This results in a device with the full benefits of fractionalisation— from frequency agility to overall improved phase noise — but without the traditional drawbacks of using a fractional-N PLL. The LTC6948 is a fractional-N PLL with integer-N spurious performance. Pairing these benefits with industry-leading 1/f noise and reduced in-band phase noise, makes the PLL ideal for demanding wireless, test and measurement, and military applications.
A good normalised in-band phase noise floor, or figure-of-merit, is important for a low phase noise solution. However, in-band noise floor is often corrupted by the 1/f noise performance of the PLL core. The LTC6948 has a -274 dBc/Hz normalised 1/f noise specification that does not hinder its outstanding -226 dBc/Hz normalized in-band phase noise floor. These combined specifications make the LTC6948 applicable to applications that demand a high SNR, such as wireless communications using complex modulation schemes, communications systems that employ long burst durations and Doppler radar.
The LTC6948 reduces overall system cost, design complexity and solution size by integrating a VCO with competitive phase noise performance and all PLL components, including a reference divider, phase-frequency detector, ultralow noise charge pump, fractional divider and VCO output divider and buffer. There are four versions of the LTC6948, each offering a different VCO frequency band with the fastest option delivering up to 6.39 GHz. The VCO output divider can be programmed from 1 through 6 to cover a wide range of frequencies down to 373 MHz. VCO calibration is typically completed in a little over 10 µs, an order of magnitude faster than many competing parts.
Designing with the LTC6948 is done with the FracNWizard simulation and design tool, available for free download at www.linear.com/FracNWizard — the FracNWizard design tool helps provide appropriate loop filter component values with a click of a button, saving the system designer hours of complex calculations. It accurately predicts PLL performance, assisting the designer in the debugging process and in making