Structure and composition of virtual digital oscilloscope
Virtual Digital Oscilloscope by a PXI bus multi function data acquisition card and the corresponding software. Install them on a computer running Windows PC, which constitutes a function powerful can store digital oscillograph. Digital oscilloscope's front panel as shown in Figure 1.

The data acquisition card
--- the design is used in the production of NI multi function data acquisition card PXI-6670E, and its main functions are as follows:
---64 single ended 32 analog input; 12 bit precision; 1.25MSPS sampling speed; 1.25MSPS disk write speed; + 0.05 ~ + 10V input range; two 12 bit analog output; 8 digital I / O lines; two 24 bit counter / timer.

The functions of the instrument.
- the cases of virtual digital oscilloscope with real-time data acquisition, spectrum analysis, window processing and filtering and other functions. In the main panel of the virtual digital oscilloscope data acquisition, spectrum analysis, window treatment, filtering function keys, press the corresponding button can enter the corresponding sub panel.

Software design and Implementation
The software development environment.
Virtual digital oscilloscope software design using the support value based on C language programming environment LabWindows/CVI.LabWindows/CVI, boolean type, text type and string data type, and the biggest advantage is to through the dialog box in the form of interactive operation to generate standard C program code. Also LabWindows / CVI provides very rich debugging tools, including stepping, breakpoints, variable view, window monitoring. These features make debugging more easily.

The main function module.
Virtual digital oscilloscope mainly by the software to complete the signal acquisition and processing, functional structure of the block diagram shown in Figure 2.
--- in the data acquisition panel is mainly completed the following functions: set the channel, set the sampling frequency, set the way, display waveform, etc., and its soft panel as shown in Figure 3.