PS6500

The PS6500 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 in designing high-performance narrowband and multi-band radio systems that require low power and fine step size.

The ultra-fine step size of less than 400 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 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 PS6500's fine step size can also be used for doppler shift corrections.

The PS6500 has a phase noise floor of -80 dBc/Hz up to 6.5 GHz operation.This is permitted by the on-chip low noise prescalers and low divide ratios provided by the IC's high fractionality.

Reference crystals or oscillators up to 50 MHz can be used with the PS6500.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, permitting 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. Typical switching times of less than 100 ms can thus be achieved with a 10 MHz reference. The PS6500's lower in-band phase noise also permits the use of lower cost Voltage Controlled Oscillators (VCOs) in customer applications.

The PS6500 has a Frequency Power SteeringTM circuit (patent pending), that assists the loop filter to steer the VCO when the frequency is too fast or too slow. In this configuration, acquisition times of up to five times faster than
conventional phase/frequency detectors can be achieved.

The unit operates with a 3-wire, high-speed serial interface. A combination of a large bandwidth, fine resolution, and the 3-wire, high-speed serial interface allows for a direct phase and frequency modulation of the VCO. PS6500 supports any constant envelope and continuous phase modulation which means any analog FM or digital FM. This capability can eliminate the need for I & Q DACs, quadrature upconverters, and IF filters from the transmitter portion of the radio system.1