Skyworks SKY72300-21 direct digital modulation fractional-N frequency synthesizer provides ultra-fine frequency resolution, fast switching speed, and low phase-noise performance. This synthesizer is a key building block for high-performance radio system designs that require low power and fine step size. The ultra-fine step size of less than 100 Hz allows this synthesizer to be used in very narrowband wireless applications. With proper temperature sensing or through control channels, the synthesizer’s fine step size can compensate for crystal oscillator or Intermediate Frequency (IF) filter drift. As a result, crystal oscillators or crystals can replace temperature-compensated or ovenized crystal oscillators, reducing parts count and associated component cost. The device’s fine step size can also be used for Doppler shift corrections. The SKY72300-21 has a phase noise floor of –90 dBc/Hz up to 2.1 GHz operation as measured inside the loop bandwidth. This is permitted by the on-chip low noise dividers and low divide ratios provided by the device’s high fractionality. Reference crystals or oscillators up to 50 MHz can be used with the SKY72300-21. The crystal frequency is divided down by independent programmable dividers (1 to 32) for the main and auxiliary synthesizers. The phase detectors can operate at a maximum speed of 25 MHz, which allows better phase noise due to the lower division value. With a high reference frequency, the loop bandwidths can also be increased. Larger loop bandwidths improve the settling times and reduce in-band phase noise. Therefore, typical switching times of less than 100 s can be achieved. The lower in-band phase noise also permits the use of lower cost Voltage Controlled Oscillators (VCOs) in customer applications. The SKY72300-21 has a frequency power steering circuit that helps the loop filter to steer the VCO when the frequency is too fast or too slow, further enhancing acquisition time. The unit operates with a three-wire, high-speed serial interface. A combination of large bandwidth, fine resolution, and the threewire, high-speed serial interface allows for a direct frequency modulation of the VCO. This supports any continuous phase, constant envelope modulation scheme such as Frequency Modulation (FM), Frequency Shift Keying (FSK), Minimum Shift Keying (MSK), or Gaussian Minimum Shift Keying (GMSK). This capability can eliminate the need for In-phase and Quadrature (I/Q) Digital-to-Analog Converters (DACs), quadrature upconverters, and IF filters from the transmitter portion of the radio system.