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Ultralow Noise and Spurs 373 to 5790 MHz Integer-N Synthesizers

December 8, 2011
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Linear Tech product LTC6946Linear Technology has developed the LTC6946, the first device in a family of high performance integer-N frequency synthesizers with integrated VCO, delivering −226 dBc/Hz normalized closed-loop in-band phase noise, −274 dBc/Hz normalized in-band 1/f noise and best-in-class −103 dBc spurious output. In a typical 900 MHz application, these performance attributes help to achieve a closed-loop phase noise of −100 dBc/Hz at 1 kHz offset. The device is available in three frequency options: the LTC6946-1 tunes from 2.240 to 3.740 GHz; the LTC6946-2 from 3.080 to 4.910 GHz; and the LTC6946-3 from 3.840 to 5.790 GHz. In addition, each part has an on-chip output divider that is programmable from 1 through 6 to extend frequency coverage to as low as 373 MHz.

This family of devices integrates a low noise 5.7 GHz phase-locked loop (PLL), which includes a reference divider, phase-frequency detector (PFD) with phase-locked indicator, ultralow noise charge pump, and integer feedback divider to attain very low noise PLL operation. The PLL circuit is tightly coupled to a low noise VCO as well as internal self-calibration to ensure optimum VCO resonator tuning for best phase noise performance. The VCO requires no external components. The on-chip SPI compatible bidirectional serial port allows frequency tuning and control, and read back of register and loop status information. All versions of the LTC6946 are specified over the full case temperature range from −40° to 105°C. The products are available in a 4 × 5 mm, 28-lead plastic QFN package.

The low phase noise and spurious capabilities of this family of frequency synthesizers enhance the performance of multiband base stations supporting LTE, W-CDMA, UMTS, CDMA, GSM and WiMAX standards. Its high frequency capability also supports point-to-point broadband wireless access, military, avionics, and high performance test and measurement applications.

Linear Technology,
Milpitas, CA (408) 432-1900,
www.linear.com

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