Learn the advantages of LabVIEW FPGA and software design RF instruments

An overview of the number of wireless devices, the diversity of communication standards, and the complexity of modulation schemes are increasing every year.    And with each generation of new technology, the use of traditional technology to test wireless equipment, the need for a large number of more sophisticated testing equipment, the cost is also increasing. The use of virtual (software) instrumentation combined with modular I/O is a way to minimize hardware costs and reduce test time.   The new method of software design instrument allows the RF test engineer to reduce the test time with multiple orders of magnitude without the use of custom or special standard instruments.  Read this article to help you understand how to design and customize your RF instruments using the NI LabVIEW FPGA, as well as the benefits of your test system with software-designed instruments.

Brief introduction of
software Design instrument


  Over the years, test engineers have used software packages such as LabVIEW to implement custom RF measurement systems and to reduce costs as much as possible compared to traditional packaging instruments. The use of software design not only provides great flexibility, but also enables test engineers to leverage the latest PC,CPU and bus technology to improve performance. CPU has become the bottleneck of many high requirements RF test applications, CPU limited parallel mechanism and software stack will lead to delay, for some need to be measured according to the state of measurement or equipment (DUT) dynamic adjustment of Test incentive application, will affect the test results. In order to achieve the best RF test system effect, the need to combine the use of custom instrumentation hardware and multi-core technology, which allows the test system designers to find a low latency and high throughput balance point, thereby significantly reducing the test time. Although the performance of off-the-shelf instrumentation hardware has long been improved, NI is still committed to using Field Programmable gate Array (FPGA) technology to provide more open and flexible testing equipment. In short, FPGA is a user-definable high-density digital chip that allows test engineers to combine their custom signal processing and control algorithms into test hardware. As a result, the available RF hardware includes a number of advantages: high quality measurement techniques, and the inclusion of reliable, traceable measurements in its newest components, with a combination of highly parallel user-defined logic, which can produce a lower latency and can be associated with i/ o Direct connection for online processing and strict control loops. One case of such hardware is the NI pxie-5644r vector signal transceiver (VST). The device integrates the functions of vector signal generator and vector signal analyzer, and includes a user programmable FPGA for real-time signal processing and control. With more flexibility from FPGA, VST is ideal for custom triggers, device control to be tested, parallel testing, and real-time digital signal processing (DSP). Using LabVIEW FPGA to extend the application of LabVIEW to hardware customization Although FPGA has been widely used for custom motherboard design or as part of a usable device, user-defined FPGA has not so far been used in a large number of available RF equipment. This is mainly because the programming of these devices requires professional background knowledge. Hardware description Language or HDL, usually very difficult to learn, only the digital circuit design experts to be competent. LabVIEW FPGA modules can help a large number of engineers and scientists to access the latest FPGA technology. Using graphical programming methods, users can implement logical definition of RF instrumentation in hardware. In fact, LabVIEW's graphical data flow features are ideal for implementing and visualizing the parallel operations that can be performed on the FPGA. Although using LabVIEW to FPGA programming is still slightly different and requires additional learning, but it will be significantly less difficult to learn than HDL. Figure 1, using the LabVIEW FPGA module, users can customize the instrumentation hardware using familiar LabVIEW code. For RF applications, users can add modifications to implement custom triggers, device control, signal processing, and so on, based on a pre-built sample project. Many examples of LabVIEW FPGA projects can be used as a starting point for your RF applications, and these projects can also be applied on devices such as NI pxie-5644r vst. It is worth mentioning that the user can be based on the instrument data Movement mode (with the vector Signal Analyzer or generator has a similar custom start, stop and reference trigger display interface), or according to the data flow mode (for online signal processing or recording and playback applications) to the FPGA customization.

The comparison between the
software design instrument and the traditional method using FPGA based hardware in the RF measurement system can bring many advantages, such as the control of low latency equipment and the reduction of CPU load. More details on the different applications are described below. Using the interactive Device control method to improve the integration of test system in many RF test systems, digital signals or custom protocols are needed to control the devices and chips that need to be controlled. Traditional automated test systems can be sorted by the mode of the equipment to be tested, and the required measurements are performed at each different stage. Some intelligent automated test instruments (ATE) systems can be sorted between the device settings to be tested based on the measured values received. For any two cases, software design instruments including FPGA can reduce the cost and reduce the test time. The integration of measurement processing and numerical control into one instrument reduces the need for other digital I/O and does not require the configuration of triggers between devices. For some devices that must be controlled based on the measured data received, software design instruments can turn off loops in the hardware to reduce the high latency associated with making decisions in the software.


use hardware measurements to reduce test time and improve test reliability Although today's software based testing system can only parallel processing of a limited number of measurements, the software design instrument can achieve parallel processing without limitation, as long as the FPGA logic is used. The hardware parallel mechanism can handle a large number of measurement tasks or data channels without having to select the assigned measurement tasks. such as fast Fourier transform, filtering, modulation and reconciliation calculation, can be carried out in the hardware, which can reduce the amount of data transfer and processing CPU. Functions such as real-time spectrum masking, which use software to design instruments, can achieve higher rates than traditional packaging instruments. In addition, the low latency of performing measurement tasks in hardware means that the standard test system may only require a single measurement task at the same time, but it can perform dozens of or even hundreds of real-time measurement tasks simultaneously, increasing the quality of the test results and increasing the reliability of the RF test. Furthermore, since the measurement task can be performed continuously in the hardware and periodically sampled from the host test program, the user can be completely free from the fear of missing any important data. Figure 2. Using software design instruments, users can continuously collect data and perform tests (periodically sampling test results) without stopping the acquisition process to transmit information.


Fast reaching the optimal test conditions through closed loop feedback some RF tests require that the device setup or environment and the number of production processes to be tested need to be changed according to the measurement tasks received; This requires a closed-loop system, but it is often limited by the delay of the software stack. In many cases, you can close the loop directly in the hardware so that the CPU does not need to compute the next anchor point. This reduces the closed loop test time from several 10 seconds to fraction seconds.


a user-defined trigger to handle specific data using instrumental hardware has solved the delay problem of trigger behavior. However, by using software-designed instruments, users can integrate custom triggers into devices so that commands can be executed quickly in specific situations. Flexible hardware-based triggering means that users can set custom spectrum masks or other complex conditions to standard when capturing important measurement data or activating other instrumentation. Also, by selecting specific data in the hardware, users can be freed from the CPU for other important tasks. Rational application of software investment in the design process while this article is mainly about RF testing, engineers are increasingly using IP over the design and testing phases, shortening the time-to-market and drastically reducing the overall cost of testing. The digital signal processing algorithm can be defined by LabVIEW FPGA, and it can be reused as part of the device or component confirmation, so that no more test code should be written from scratch. This can accelerate the development of the test (start the test at the beginning of the design phase) and make the test coverage more complete. Figure 3. IP can be reused in the design and testing phases to reduce test development time and provide a more complete range of tests


Software Design instrument in the next few years, the manufacturer's defined instruments and functional instruments will undoubtedly continue to exist. However, more and more complex RF devices and product time-to-market pressures have driven a growing number of software-based instrumentation systems, and the continuation of these trends means that in the near future, software design instruments will gradually play an essential role in RF testing, and even in all test instruments. Software design instruments provide a high degree of flexibility, high quality performance, and the timeless nature of using instantly available hardware. When the system requirements change, software design instrument software investment will be retained through different modular I/O, and existing I/O can be changed according to the actual application.