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Maxim > Design Support > Technical Documents > Application Notes > A/D and D/A Conversion/Sampling Circuits > APP 1917
Maxim > Design Support > Technical Documents > Application Notes > Basestations/Wireless Infrastructure > APP 1917
Maxim > Design Support > Technical Documents > Application Notes > Communications Circuits > APP 1917
Keywords: local oscillator, buffer, splitter, LO, amplifier, cellular, basestation, UMTS, GSM, DCS, PCS, RF
output power, mixer, temperature control, temperature compensation, Wilkinson splitter
APPLICATION NOTE 1917
Simplifying Tomorrow's LO Drive Designs with the
MAX9987-90 Family of LO Buffers/Splitters
Mar 06, 2003
Abstract: The following article provides an insight into the features and functionality of Maxim's new LO
buffer/splitter family MAX9987 and MAX9990. The paper covers specified parameters and their importance
and impact on system applications such as cellular basestations and concludes with practical applications
circuits, which configure the buffer/splitter circuits to adjust output power levels analog and digital as well
as compensate for temperature fluctuations.
Introduction
In today's competitive market, wireless basestation designers are
faced with the daunting task of driving down product costs while
maintaining superior levels of radio performance. Cost can be cut by
reducing DM (direct material) expenditures, part count, design time,
variability in performance, and by designing out system failures. At
the same time, cellular operators are demanding higher density
systems which pack two to four times as much hardware into the
footprint of current basestations.
A common solution is to employ greater degrees of circuit integration throughout the receive and transmit
lineups. The MAX9987/MAX9990 family of LO buffers/splitters have been designed with this goal in mind.
These components improve the performance of the LO drive lineup by offering exceptional P
OUT
variance
control, isolation, and noise performance-all critical parameters for optimizing passive mixer designs.
An overview of typical LO drive circuits is provided below, with a description of how the
MAX9987/MAX9990 family of parts can be optimized for virtually any LO drive application.
Challenges Associated with LO Drive Designs
A typical LO lineup requires a buffer amplifier to isolate and drive a passive mixer from a VCO with
relatively low output power. Most passive mixers require drive levels ranging from +14dBm to +20dBm.
However, simple amplification of the VCO signal is not sufficient for optimizing mixer performance. A key
requirement for any LO lineup is to maintain a nominal drive level despite temperature, voltage and VCO
drive variations. Failure to contain LO drive variance can lead to degradations in receiver sensitivity and
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