The Design And Application Of Dual EGC Amplifier Based On Duplex HFC Network

HFC could not only provide better service for cable access television with hightransition quality and reliability, what more, duplex HFC network could build a favorablebidirectional communication architecture which could provide digital television signal, videoand data service.EGC amplifier undertook the mission of amplifying RF signal in the duplex HFCnetwork. Both the domestic and overseas, the RF amplifier’s working bandwidth is within862MHz, and the output ability is not enough to undertake the enormous users. Also, the highnoise in the up-stream becomes the bottleneck of the data service development based onCATV. In addition, the production in the market could not guarantee high stability whichmakes the maintaining costs higher and higher. To solve these issues, this paper analysis thespecifications of EGC amplifier and design an EGC amplifier with high performance bytheoretical analysis and simulation.This paper designs up-stream two stages circuit and down-stream three stages circuitbased on traditional two stages amplify. Simulation and calculation have been done to controlthe total Gain, distortion and noise figure of the EGC amplifier within the respectspecifications; other functional circuits have been added to guarantee the flatness of Gain;electric ATT and EQ have been design to realize the electric gain control feature; up-tiltcircuit has been added to compensate the isolation in lower frequency to ensure the gainflatness of the whole bandwidth.Auto gain control module has been designed based on automatic control theory withpilot signal to ensure the stability of Gain; down-convert and IF detection technology havebeen used to realize the hardware circuit.A RF diplexer with high isolation and low insertion loss has been design to prevent thesignal crosstalk between up-stream and down-stream; the diplexer’s topology is based onElliptic filter and simulation by ADS has confirmed and optimized the parameter; the splitpoint is convenient to adjust to adapt the DOCSIS3.1standard.PCB rework has been done to improve the performance of the amplifier by solvingseveral key issues such as reflection, distortion and spurious noise.Finial, systemic test of the demo have been done, including s parameter test, distortiontest, noise figure test and etc. The test result shows that: the max gain of up-stream is28dB,IMD3≥60dBc and IMD2≥60dBc when112dBuV output power,5.7dB noise figure; themax gain of down-stream is40dB and CTB/CSO≥64dBc when112dBuV output power,8.3dB noise figure; the specifications and stability improved compared to recentlyproductions both domestic and overseas.