Microwave Engineering Europe - March 2008 - (Page 14)

14 WIRELESS INFRASTRUCTURE — RECEIVER DESIGN Figure 3: Evaluation circuit schematic. be attained when the baseband traces are placed on a separate layer. On the DC1048A demo board, the RF and LO input traces are routed on the top metal layer from opposite ends of the PCB. The four baseband outputs are routed on the bottom metal layer, thus separating them from the RF and LO inputs by two internal ground layers. The baseband output traces are equal in length to preserve proper phase relations. Proper ﬁltering of unwanted high frequency mixing products at the baseband I and Q outputs is also important to maintain superior linearity. The most convenient method is to terminate each baseband output with a shunt capacitor to ground, placed as closely as possible to the IC’s baseband output pins. The capacitor value should be selected to optimize IIP2 performance depending upon the signal bandwidth. Summary and conclusions High performance I/Q demodulators such as the LT5575 enables basestations to take advantage of the intrinsically low cost direct conversion radio architecture. With a good understanding of the issues of direct conversion receivers reﬂected in proper layout of the printed circuit board, the dynamic range performance of even the most demanding applications can be realized. Such direct conversion design results in a simpliﬁed receiver, relaxed ﬁltering and the reduced components from using fewer stages. But the real cost beneﬁt comes about with demodulation to low baseband frequencies. Lower cost components such as low frequency ampliﬁers, ﬁlters, and A/D converters can now be used. Better still, the resource requirements for the baseband DSP is reduced considerably, realizing the full cost advantage. Reference [1] RF Microelectronics, Razavi, Behzad, 1998, Prentice Hall, ISBN 0-13-887571-5, pp. 129-138. Figure 4: Top side of evaluation board. Company Information Figure 5: Bottom side of evaluation board. Linear Technology Corporation www.linear.com MICROWAVE ENGINEERING EUROPE Free subscription at: www.mwee.com/subscribe Microwave Engineering Europe ● March 2008 ● www.mwee.com 011_012_013_014_MWEE.indd 14 20/02/08 12:27:21 http://www.linear.com http://www.mwee.com/subscribe http://www.mwee.com

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Microwave Engineering Europe - March 2008 News Contents Comment Wireless Infrastructure: A Direct Conversion I/Q Demodulatordrives Favorable Basestation Cost-performance Metrics Wireless Infrastructure: Mobile World Set to Reshape the Internet RF Amplifiers: Latest Advances in RF Amplifiers Include a CMOS PA Operating at 77 GHz and Significant Advances in PAs for WiMAX and Broadband Applications Many Applications Still Require Unique Performance Benefits of BeO ACE Automated Circuit Extraction Returns to Real Design by Exploring Design Alternatives and Changes in Seconds Exceeding the Standard for Wireless Sensor Networks Products Calendar

Microwave Engineering Europe - March 2008

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