A key feature of the STuW81300 in comparison with much of the competition is the integration of LDO voltage regulators required by the device. This is an important feature because the performance of RF synthesizers can be quite sensitive to noise on the power supplies. If the power supply is not clean, that noise could be reflected in the output frequency from the synthesizer. Consequently many competitive devices require very high-performance voltage regulators in order to supply low noise power rails to the synthesizer in order to obtain the best low-noise output performance. ST has removed that burden from the customer by integrating high performance low-noise LDO voltage regulators in the STuW81300 and the STW81200. The STuW81300 and STW81200 integrate five LDO voltage regulators, one for each of the different portions of the device: the digital section, the analog section, the VCO section, the charge pump and PFD section, and the output section. This allows the STuW81300 and STW81200 to be operated from one external supply, which can be anywhere from 3 V to 5.4 V. The integrated LDO voltage regulators generate all of the voltages need by the device. Of course, some external capacitors are needed for filtering, as would be required by any LDO voltage regulator, but the space requirement and cost of external voltage regulators is saved. The STuW81300 also has a set of low-power functional modes. If power is a concern, the device can be run at lower power and lower voltage, with of some minor trade-offs, such as lower output power levels. The STuW81300 is controllable and configurable via a set of internal registers which can be programmed via an SPI digital bus.