Design Of Modulator For Ultrasonic Speech Communication

In the modern information warfare, with the development of electronic countermeasure's technology and equipment, battlefield electromagnetic environment became even worse, meanwhile communications and electronic warfare has become increasingly fierce, which limits the applications of radio communications in certain special tactical background . In order to ensure the safe and unhindered communication links, the study of the various military communications for the anti-jamming and anti-reconnaissance or anti-measurement technology and seek to adapt to the new environment in certain of the new means of communication becomes a very necessary. Based on that ultrasonic speech communication is proposed.This paper briefly introduces AM modulation, sampling theorem, direct digital frequency synthesis, and the basis of relevant theories; Then according to the specific requirements of the subject, an AM digital modulation scheme was proposed which is based on the basic principles of DDS and hardware platform of the combination of FPGA & microcontroller. Design software will be the ideological penetration of radio, the original use of traditional analog devices to complete all parts of the circuit through software programming method to achieve increased system flexibility. Secondly, the realizing method & formation of hardware and the design of software were introduced in detial; the hardware circuit is composed of AM modulation circuit and power amplifier circuit, inwhich AM modulation circuit includes the analog part, the digital part and the power supply part. It is mainly used to construct the platform of digital AM for the speech signal and the carrier signal; the power amplifier circuit is a single circuit board,which mainly amplified AM signal to drive transducer ,then the massage was transmitted in the form of ultrasonic. Moreover, the design & process of all parts of the hardware circuits were detailed, and the corresponding circuit diagrams of each part are presented. The software design of the system contains two major aspects. Firstly, the single-chip microcomputer programming, which mainly use the IAR Embeded Workbench development environment, in view of the human-machine interface's interactive tasks, achieve the function of AM modulation parameters settings. The second part of software is the FPGA design process. It is mainly used QuartusⅡsoftware development using VHDL and QuartusⅡembedded graphics editor of the schematic graphic input mixed programming approach, such as DDS unit, the modulator unit, the A / D timing schedule unit, the D/A timing schedule unit. These units, interconnected in the FPGA, achieve internal AM function. Finally, the modulation system is tested and the results show that the system can works normally and stability, and basically achieve the expected design requirements.