The Feature Frequency Computation Tool (FCT) simplifies test program development

1 Introduction

Digital signal processing technology provides engineers with great flexibility in developing special analog and mixed-signal applications. However, this increased flexibility also increases the possibility that engineers will have defects that are not easy to find when developing test programs, thereby reducing test performance.

2 Make sampling technology consistent with test frequency requirements

When performing analog DSP tests, engineers rely on complex correlated sampling techniques to ensure that the sampling and test frequencies are consistent. To achieve correlated sampling, the optimal solution that meets the following formula is required:

Where: M is the number of cycles in the sampling window; N is the number of sampling points; Ft is the test frequency; Fs is the sampling frequency.

To meet this formula, the test program writer must consider various restrictions: the ratio of M/N must be a prime number, and N must be an integer power of 2 to ensure correlation using fast Fourier transform technology. At the same time, N must be large enough to provide the required resolution, but not too large otherwise the test time will be too long. In addition, the correct solution must also address the physical limitations of the test equipment, such as special restrictions on sampling frequency or upper limits on resolution. The test frequency must take into account various possibilities, such as multi-harmonic testing. In addition, the choice of test frequency must take into account the FFT method, and different test frequency selections will make the results very complicated.

In the past, test engineers relied on spreadsheets or manual calculations to determine sampling parameters. This manual labor actually forced engineers to focus on parameter selection issues. And this manual method becomes very difficult when the test criteria include undersampling or oversampling methods. Even in simpler cases, this trial-and-error method makes engineers consider whether there are better parameter settings that can test more efficiently.

3 Use new software tools to determine sampling frequency and high-speed instrument settings

The unique frequency calculation tool (FCT) provided by leading ATE suppliers (such as Credence) is an interactive software tool that can help test program developers determine the sampling frequency in analog tests (Figure 1). FCT is a program development software tool in Credence's OctetTM system. The tool can calculate different solutions to avoid N values ​​that are too large or too small within the test system's capabilities. Therefore, FCT can find the best combination of parameter settings based on the test system configuration and specific application. With these parameter settings, test engineers can simply drag and drop parameter values ​​into Octet's Analog Waveform Tool (AWT) to generate waveforms.



In addition, Credence's Instrument Setup Tool (IST) simplifies test program development and high-speed instrument setup. In traditional systems, engineers need to understand the detailed commands of each instrument configured in the test system to develop test programs. IST eliminates this tedious work. Since IST stores information about the limitations and capabilities of the system instruments, the tool can provide a simple interactive method for generating C program code. During test program development, test engineers fill out a table in IST to describe the expected waveform. The parameter setting, signal capture and analysis required to generate the waveform are completed by IST. Test program developers no longer need to master the commands and programming mechanisms of different instruments, and can focus on higher-level test applications and optimize test methods .

4 Conclusion

Through automatic analysis methods, new software tools such as FCT can help test engineers save manual labor and get better test results. In addition to tools such as FCT and IST, leading ATE companies such as Credence are constantly strengthening the capabilities of test software to improve test productivity and quality.