethods, and then illustrates the method by using the DDS to achieve high precision clockwith any frequency, on this basis, a design of bit synchronization clock extraction circuitanti-interference ability strong, fast bit synchronization, clock output stable; then introducesthe implement method of variable frame structure data frame synchronization in this paper,and the design of fault tolerance mechanism and the protection circuit to increase thereliability of the frame synchronization. Finally introduces the realization of data upload FIFOand the implement of communication protocol.At the end of this paper, hardware test and function test of demodulation card iscompleted in the control of the PC software, after connecting to the testing equipment.According to the test result, the demodulation card can realize1-10MHz code rate,demodulation different code type and different frame structure of the PCM data stream.