| ADSL is one kind of fashion wide band internet interface style. ADSL Modem is the Customer Premise Equipment of the ADSL system. This thesis summarize the Modem's present design condition, make a comprehensive analysis and comparison to the technical principle and system construction of the different type of Modems. Based on the analysis and comparison, the basic skeleton of the ADSL Modem based on USB interface is determined, and than the detailed design of the Modem's hardware and software is given. The main works been done as following:1. The scheme designAfter the elaborate analysis of the ADSL Modem's performance demand, the hardware basic skeleton of the ADSL Modem based on USB interface is determined, it is USB interface + ADSL chipset, the basic construction of the hardware circuit is formed by them.In the USB interface section, the CY7C64613 chip, which is one kind of USB interface chip of the Cypress Corporation with a CPU, is used. The chip has two cores, one USB core and one 8051 core. The USB core has the intelligence to function as a full VI. 1 USB device. The 8051 core makes the chip programmable. In this scheme, the 8051 core is the CPU of the Modem.In the scheme, the AD20msp930 chipset AD6440 + AD6449-48 of the Analog Devices Inc. is selected as Modem's ADSL chipset. The chipset is designed for ADSL Modems, has a high performance-price rate. AD6440 is the analog front-end chip of the Modem, the main task of the chip is to complete the signal's A/D^ D/A conversation; AD6449-48 is the framer and control chip of the Modem, the main task of the chip is to complete the data framer and control the line work mode.The hardware blocks are designed around the three chips working demand, and their link relationship is determined by the three basic chips, too.2. The hardware designThe hardware design is carried out based on the USB interface chip and ADSL chipset. According to the three main chips working requirement and the ADSL signal's process demand, the hardware circuit is separated to 9 blocks, they are CY7C64613 chip and its interface circuit, FPGA and its interface chip, control block of AD6449-48 chip, payload block of the AD6449-48 chip, AD6440 chip, transmit path, receive path, hybrid circuit and power supply circuit.vCY7C64613 chip and its interface circuit include three chips and their working circuit. The chips are CY7C64613 chip, EEPROM chip and RS232 interface chip. CY7C64613 is the USB interface and CPU chip, it not only is the interface chip between the ADSL Modem and PC, but also is the CPU of the Modem. EEPROM is the program memory of the CPU, and it is used for CPU running codes keeping. RS232 interface chip supply a RS232 serial port for the CPU and PC, by which the running state of the ADSL Modem can be supervised.FPGA and its interface chip include two chips and their working circuit. FPGA is used for the time conversation between CPU and AD6449-48, at the same time, it is the data buffer of the internet data. The interface chip of the FPGA is used for the logic downloading of the FPGA.Control block of the AD6449-48 chip has a FLASH memory, the DSP code of the AD6449-48 chip is kept in the memory, and the DSP code is used for the working mode control of the AD6449-48 chip. Payload block of the AD6449-48 chip has the data framer function.AD6440 chip is the analog front-end chip of the ADSL Modem. It is main used for signal's A/D> D/A conversation.In transmit path, the current feedback circuit is used to enhance the transmit signal's drive capacity; in receive path, the voltage feedback circuit is used to improve the receive signal's capacity of discernment. Hybrid circuit converges the transmit path and receive path into one signal path to connect with the Central Office.Power supply circuit supply all devices voltage and current that they need for work.All the hardware support circuits supply the good material base for the high performance Modem. 3. The software designAccording to ADSL Modem's working principle and the special requirement... |
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