PLL frequency synthesizers are electronic devices that produce frequencies coherent to a reference frequency. They use phase-locked loops (PLLs), electronic circuits that consist of a phase/frequency detector (PFD), low pass filter, and voltage-controlled oscillator (VCO). PLL frequency synthesizers use the PFD to compare a feedback frequency with a divided-down version of the reference frequency. Integral PLL frequency synthesizers divide the output frequency by an integer. Fractional PLL frequency synthesizers divide the output frequency by a non-integer. With both types of devices, the PFD’s output (current pulses) are filtered and integrated to generate a voltage. In turn, this voltage drives the VCO to increase or decrease the output frequency, moving the PFD’s average output towards zero. Sensitivity varies over the full VCO frequency range. Input reference counters are used to reduce the reference input frequency. Feedback counters are used to reduce the output frequency for comparison with the scaled reference frequency. Applications for PLL frequency synthesizers include wireless base stations, mobile hand sets, personal digital assistants (PDAs), broadband wireless access, satellite communications, and local area networks (LANs).

Selecting PLL frequency synthesizers requires an analysis of performance specifications such as frequency range, step size, settling time, output power, and voltage standing wave ratio (VSWR) vs. return loss. Frequency range is the range of frequencies that PLL frequency synthesizers can generate. Step size is the minimum output frequency that devices can achieve. Settling time is the maximum amount of time needed for the output signal to reach its final, stable state. Output power is usually measured in decibels per meter (dBm) for a 50 W load. Additional considerations include phase noise, reference spurs, and lock time. Phase noise is the ratio of the carrier power to the power found in a 1 Hz bandwidth at a defined frequency, usually 1 kHz. Reference spurs are artifacts at discrete offset frequencies generated by internal counters and charge pump operation at the PFD frequency. Lock time is the time needed to jump from one specified frequency to another specified frequency within a given frequency tolerance.  

PLL frequency synthesizers are electronic devices that produce frequencies coherent to a reference frequency. They use phase-locked loops (PLLs), electronic circuits that consist of a phase/frequency detector (PFD), low pass filter, and voltage-controlled oscillator (VCO). PLL frequency synthesizers use the PFD to compare a feedback frequency with a divided-down version of the reference frequency. Integral PLL frequency synthesizers divide the output frequency by an integer. Fractional PLL frequency synthesizers divide the output frequency by a non-integer. With both types of devices, the PFD’s output (current pulses) are filtered and integrated to generate a voltage. In turn, this voltage drives the VCO to increase or decrease the output frequency, moving the PFD’s average output towards zero. Sensitivity varies over the full VCO frequency range. Input reference counters are used to reduce the reference input frequency. Feedback counters are used to reduce the output frequency for comparison with the scaled reference frequency. Applications for PLL frequency synthesizers include wireless base stations, mobile hand sets, personal digital assistants (PDAs), broadband wireless access, satellite communications, and local area networks (LANs).

Selecting PLL frequency synthesizers requires an analysis of performance specifications such as frequency range, step size, settling time, output power, and voltage standing wave ratio (VSWR) vs. return loss. Frequency range is the range of frequencies that PLL frequency synthesizers can generate. Step size is the minimum output frequency that devices can achieve. Settling time is the maximum amount of time needed for the output signal to reach its final, stable state. Output power is usually measured in decibels per meter (dBm) for a 50 W load. Additional considerations include phase noise, reference spurs, and lock time. Phase noise is the ratio of the carrier power to the power found in a 1 Hz bandwidth at a defined frequency, usually 1 kHz. Reference spurs are artifacts at discrete offset frequencies generated by internal counters and charge pump operation at the PFD frequency. Lock time is the time needed to jump from one specified frequency to another specified frequency within a given frequency tolerance.  

There are several package types for PLL frequency synthesizers. Surface mount technology (SMT) adds components to a printed circuit board (PCB) by soldering component leads or terminals to the top surface of the board. Through hole technology (THT) mounts components by inserting component leads through holes in the board and then soldering the leads in place on the opposite side of the board. PLL frequency synthesizers that use flat packaging (FPAK) are also available. Connectorized devices attach with coaxial or other types of connectors. Waveguide assemblies consist of a hollow metallic conductor with a rectangular, elliptical, or circular cross-section. Some conductors contain solid or gaseous dielectric materials. 

PLL frequency synthesizers use several types of connectors. Bayonet Neil-Concelman (BNC) connectors are used in applications to 2 GHz. Threaded Neil-Concelman (TNC) connectors are similar in size to BNC connectors, but feature a threaded coupling nut for applications that require performance to 11 GHz. Miniature coaxial (MCX) connectors provide broadband capability through 6 GHz and are used in applications where weight and physical space are limited. Ultra high frequency (UHF) connectors are designed with non-constant impedance for use in comparatively low voltage and low frequency applications. Subminiature-A (SMA) connectors directly interface the cable dielectric without air gaps. Subminiature-B (SMB) connectors snap into place and are used for frequencies from DC to 4 GHz. Subminiature-P (SMP) connectors are rated to 40 GHz and, depending on the detent type, can withstand from 100 to 100,000 interconnect cycles. Other connectors for PLL frequency synthesizers include MMCX, Mini-UHF, Type F, Type N, 1.6/5.6, and 7-16 connectors.