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Maxim > Design Support > Technical Documents > Application Notes > A/D and D/A Conversion/Sampling Circuits > APP 3176
Maxim > Design Support > Technical Documents > Application Notes > High-Speed Signal Processing > APP 3176
Keywords: MAX5886,MAX5887,MAX5888,MAX5195,digital-to-analog converters,dacs,high-
performance,communications
APPLICATION NOTE 3176
Digital-to-Analog Converters (DACs) for High-
Performance Communications
Apr 27, 2004
Abstract: Two new digital-to-analog converters (DACs) from Maxim address the highest levels of dynamic
performance in communications and instrumentation systems. The MAX5886/MAX5887/MAX5888 12- to
16-bit converters provide excellent dynamic performance at exceptionally high sample rates and low
power levels, and the 14-bit MAX5195 provides the greatest dynamic range available for production DACs
operating at sample rates up to 260Msps. Both are available in small, surface-mount packages. These
DACs also support the generation of multiple carriers in UMTS, CDMA, and GSM systems.
Superior information bandwidths, required to support the exchange of digital information in modern
communications systems, are achieved through a variety of modulation and encoding schemes. Such
schemes demand greater dynamic performance in the transmitter's signal processing chain. Applications
such as UMTS, cdma2000™, and GSM/EDGE also call for greater dynamic performance as they
approach the requirement of multicarrier generation from a single, signal-generating source.
UMTS requires up to four carriers per transmitter. For GSM/EDGE and cdma2000 applications, four to
eight carriers may be desired for a single transmitter. The generation of multiple carriers requires
substantially more dynamic range in the signal path. As the generator of this complex modulation
waveform, the DAC has become the performance-limiting element in the signal path.
UMTS base stations are now introducing multicarrier signal generation. These base stations, therefore,
require DACs that meet the UMTS standard with adequate margins. Also helpful in this application are
DACs that correct power-amplifier nonlinearity by introducing digital predistortion to the signal. That
characteristic alone can increase the DAC's required signal bandwidth by a factor of three to five. Thus,
the signal bandwidth necessary for four UMTS carriers (as high as 100MHz) demands higher sample
rates and higher analog-output frequencies. The 500Msps update rate of the MAX5888 is designed for
such applications. This device delivers the performance defined above and surpasses the UMTS
specifications for up to four UMTS carriers.
The accuracy and signal bandwidths of such DACs also support communications systems that employ
higher orders of QAM. Modulations up to QAM256 require wider dynamic ranges to accurately generate
these modulated waveforms.
Transmit waveforms in GSM/EDGE systems demand even more dynamic performance from the DAC. The
generation of multicarrier signals pushes SFDR, IMD, and SNR values to extremes. For those demanding
applications, the MAX5195 offers the highest SFDR, SNR, and IMD specifications in the industry.
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