General-purpose instruments based on NI Flex II innovative technology provide the highest dynamic performance

The convergence of technologies has enabled system manufacturers to continue to meet user expectations, but it has also put tremendous pressure on R&D and test engineers to test more features while minimizing test time to get products to market as quickly as possible. Virtual instruments are an excellent test solution for overcoming these challenges by effectively combining rapid development software and highly flexible modular hardware to create user-defined test systems. The increasing demands and expectations of consumers are driving manufacturers to develop newer, more innovative products with more features to maintain their competitive position and profits. Telematics systems in cars are a classic example of the increasing number of features. A few years ago, cars were only equipped with cassette players and AM/FM radios. Then the compact disc came along, and automakers immediately integrated CD players into cars along with standard AM/FM radios and cassette players. Consumer demands and expectations continue to increase, and it is now common to see telematics systems that include CD/MP3 players, DVD players, AM/FM and satellite radios, GPS, and cellular phones. All of these technologies that were once implemented as separate devices can now be integrated into a mature and complex telematics system. The convergence of technologies has enabled automakers to meet user expectations and gain a foothold in a highly competitive market. But this puts tremendous pressure on both developers and test engineers, who need to test more functions while minimizing the testing time to meet time-to-market requirements. Let's look at it from the perspective of the automaker. Consider the cost of designing and developing a telematics system. A few years ago, designers might have only needed a set of traditional boxed instruments to design and test the limited functions in a cassette player. However, to meet today's challenges, designers must purchase new instruments to complete the testing of new functions in telematics systems. As the test system continues to expand, not only does the space begin to run out, but the expenses also exceed the budget. How great would it be if all these expensive and disparate instruments could be replaced with an integrated test system that can define functions according to specific applications and provide room for future expansion? Today, virtual instrumentation has become the preferred test solution to overcome these challenges. It combines rapid development software and highly flexible modular hardware to create user-defined test systems. Virtual instruments can provide: intuitive software tools for rapid test development; fast, accurate modular I/O based on innovative commercial technology; PC platforms that provide high accuracy and high throughput with integrated synchronization capabilities. Rapid Test Development Software As automation becomes a fundamental requirement for rapid testing of complex products, software has become an essential component of all test systems, from design verification to highly automated manufacturing testing. An integrated set of test development tools is needed to quickly deliver test systems capable of testing new features. These tools include test management, test development, and I/O drivers. Modular I/O The second important test technology is modular I/O, which includes technologies such as modular instrumentation and data capture. Modular I/O uses commercial chip technology to create low-cost, high-performance virtual instruments. The popularity of widely used commercial technologies such as ADCs, DACs, FPGAs, and DSPs has rapidly enhanced modular I/O functionality and performance. In many cases, the accuracy of virtual instruments exceeds that of traditional instruments. PC-Based Test Platform All modern test systems include a PC. The PC has become more than just a part of the test system, but is increasingly becoming an important integration platform: the center of the test system. Gigahertz processors, high-speed buses, widespread availability of software, ever-increasing performance, and extremely low prices have made the PC an ideal test platform. If you look at the performance evolution of the PC over the past 20 years, the only part of the test system that has seen the same level of performance improvement is the device under test itself. Universal Instrumentation for Dynamic Testing Let’s assume you are testing the audio and wireless functions in a vehicle’s telematics system. The instruments needed to perform the audio and wireless tests are an audio analyzer, an RF downconverter, and an IF digitizer. You can select three PXI or PCI modules and define the test system in software. It is obviously more beneficial if one device can be used for multiple purposes. Now you can use universal instruments for dynamic measurements to achieve this purpose. One such device is the PXI-5922 Multi-Resolution Digitizer from National Instruments (NI). With this digitizer, the user can adjust the sampling rate to obtain different resolutions. For example, at a sampling rate of 15MS/s, the module can provide 16-bit resolution. By reducing the sampling rate to 500kS/s through software, the same module (without any hardware changes) will provide 24-bit resolution. In this example, the PXI-5922 universal instrument can be used as both a 24-bit audio analyzer and a 16-bit IF digitizer.

Figure 1. Key points on the frequency-resolution curve for the NI PXI-5922 multiresolution digitizer.

Just as the DMM combines multiple DC measurement functions into one instrument, the PXI-5992 improves AC measurement capabilities by providing multiple instrument functions in one digitizer. Using the digitizer and software such as LabVIEW8, new virtual instruments can be created. Using such virtual instruments, better measurement performance can be achieved than many traditional instruments such as audio analyzers, spectrum analyzers, IF and I/Q baseband digitizers, DC and RMS voltmeters, and frequency counters. [page]

Figure 2. PX-5922 frequency-resolution curve compared to other digitizers at sampling rates up to 15MS/s.

Innovative Flex II ADC Multi-resolution Technology

This innovative multi-resolution technology is made possible by NI’s Flex II ADC. This analog-to-digital converter is an enhanced delta-sigma converter designed with a fully custom analog ASIC designed by NI. It achieves exceptionally high dynamic range over a wide range of sampling rates by using two innovative technologies: a 6-bit delta-sigma ADC instead of a single-bit delta-sigma ADC; and a patented digital linearization mechanism.

Single-bit delta-sigma ADCs can provide high resolution and high dynamic range for low-frequency applications. However, due to limited sampling speed, single-bit delta-sigma ADCs are not suitable for applications with dynamic signal frequencies exceeding hundreds of kHz. Multi-bit delta-sigma ADCs can provide high dynamic range at high frequencies, and linearization can remove the nonlinearity inherent in multi-bit delta-sigma ADCs.

Figure 3. FFT plot of a pure sine wave applied to a 6-bit delta-sigma ADC before and after linearization.

Figure 3 shows how nonlinearities in the ADC appear as harmonics in the frequency domain. The Flex II ADC uses a powerful FPGA and patented linearization technology to digitally remove these nonlinearities and provide a wider dynamic range at a higher sampling rate range. The increased dynamic range gives users the ability to analyze signals that would previously be lost in the noise of traditional instruments.


The Flex II ADC is a great invention, but it is useless if engineers cannot integrate it into digitizing instruments without compromising performance. The PXI-5922 multi-resolution digitizer has a state-of-the-art modular front end that fully exploits the high-performance Flex II ADC capabilities, freeing up the digitizer's available resources to deliver powerful performance. This digitizer provides the highest resolution and largest dynamic range on the market. As a result, it can not only be used as a general-purpose instrument, but also provides higher dynamic performance than the various stand-alone instruments it replaces. Figure 4 shows an FFT capture of a very pure 10kHz sine wave produced by a high-end generator. The PXI-5922 noise density can be as low as -170dB FS/Hz, and in this case the SFDR can be as high as -120dBc.

Figure 4. A high-end generator produces a very pure FFT capture of a 10kHz sine wave with noise levels as low as -170dB FS/Hz and SFDR as high as -120dBc.