Research And Implementation Of Virtual Instrument Based On FPGA

In the field of electronic measurement technology, there constantly emerge much new testing method and new test theory. The role of traditional instruments is becoming more and more limited. In order to update the traditional test equipment, much time and money is needed to design the complex circuits, which is very inconvenience in the electronic measuring. The use of "virtual instruments" as test equipment does not need to change the underlying hardware circuit, but only need to change the host computer software, that will shorten the development time.Because the price of the traditional testing device is high, it is difficult to meet the use of all students. What’s more, the test instrument, which the school spent a lot of money to buy, a small part of its function will be used, but the function we need cannot be met. So the efficiency in the use of the instrument is restricted. In addition, in order to improve the conditions of the laboratory, new equipments are needed, which will spend much manpower and material resource, and the development of laboratory will be restricted. The emerging of virtual instrument completely changes the above situation.In view of the above situation, this paper designs the method of acquiring and processing signals which is based on combining of the data acquisition card and the virtual instrument. In the system, FPGA is the controller chip, using internal logic resources inside the FPGA to generate the NIOS soft-core processor, Some digital integrated circuits and sequential circuits. Some controlling command data sended to the NIOS processor in PC through USB interfaces. NIOS processor receives the commands and sends controlling instructions to manage the peripheral chips, so it achieves to be a source of signals and can also get analog signals.The system generally works as follows:external analog signals firstly pass the signal conditioning circuit, which adjusts the input signals to within the scope of the A/D chip. Then NIOS processor converts the analog signal to digital signal by A/D chip: firstly, locking the convertion result is stroed within the FPGA; sencondly, writing the digital data into external SRAM under the control of clock signal; if the SRAM is full, NIOS processor upload data from SRAM to a PC through CH376a kind of USB managed chip. In PC, LABVIEW can process the uploading data.Except the data acquisition function, the system also has the function of the signal source output. The signal’s frequency is adjustable, and the output signal can be sine wave, triangle wave and square wave. The communication between host computer and the underlying CPU is connected with the external code or application software which provided by LAB VIEW dynamic link library (DLL). The underlying data acquisition boards mainly to complete the data acquisition and signal source output function. The main task of PC is to control the operation of the underlying CPU and to display the waveform of the data collected.