ETC CX74038

Dual Fractional-N
Synthesizer PLL Family™
CX72302 and CX74038
Conexant’s synthesizer phase-locked loop (PLL) family, which
comprises the CX72300, CX72301, CX72302 and CX74038 dual
fractional-N synthesizers, sets a benchmark for performance
and functionality. These fractional-N synthesizer ICs resolve
output frequency step sizes below 100 Hz. As precision tuners
in next-generation narrowband and multiband digital radio
products, these chips overcome the traditional trade-off
associated with obtaining ultra-fine frequency resolution
and low-phase noise performance.
Alternative solutions are unable to resolve step sizes below
200 KHz without dividing the crystal reference frequency many
times, a technique that induces unwanted phase noise, degrades
signal integrity and contributes to the cost of radio systems,
potentially forcing designers to use a more expensive voltage
controlled oscillator (VCO). While other solutions sacrifice phase
noise performance to increase resolution, Conexant’s fractional-N
synthesizer family employs a high internal reference and delta-
Distinguishing Features
sigma (DS) technology to achieve both excellent phase noise
performance and fine frequency resolution in a single chip.
• Industry’s most comprehensive
dual fractional-N synthesizer family
In addition to offering fine frequency step size and low phase
• Fast settling time (down to 100µs)
noise, the Conexant synthesizer PLL family offers fast frequency
• Ultra-fine step size of 100 Hz or less
settling time, a performance feature required by current and
• Phase noise as low as -95 dBc/Hz
future wireless network applications such as GPRS and W-CDMA.
• Low spurious noise
This feature enables such applications to send a signal and
quickly reset to send another signal to meet data throughput
The Design Solution
CX72300 Specific Performance
RF engineers face many design problems when using
• Dual 2.1 GHz Main/RF & 500 MHz Auxiliary/IF Synthesizer
traditional integer-N synthesizers to build multimode
• Low phase noise -91 dBc/Hz @ 1800 MHz measured inside
the loop bandwidth
or narrowband circuits. Phase noise is often the most
important design consideration. When their requirements
call for a fine step size, designers must divide the reference
CX72301 Specific Performance:
frequency to achieve a lower comparison frequency. This
• Dual 1.0 GHz Main/RF & 500 MHz Auxiliary/IF Synthesizer
problem of low comparison frequency can be avoided
• Low phase noise -96 dBc/Hz @ 950 MHz measured inside
using fractional-N techniques that employ DS technology.
the loop bandwidth
These techniques allow the designer to maintain a
high comparison frequency, which in turn permits low
CX72302 Specific Performance:
phase noise.
• Dual 6.1 GHz Main/RF & 1.0 GHz Auxiliary/IF Synthesizer
• Low phase noise -80 dBc/Hz @ 6.1 GHz measured inside
Radio designers, in order to meet systems specifications,
the loop bandwidth'
must often resort to very narrow loop filter bandwidths.
contributions. Conexant’s fractional-N synthesizers allow
CX74038 Dual Fractional-N/Interger-N
Frequency Synthesizer
designers to lower VCO noise, by widening the loop filter
The Conexant CX74038 2.6 GHz/800 MHz dual frequency
bandwidth. Switching speed is also a primary concern of
synthesizer is a complete, low power synthesizer IC tailored
next generation handset and base station manufacturers.
specifically for portable/battery operation. Housed in a tiny
The larger the loop frequency, the faster the switching speed.
3.5mm x 4.5mm chip scale package (also available in 20-pin
This is done at the cost of increasing the VCO phase noise
TSSOP) the CX74038 fractional-N performance offers low
phase noise and fast settling time necessary for use in next
CX72300/01/02 Dual
Fractional-N Synthesizers
generation handset applications.
The CX7230x synthesizers are ideal for applications that
need low phase noise, fine channel step size and fast
CX74038 features:
switching speeds. Offering performance that meets
• Low power consumption for portable/handset
stringent system requirements for a broad range of
applications, these products are suited for use in next
• Supply voltage as low as 2.6V
generation base stations, tactical radios, test equipment
• Very fast switching speed (sub 100 us)
and instrumentation, satellite receivers and low bit rate
• Step size <5 Hz @ 2.6 GHz
FM/FSK/MSK/GMSK telemetry transmitters (Direct Digital
• Dual 2.6 GHz Main/RF and 800 MHz Auxiliary/
Modulation feature).
IF Synthesizer
Features common to this family are:
• Spur-free operation
• Step size <100 Hz (<400 Hz for -CX72302)
• Very fast switching speed (<100 us)
• On-chip oscillator circuit
• Direct Digital Modulation
• 28-pin TSSOP
© 2001, Conexant Systems, Inc. All Rights Reserved.
General Information:
Conexant and the Conexant logo are trademarks
of Conexant Systems, Inc. Other trademarks are
U.S. and Canada: (800) 854-8099
owned by their respective owners. Although Conexant
International: (949) 483-6996
strives for accuracy in all its publications, this material
Headquarters – Newport Beach
may contain errors or omissions and is subject to
change without notice.
4311 Jamboree Rd, P.O. Box C
Newport Beach, CA 92660-3095
Order# 101181B
Conexant shall not be
liable for any special, indirect, incidental or consequential
damages as a result of its use.