DATA SHEET
CX72301: Spur-Free, 1.0 GHz Dual Fractional-N Frequency
Synthesizer
synthesizer is a key building block for high-performance radio
Applications
system designs that require low power and fine step size.
• General purpose RF systems
The ultra-fine step size of less than 100 Hz allows this synthesizer
• Low bit rate wireless telemetry
to be used in very narrowband wireless applications. With proper
• Instrumentation
temperature sensing or through control channels, the
synthesizer’s fine step size can compensate for crystal oscillator
or Intermediate Frequency (IF) filter drift. As a result, crystal
oscillators or crystals can replace temperature- compensated or
ovenized crystal oscillators, reducing parts count and associated
component cost. The device’s fine step size can also be used for
Doppler shift corrections.
• Specialized Mobile Radios (SMRs) and Private Mobile Radios
(PMRs)
Features
• Spur-free operation
The CX72301 has a phase noise floor of –95 dBc/Hz up to
1.0 GHz operation as measured inside the loop bandwidth. This is
permitted by the on-chip low noise dividers and low divide ratios
provided by the device’s high fractionality.
• 1.0 GHz maximum operating frequency
• 500 MHz maximum auxiliary synthesizer
• Ultra-small step size, 100 Hz or less
Reference crystals or oscillators up to 50 MHz can be used with
the CX72301. The crystal frequency is divided down by
independent programmable divider ratios of 1 to 32 for the main
and auxiliary synthesizers. The phase detectors can operate at a
maximum speed of 25 MHz, which allows better phase noise due
to the lower division value. With a high reference frequency, the
loop bandwidths can also be increased. Larger loop bandwidths
improve the settling times and reduce in-band phase noise.
Therefore, typical switching times of less than 100 µs can be
achieved. The lower in-band phase noise also permits the use of
lower cost Voltage Controlled Oscillators (VCOs) in customer
applications.
• High internal reference frequency enables large loop bandwidth
implementations
• Very fast switching speed (e.g., below 100 µs)
• Phase noise to –96 dBc/Hz inside the loop filter bandwidth
@ 950 MHz
• Software programmable power-down modes
• High-speed serial interface up to 100 Mbps
• Three-wire programming
• Programmable division ratios on reference frequency
• Phase detectors with programmable gain provide a
programmable loop bandwidth
The CX72301 has a frequency power steering circuit that helps
the loop filter steer the VCO when the frequency is too fast or too
slow, further enhancing acquisition time.
• Frequency power steering further enhances rapid acquistion
time
The unit operates with a three-wire, high-speed serial interface. A
combination of a large bandwidth, fine resolution, and the three-
wire, high-speed serial interface allows for a direct frequency
modulation of the VCO. This supports any continuous phase,
constant envelope modulation scheme such as Frequency
Modulation (FM), Frequency Shift Keying (FSK), Minimum Shift
Keying (MSK), or Gaussian Minimum Shift Keying (GMSK). This
capability can eliminate the need for In-Phase and Quadrature
(I/Q) Digital-To-Analog Converters (DACs), quadrature
upconverters, and IF filters from the transmitter portion of the
radio system.
• On-chip crystal oscillator
• Frequency adjust for temperature compensation
• Direct digital modulation
• 3 V operation
• 5 V output to loop filter
• 28-pin EP-TSSOP 6.4 x 9.7 mm package
Description
Skyworks CX72301 direct digital modulation fractional-N
frequency synthesizer provides ultra-fine frequency resolution,
fast switching speed, and low phase-noise performance. This
Figure 1 shows a functional block diagram for the CX72301. The
device package and pinout for the 28-pin Exposed Pad Thin
Shrink Small Outline Package (EP-TSSOP) are shown in Figure 2.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
101090H • Skyworks Proprietary and Confidential information • Products and Product Information are Subject to Change Without Notice • July 21, 2004
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