RF Frequency Synthesizers are highly versatile RF frequency sources that are used in laboratories as test instruments to radar and signal intelligence systems as frequency sources. The key differentiation between RF frequency synthesizers and local oscillators or other single frequency sources are that RF Frequency Synthesizers can generate frequencies within a relatively wide range based on a programmable input. Hence, an RF Frequency Synthesizer can typically be used alongside digital control schemes or automation software/hardware for performing automated or programed operation.
This flexibility makes RF frequency synthesizers extremely useful for laboratory testing where a range of input frequencies may be needed, or with modern electronic warfare (EW) system development or testing where modern agile frequency sources can rapidly change frequencies over wide bandwidths. RF Frequency Synthesizers are also used along with frequency conversion hardware (mixers) as variable local oscillator (LO) input, which can be used to upconvert/downconvert a band of frequencies over a variable range.
Main Electrical Performance Parameters of RF Frequency Synthesizers
- Frequency Range
- Load impedance (interconnect impedance)
- Output Power
- Step size in integer mode or fractional mode (resolution)
- Phase lock speed (agility)
- Phase noise
- Spurious
- 2nd harmonic
- Reference frequency
- Reference power (continuous wave)
- Reference phase noise
- Internal reference frequency
- Internal reference accuracy
- Operating DC voltage, current, and power
Depending on the end-use, there may be one of several critical RF frequency synthesizer specifications. The most critical for many common applications are frequency range, output power, phase noise, and spurious/2nd harmonic performance. These figures-of-merit impact the output signal quality directly and may limit a frequency synthesizer’s use in certain applications. For instance, a test and measurement application may require much better signal quality (phase noise, spurious, 2nd harmonic, etc.) than a communications application or a frequency agile radar which may prioritize phase lock speed, step size, and/or output power.
What are the types of frequency synthesizer?
There are two main categories of frequency synthesizers with several types. The two main categories are direct and indirect frequency synthesizers, where both of these categories of frequency synthesizers can either be analog or use digital frequency synthesis (DFS). A Direct frequency synthesizer directly generates a waveform without any frequency transforming elements or with indirect circuitry. An indirect frequency synthesizer uses something like a phase-lock loop (PLL) or other indirect circuitry which replicates a signal using an output oscillator and various types of circuitry.