Research On Sweeping Source And Human_computer Interface In VNA

VNA is an advanced measurement instrument which is developed based on microwave , micro-electronic and computer technologies . RF and microwave technology study become more and more popular, so more and more university students choose this subject for their major. Experim_ents is very important in technology study, so necessary instruments are needed. Of course, VNA is one of the most important Instruments in RF and microwave study. But VNA in market is very expensive and complex ,so it is not suitable for teaching. In this paper, an easy_to_use and cheap VNA is designed for teaching purpose.VNA is composed of microwave frequency sweep in source ,microwave circuit, control circuit, human_computer interface and software. And it is some kind of intelligent instrument controlled by MCU. DDS technology in sweeping source and human_computer interface technology is studied in this paper. A sweeping source circuit composing of ATmega16 and AD9854 is designed. And human_computer interface is realized in this paper.This paper's research focuses on two parts. That is frequency sweeping technology and human_computer interface.1. In the first part, three frequency_synthesis technologies YIG, VCO and DDS are introduced and their benefit and shortcomings are compared. Then this part's focus is on DDS which is a newer synthesis technology. It tells when DDS came out, how it develpe what its future will be. And its theory and core are studied deeply. Then a DDS sweeping source case is designed, including detailed circuit design, EMC concern about PCB design. Because DDS circuit is a typical analog and digital mixing circuit, EMI is very important problem to be solved. How to isolate analog circuit and digital circuit ? Search the way for revolve the interactive of high-speed signal race.2. In the second part, a human_computer interface is designed.It iscomposed of a 320×240 LCM, 5×5 keyboard and LPC2200 MCU whose core is ARM7TDMI. MCU is the heart of control unit. LCM is the display module for information output just like PC monitor. Keyboard array is the part for information input including control, digital input and so on.. Based on comparing all kinds of MCU, 32-bit embedded MCU LPC2200 is choosen for its outstanding performance both in technology and in price. LCD is choosing for displayingfor it is a green display technology. In this part, LCD and keyboard software is designed. It also can be called GUI---Graphic User Interface. This paper gives some concepts about how program turns.At last, some thoughts are given about the future of technology in measurement instrument.