Design Of Virtual Digital Oscilloscope

Oscilloscope is widely used in electronic measurement, test equipment and many other applications .it is essential in observing analog and digital circuit,analyzing the problem of the experiment. With the development of computer and electronic technology, the virtual instruments were invented. Virtual Digital Oscilloscope is one of many virtual instruments and has lots of advantages.Virtual machines have the advantages of high-performance, extendibility, less development time, and the perfect integrated functions. there are five major characteristics:①with variability,multi-layered the control panel ;②powerful signal processing capability;③user-defined function, performance;④standard and powerful interface bus, board and corresponding software;⑤virtual instrument with a short development cycle, low cost, easy maintenance. Virtual Digital Oscilloscope as a virtual instrument, it has very powerful features, apart from the majority of traditional oscilloscope functions, also has a lot of the traditional functions of oscilloscopes do not have such as: spectral analysis, the window treatment and add features such as digital filtering. From which we can see a powerful virtual instrument, and its advantages can not be replaced. With the electronic measurement technology, traditional technologies can not meet a lot of time measuring our needs, so vigorously develop the virtual instrument technology is necessary.The implementation of a virtual digital oscilloscope following three modules: data collection boards, USB modules, oscilloscope interface. Analog signals can measure the periodic signal of maximum 10MHz, peak - peak (Vp-p) 20 V. Data collection board, which is the core of this design , using of FPGA (EP2C5T144C8) as the master chip, can accurately capture the test signal .USB module implement communications, realize PC-acquisition boards and data and command transmission. The Oscilloscope panel using graphical LabVIEW programming language to realize is easy to operate and beautiful. Let us have a brief introduction about the functions of these three modules.Data collection board's main function is to get a analog signal, equally that transfer the analog signal into the digital signal, namely:the binary signal. It is the most important throughout the design of hardware, which includes a number of hardware sub-circuit, there is: coupling circuit, program-controlled amplifier, programmable attenuation circuit, shaping circuit, trigger circuit, FPGA control circuit, cache circuit, A/D conversion circuit. Program-controlled amplifier functions are too small to put the signal amplitude (A/D sampling should not signal) due to enlarge in order to carry out A/D conversion; program-controlled attenuation circuit functions are too large amplitude of the signal attenuation due to A/D converter, and amplifier circuit which are subject to the control FPGA; put plastic circuit under test into a symmetrical square wave signal in order to FPGA signals to the measured frequency measurement; trigger circuit to trigger the selection based on user to control the ADC's acquisition ; FPGA control circuit board controls the entire collection of various operations, it is the master who, such as: control of amplification (or attenuation) of a multiple of the sampling rate ADC control, and USB modules, implementation and communication, it is the entire data acquisition the core board to assume the role of command; cache temporary circuit A/D sampling data to ease the USB module and the PC does not match the speed of contradictions; A/D conversion circuit to good analog signal conditioning to convert to digital signal.USB module is mainly responsible for data collection boards and PC-communication. This is mainly consist of single-chip module (STC89C52) and USB controller chip (PDIUSBD12) composed of single-chip USB controller , USB1.1 implementation of communications, can achieve 1M B/s data transfer rate.Besides single-chip and FPGA communication, it has the responsibility for implementation of the USB protocol, and the underlying drivers connections; USB controller chip is responsible for the parallel signals into serial differential signal. Oscilloscope interface achieve data processing, these operators are done by LabVIEW. First LabVIEW read out the data and then proceed to restore the waveform, the design uses a sinusoidal waveform interpolation to restore, and then lines of wave digital filter, the FIR low-pass filter, and finally show the waveform. The virtual digital oscilloscope realize adjustment of amplitude, time-based control, parameter measurement, the trigger selection. Rate regulation and the traditional general-purpose oscilloscope, the oscilloscope by adjusting the waveform of coordinates to achieve the adjustment; time base oscilloscope control and GM are the same; parameters implementation under test measured the peak signal - peaks, high (peak), low (peak), frequency, cycle measurement of these parameters. Trigger selection can be based on user selection required inside and outside the trigger of two ways.Virtual Digital Oscilloscope has been debugged, with more satisfactory results. Experimental measurement of the signal source in various frequency sine wave, square wave and triangle wave . These waveforms are more accurate measurements, but the parameters of the measurement problem also exist. Low-frequency (1MHz) in the measurement is very precise, high-frequency (greater than 1MHz) measurement is not accurate, especially in the measurement of amplitude. The attenuation becomes large with the increasing frequency. This is the virtual digital oscilloscope for improvement. Hope that the researchers found that later can be helpful. Trigger function has also been proved, with more satisfactory results. In general, the virtual digital oscilloscope is still more satisfactory results, designed to achieve the desired goal, can be applied to the actual measurement.