Integrating SMT Synthesizer Solutions Into Wireless Designs

Introduction

Today's high performance, low-cost, SMT solutions for frequency generation greatly simplify the designer's task in developing wireless products. Properly interfacing these devices into the circuit, however, is essential to achieving maximum performance. This article highlights some primary areas of concern, some analysis methodologies, and suggests possible solutions.

Power Supplies

Clean sources of regulated DC power are essential in minimizing spurious signals from synthesizers. You can calculate the quality of the supply necessary by the following formula:

Where:
Fs = Spur Frequency
dBc = Desired Spur specification in dBc
Pushing Figure = Pushing Figure in Hz/Volt

For example, with a spur frequency of 1 kHz, a spur specification of –80 dBc and a pushing figure of 3MHz/volt, the ripple voltage on the supply must be no greater than 47nV rms. It is good design practice to allow for a margin in the spur specification. For this example, we use –70dBc plus a 10 dB margin for -80 dBc.