Frequency synthesizers generate discrete frequencies with crystal stability. They have become an integral part of advanced communication systems in general and wireless communication systems in particular. They substituted the the old mechanical and electromagnetic tuners.
In this forum it is required to discuss the performance parameters of such devices and the advancements in their implementation.
The following are some of the parameters in (http://grouper.ieee.org/groups/802/16/tg1/contrib/802161c-00_04.pdf) for frequency synthesizers that are used in testing communications systems at 30GHz.:
* Frequency range in GHz.
* Frequency raster MHz/ Raster offset MHz
* Tx/Rx switching time/accuracy.
* Switching time from upstream to downstream * frequency range (important for half-duplex terminals)
* Channel switching time/accuracy .
* Power output dBm
* Harmonics suppression dBc.
* Spurious response dBc
* Single Side Band Phase Noise dBc/Hz
* Noise Floor dBc
* Integrated phase noise dB (Total), ..............Thanks. @AlDmour
Dear colleagues, in spite of the importance of this topic for the advanced communication systems i observed two things:
the first one , one of the researchgate members down voted my question. This is not a moral act.
the second is that very few colleagues shared with comments on the topic.
I would like to thank them for their contribution. Thank you Ismat, thank you Vasile.
Now, i will try to concentrate and order the answer of the colleagues.
From the basic definition the frequency synthesizer is a discrete frequency generator with crystal stability. So, all performance parameters of the frequency generators are inherited by the frequency synthesizes, These parameters are treated in an a previous question on researchgate:https://www.researchgate.net/post/What_are_the_full_characteristics_of_a_frequency_generator_and_how_are_they_measure.
Here the frequency synthesizer generates a sinusoidal waveform. The performance parameters are:
- The maximum amplitude of the generated voltage
- The amplitude stability
-The generated frequency range from fmin to fmax.
- The frequency step
-The source impedance.
-The spectral purity and nonlinear distortion
-The spurious responses
-Long term Frequency stability
- Short term frequency stability, the phase noise
- Settling time for switching from one discrete frequency to the other.
-Noise floor
Thank you
Three things prmarily rate a synthesizer: (1) phase noise (2) switching speed and (2) frequency step size.
Most important parameters in a synthesizer are:
1- Jitter (or phase noise)
2- Lock time
3-Frequency steps and accuracy
4- Speed (or ability to work in higher frequencies)
5- power consumption
6-chip area
The lock time is typically specified as the time required for the output frequency to reach within a certain margin (e.g: 100 ppm) around its final value.
Lock times in RF systems vary from a few tens of msec to a few tens of µsec (for ultra-wideband systems need to be less than 10nsec).
In PLLs or DLLs you can see the control voltage to calculate the lock time or you can use output signal (the time in which DLL or PLL is near lock)
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