Design Of Digital Transmitter Hardware Platform Based On Software Radio

With the digital radio system gradually replacing the analog radio system,the SDR is getting people's attention and has been widely used in various fields of military,civilian and commercial.The software defined radio(SDR)is as much as possible to digitize the analog signal,simplify the analog front end of the transmitter,get the A/D conversion closer to the antenna.And the SDR processes the digitized signal using the software to realize the system function in the whole transmitter system as possible as it can.At present,the receiving part of software radio has been studied to a mature status,but the emission part still remain to be further studied.This paper takes the digital transmitter hardware platform as the research subject,explores the basic principles of the digital transmitter deeply,and proposes a new digital transmitter system based on processing baseband signal through FPGA,the Delta-Sigma modulation and transceiver conversion from two key technologies,namely the baseband processor for digital transmitter and digital frequency conversion.Aiming at the new digital transmitter building hardware platform presented in this paper,the design of hardware circuit platform transmitter concludes FPGA core circuit,power supply circuit,the system clock circuit,the peripheral module circuit and frequency conversion interface circuit.The FPGA core circuit comprises an FPGA chip and an FPGA configuration circuit,the peripheral circuit module includes SRAM circuit,SDRAM circuit,FLASH circuit,Ethernet interface circuit and an ASI stream input.Hardware circuit adopts six layers of high speed circuit design of PCB,the highest signal transfer rate up to 6Gbps,to ensure that the transmission of radio frequency signals.This design uses the SOPC(system System On Programmable Chip,on a progra mmable chip)which bulit by NIOS ? to design and tests the hardware module driver board,the driver frequency interface circuit of the key design,realizes the digital baseband signal directly on variable frequency to radio frequency required.Finally,this paper tests the circuit board design using the MDO4054-6 type hybrid domain oscillograph from Tektronix company as the hardware.The results show that,the signal through the digital transmitter,frequency of success expected by the baseband conversion to RF frequency(725.76MHz).Compared with the spectrum of the input baseband signal,the output signal bandwidth remains unchanged,the unilateral bandwidth is 1.89MHz,the spectrum does not produce distortion,at the same time the stopband attenuation is about 32dB,which meet the expected requirements.The experimental results indicate that,the design of the digital transmitter hardware system meets the design requirements,and also verifies the feasibility of the hardware design of the digital transmitter.In addition,by changing the frequency,modulation mode and the baseband test again the hardware platform The test results and before,verifying the digital transmitter hardware system designed in this paper meet the flexibility of software radio,without changing the hardware at the same time,only need to modify the software to upgrade system.