Low Power Synthesizer from TI

June 22, 2015 | 01:30
The LMX2571 synthesizer chip
The LMX2571 synthesizer chip
The LMX2571 from Texas Instruments is a low-power, high-performance, wideband PLLatinum RF synthesizer that integrates a delta-sigma fractional N PLL, multiple core voltage-controlled oscillator (VCO), programmable output dividers and two output buffers. The VCO cores work up to 5.376 GHz resulting in continuous output frequency range from 10 MHz to 1344 MHz.

A dedicated 5 V charge pump and output divider also allows the synthesizer to be used together with an external VCO. A novel programmable multiplier is incorporated to help improve spurs, allowing the system to use every channel even if it falls on an integer boundary. The output has an integrated SPDT switch that can be used as a transmit/receive switch in FDD radio application. Both outputs can also be turned on to provide 2 outputs at the same time.

The LMX2571 supports direct digital FSK modulation through programming or pins. Discrete level FSK, pulse shaping FSK, and analog FM modulation are supported. A new FastLock technique can be used which allows the user to step from one frequency to the next in less then 1.5 ms even when an external VCO is used with a narrow band loop filter.

Key Features of the LMX2571:
• Any Frequency from 10 MHz to 1344 MHz
• Low phase noise and spurs
o –123 dBc/Hz at 12.5 kHz offset @ 480 MHz o –145 dBc/Hz at 1 MHz offset @ 480 MHz
o Normalized PLL noise floor of –231 dBc/Hz
o Spurious better than –75 dBc/Hz
• New FastLock reduces lock time
• A novel technique to remove integer boundary spurs
• Integrated 5 V charge pump and output divider for external VCO operation
• 2, 4 and 8 level or arbitrary level direct digital FSK modulation
• One TX/RX output or two fanout outputs
• Crystal, XO or differential reference clock input
• Low current consumption
o 39 mA typical synthesizer mode (Int. VCO)
o 9 mA typical PLL mode (Ext. VCO)
• 24 Bit fractional-N Delta Sigma modulator

The LMX2571 is available in a 6 mm square quad flat no-leads (QNF) package for US$5.50 per unit in 1,000 unit quantities. The LMX2571 is also supported by the LMX2571EVM evaluation board available for US$249 from authorized TI distributors.
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