Design of Multifunctional Signal Generator Based on LabVIEW

0 Introduction

Signal generator is an essential part of many electronic devices, especially test equipment. It is used to input reference source signals to the device under test, and analyze and study the status of the device under test by receiving information returned by the device under test. When measuring or evaluating the accuracy of a signal generator, the most basic and important part of it, namely the sine signal, is mainly tested. The important indicators for testing the performance of sine signals are frequency accuracy and frequency stability, signal-to-noise ratio and harmonic distortion.

Programming is troublesome for engineers and technicians. LabVIEW software uses a graphical programming language that is intuitive, simple and easy to operate. Users can create programs at will using LabVIEW and call them as subroutines to create more complex programs. The calling level does not limit the LabVIEW method of creating and calling subroutines, making the created program structure modular and easier to debug, understand and maintain. At the same time, LabVIEW can virtualize many conventional instruments and complete different functions through computer simulation, which can save equipment investment and improve efficiency. Therefore, it is of great significance to realize a multi-function signal generator based on LabVIEW.

1 Signal Generator Software Design Idea

To design a virtual signal generator, we must first design the front panel. The design of the front panel mainly needs to consider what functions the designed signal generator will achieve. Then, according to these functions, select the corresponding controls in the control palette and place them in the corresponding positions of the front panel. There are also certain requirements for placement, so that the front panel looks more coordinated. The next step is the design of the back panel. The design of the back panel requires the use of function templates. According to the functions that this program needs to achieve, select the corresponding function in the function palette. Since the program is not executed only once, it involves a loop structure. The loop structures used in the program in this article include while loop structure and conditional structure. After the program is successfully debugged, a virtual signal generator is generated.

2. Front panel design of the signal generator

First, three waveform display windows should be added. The first two windows are used to display the two basic signals, and two knobs are configured for the first two windows respectively to control the amplitude and frequency of the signal. Then, a drop-down menu selection control is configured for each of the two windows to select the type of signal. The available signal types are sine wave, triangle wave, square wave and sawtooth wave. The third window is used to display the power spectrum of the signal, and two drop-down selection boxes are added to the third window to select the window and filter, which can be used for windowing and filtering. Finally, in order to facilitate the observation of the signal, a stop button must be set to facilitate the control and observation of the static signal waveform. In order to facilitate data recording, a blank box can be added above the signal waveform display to record the experimental data in the box. The front panel design of the signal generator is shown in Figure 1.

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3. Rear panel design of the signal generator

Since the signal generator designed in this paper can display the power spectrum of the signal, a fast Fourier transform control needs to be added to the program flowchart. Since windows and filters are required, two loop structures must be added to the program flowchart. These two loop structures are used for window control and filter selection control respectively. Since there are two signals, two windows and two filters are added in the while loop. The windows available are uniform, Hanning window, Hamming window, Blackman-Harris, Exact-Blackman, Blackman, Flattop and 4 Term Black-Harris. The filters available are Butterworth and Chebyshev. The outputs of the two loop structures are connected to the FFT power spectrum module respectively. The main function of the FFT power spectrum module is to calculate the average self-power spectrum of the time signal. The data type connected to the time signal input terminal determines which polymorphic instance is used. The output of the FFT power spectrum module is connected to the waveform display window using an array module, so that the power spectrum of the signal can be displayed in the third window. In order to facilitate data recording, a string function can be added to the program box, and a blank box can be displayed in the front panel to record the data that needs to be recorded during the experiment.

4. Block diagram of the signal generator

The flow chart of the signal generator is shown in Figure 2.

5 Conclusion

The designed signal generator can display two signals in two waveform display windows, the phase and amplitude of the signal are adjustable, and the power spectrum of the signal is displayed in the third waveform display window. The signal generator designed based on LabVIEW software proves that virtual instruments have powerful instrument design functions.