Multilayer Broadband Baluns Target ADCs

Both cellular-inFrastructure equipment and high-end instrumentation feature multi-carrier, multimode receivers. With conversion rates to 125 MSamples/s, the AD9445 high-speed dataconverter from Analog Devices (www. is optimized for such receivers. Its sibling, the AD9446, operates to 100 MSamples/s. It targets instrumentation, medicalimaging, and radar receivers that employ sub- 100-MHz baseband intermediate frequencies. If those 14-/16-b dataconverters are used in conjunction with Anaren's BDBD0205F5050AHF or BD0310E5050AHF multilayer broadband baluns, designers will reportedly reap the benefits of a higher signal-to-noise ratio and improved spurious-free dynamic range (SFDR). Anaren explains how to best combine these devices in an application note titled, "Using Anaren's BDBD0205F5050AHF, BD0310E5050AHF Baluns with Analog Devices, Inc. AD9445 and AD9446 High Speed Data Converters."

The 17-page document, which is authored by Anaren's Ralph Pokuls and John Woods, begins by clearly explaining the role of baluns in ADC design. Also known as transformers, these passive devices provide an impedance transformation and convert single-ended signals into differential (balanced) signals. In ADC circuits, baluns are used to appropriately couple signals to the converter's analog inputs. The balun can be thought of as a common-mode filter, which rejects commonmode signals on the differential lines but allows differential signals to pass. Because the analog inputs to the AD9445 are differential, significant performance improvements result from the differential analog stages having a high rejection of even-order harmonics.

In high-frequency applications in particular, the performance of ADCs is highly influenced by amplitude and phase imbalances arising from the balun. The note details how these aspects can be modeled and defined via equations. It moves on to compare the SFDR, signal-to-noise ratio (SNR), and full-power bandwidth/input drive of two Anaren balunsthe BD0205F5050A00 and BD0310E5050A00 to Mini-Circuits' ADT-1-1 and M/A-COM's ETC1-1-13 wirewound baluns. Compared to the wirewound baluns, Anaren asserts that its baluns boast superior amplitude and phase balance at higher frequencies. These improved specifications lead to improved SFDR. According to Anaren, the baluns also promise high part-to-part repeatability through fabrication technology based on multilayer organic substrates as well as a small footprint and better gain flatness at frequencies above 100 MHz.

Anaren Microwave, Inc., 6635 Kirkville Rd., East Syracuse,NY 13057; (315) 432-8909, FAX: (315) 432- 9121, Internet:

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