15M-sample/sec, flexible-resolution digitizer heralds universal dynamic-measurement instrumentation
By Dan Strassberg -- EDN, April 14, 2005
Design and test engineers can now use one $6495 modular instrument to make a range of dynamic measurements, As the manufacturer, National Instruments, puts it, the PXI-5922 flexible-resolution digitizer is a universal measurement tool for dynamic signals just as the digital multimeter is for dc and low-frequency ac signals. Engineers can combine the module with the LabView 7.1 graphical environment for system development to create numerous types of instruments, such as ac voltmeters, audio analyzers, frequency counters, spectrum analyzers, and I/Q-modulation analyzers that sometimes exceed the performance of high-end traditional instruments with similar functions.
“Virtual instrumentation redefined how test-and-measurement systems were built,” says James Truchard, PhD, NI president and chief executive officer. “By providing a device that spans many different applications, the PXI-5922 flexible-resolution digitizer redefines how the hardware for virtual instrumentation is built. The module takes us a long way toward our goal of a universal measurement-instrument platform.”
Unlike traditional measurement devices, whose resolution is independent of sampling rate, the PXI-5922 uses the NI FlexII ADC that can sample with resolution of 16 bits at 15M samples/sec to 24 bits at 500k samples/sec. The NI FlexII ADC incorporates patented methods for reducing the linearity- and temperature-drift errors inherent in multibit sigma-delta ADCs. With the module’s large dynamic range and low noise, design and test engineers can often directly digitize low-level signals without the need for external signal conditioners, such as filters and low-noise amplifiers. Reduced signal conditioning improves measurement accuracy and reliability and can also save test-system-development time.
The combination of measurement flexibility and high dynamic range suits the NI PXI-5922 for a range of applications. With performance exceeding that of most commercially available ADCs, for example, the module is useful for characterizing and testing the latest DACs. For precision audio applications, the digitizer’s ability to acquire signals with 24-bit resolution at rates as high as 500k samples/sec means that engineers can capture high-order harmonics with wide dynamic range (Picture). The module’s 18-bit resolution at 10M samples/sec makes it an excellent digitizer for acquiring baseband I/Q signals in digital-communications systems.
For tight synchronization with other products, such as high-speed digitizers, arbitrary-waveform generators, and digital waveform generator/analyzers, the module is built on the SMC (Synchronization and Memory Core) architecture. This architecture, which accommodates onboard memory as deep as 256 Mbytes per channel and allows high-speed data streaming, enables the module to synchronize with multiple instruments and to hold typical module-to-module skew to less than 1 nsec. Engineers can use the module to create mixed-signal stimulus/response measurements. By synchronizing multiple modules, acquisition can expand to 1632 channels.
National Instruments, 1-800-258-7022, www.ni.com/modularinstruments.
