Frequency synthesizer achieves a closed-loop phase noise of -100dBc/Hz

Linear Technology’s LTC6946 integer-N frequency synthesizer integrates a VCO and delivers -226dBc/Hz normalized, closed-loop, in-band phase noise; -274dBc/Hz normalized, in-band flicker noise; and 103dB spurious output. In a typical 900MHz system, these features enable the device to achieve a closed-loop phase noise of -100dBc/Hz at a 1kHz offset.

The device is available in three versions: The LTC6946-1, LTC6946-2, and LTC6946-3 have frequency ranges of 2.24-3.74GHz, 3.08-4.91GHz, and 3.84-5.79GHz, respectively. Each device has an on-chip output divider that is programmable from one through six to extend frequency coverage to as low as 373MHz.

The device integrates a low-noise, 5.7GHz PLL, which includes a reference divider, a phase frequency detector with a phase locked indicator, an ultra-low noise charge pump, and an integer-feedback divider to achieve low-noise PLL operation. The PLL circuit tightly couples to a lownoise VCO and to internal self-calibration to ensure optimum VCO-resonant tuning. The VCO requires no external components. An on-chip SPI-compatible, bi-directional port allows frequency tuning and control and read-back of register and loop-status information.

The frequency synthesizer enhances the performance of multiband base stations supporting LTE, CDMA, WCDMA, UMTS, GSM-communications, and WiMax standards. The device suits use in point-to-point broadband wireless-access, military, avionics and test-and-measurement applications.

The PC-based PLLWizard design-tool software is available to facilitate interactive control and interface with the LTC6946’s evaluation board. Designers can download the tool from the company’s website, and use it to perform simulations and optimization and then interactively verify their designs on a demonstration circuit. All versions of the LTC6946 operate at −40 to +105°C and are available in 4 × 5mm, 28-lead, plastic QFN packages. Prices start at $5.75 (1,000).

Linear Technology