Research Of Broadband Quadrature Digital Modulated Signal Generation

As one of the most important instrument in communication system,Vector Signal Generator(VSG)is often used in the test of digital communication.Its performance determines the accuracy of the testing.With the continuous development of science and technology,the performance of digital communication system got great improvement.Thus higher requirements for source's accuracy and diversity are put forward.How to generate broadband orthogonal modulation signal is the key problem of the research of Vector Signal Generator.The requirements are also raised by rapid development of electronic in related fields.After analysis and research the technology of digital signal processing and communication under this background,this thesis focus design on the baseband part,which is an important composition of Vector Signal Generator.The system adopts the idea of software defined radio(SDR)and use the programmable logic gate array(FPGA)as common platform.The configurable baseband module is built on this platform,which will generate general and broadband digital modulation baseband signal.The baseband signal then will be moved to radio frequency by orthogonal mixing.Through the verification,this design can really produce correct FSK,PSK,QAM and other general digital modulation signal with baseband data rate from 1Ksps to 20 Msps continuously.The modulation signal quality is good and meet the design requirements.The main work of this design are as followed.The plan of the system clock generate.The design use the FPGA's internal PLL to generate a set of related clock with the reference of DDS's adjustable output clock.The baseband part is worked under the PLL's output clock.By adjusting the reference clock frequency and PLL's dividers' value,the FPGA part get continuous and adjustable clock.So the baseband rate can also be continuously adjustable.The design of baseband signal generation module.This thesis takes the M sequence as baseband data,which then will be processed by coding,mapping,filtering and interpolating.The shaping filter unit adopts the method of parameter set to design.Thus can make the filter's type and parameters configured dynamically.In this design,the interpolation radio can be adjusted by combining the HB filter and CIC filter.The design of frequency conversion module.This module is mainly made up by digital orthogonal mixing and analog orthogonal mixing.The analog orthogonal mixing will move the baseband to 100MHz~3GHz carrier frequency.While the digital orthogonal mixing will provide appropriate channel frequency offset in the condition of dual channel output.