What is an RF Frequency Synthesizer and Applications

RF frequency synthesizer technology is widely used & there are several different types of PLL synthesizers, direct and indirect, digital & analog, etc.

• It is an electronic circuit that generates a range of frequencies from a single reference frequency.
• The frequency synthesizer’s outputs are related to the stability and accuracy of its reference frequency input.
• Therefore the synthesizers use stable and accurate reference frequencies, such as those provided by a crystal oscillator.
• The frequency synthesizer compares the phases of two input signals and produces an error signal that is proportional to the difference between their phases.
• The error signal is then given to low pass filtered and used to drive a VCO then it gives an output frequency.
• The output frequency is going through a frequency divider back to the input of the system, producing a negative feedback loop.
• The output frequency is the drain, then the phase error signal will increase and drive the frequency in the opposite direction so, the error is reduced.
• Therefore, the output is locked to the frequency at the other input.
• This other input is usually derived from a crystal oscillator, which is very stable in frequency and is also called a reference.
• The block diagram below shows the basic elements and arrangement of a PLL-based frequency synthesizer.
• A frequency synthesizer is the ability to generate multiple frequencies is the divider placed between the output and the feedback input.

• This is usually in the form of a digital counter, with the output signal acting as a clock signal.
• It is digital, is very easy to interface to other digital components or a microprocessor and this circuit is straightforward to implement using flip-flops.
• It allows the frequency output by the synthesizer to be easily controlled by a digital system.

Applications of Frequency Synthesizer

• This synthesizer is used in many devices like radio receivers, televisions, mobile telephones, radiotelephones, walkie-talkies, CB radios, cable television converter boxes, satellite receivers, and GPS systems.
• The techniques used in frequency synthesizers are frequency multiplication, frequency division, direct digital synthesis, frequency mixing, and in PLLs to generate its frequencies.