June 26, 2014 – Linear Technology Korea (Representative Hong Sa-gwak) announced the launch of the LTC6948, a high-performance 6GHz fractional-N phase-locked loop (PLL) circuit with an integrated VCO (voltage-controlled oscillator). The technical core of the LTC6948 is an advanced fourth-order delta-sigma modulator that employs intelligent noise-shaping techniques to minimize noise contribution while eliminating the fractionalization spur phenomenon that appears in most commercially available fractional-N PLLs. The device is provided with overall advantages of the fractionalization process, from frequency agility to overall improved phase noise, and the conventional defects that appear when using fractional-N PLLs do not occur. In other words, the LTC6948 is a fractional-N PLL with integer-N spurious performance where the N value is an integer. These advantages combined with industry-leading 1/f noise and in-band phase noise reduction characteristics make the LTC6948 ideal for demanding wireless, test and measurement, and military applications.

The figure-of-merit, which is an excellent normalized in-band phase noise floor, is important in low phase noise solutions. However, the in-band noise floor is often degraded by the 1/f noise performance of the PLL core. The LTC6948 provides an outstanding -274dBc/Hz normalized 1/f noise specification. This specification does not compromise the excellent 226dBc/Hz normalized in-band phase noise floor. Through integrated specifications, the LTC6948 is suitable for wireless communications using complex modulation circuits, communication systems utilizing long burst times, and applications requiring high SNR such as Doppler radar.

The LTC6948 includes a reference divider, phase frequency detector, ultra-low noise charge pump, fractional divider, VCO output divider, and buffer. By integrating a VCO with all PLL components and competitive phase noise performance, it reduces overall system cost, design complexity, and solution size. The LTC6948 is offered in four versions, each providing different VCO frequency bands with high-speed options delivering up to 6.39GHz. The VCO output divider can be programmed from 1 to 6 to cover frequencies up to 373MHz over a wide range. VCO calibration can be completed in less than 10µs, a faster computational order than many competing products. This characteristic makes the LTC6948 the PLL choice for solutions requiring very short settling times.

The LTC6948 can be easily designed using the FracNWizardTM simulation and design tool, which is available for free download at www.linear.com/FracNWizard. The FracNWizard design tool helps provide appropriate loop filter component values with a single click, reducing complex calculation time for system designers. This design tool accurately predicts PLL performance, supports designers in the debug process, and aids in design decisions.

All versions of the LTC6948 are specified for the full operating junction temperature range of -40°C to 105°C. These products are supplied in a 4mm × 5mm, 28-pin QFN package.

Photo Caption: 6GHz Frac-N PLL with Integrated VCO