Synthesizer frequency stability

[karote]

frequency stability of synthesizer

Hi all,

Does the long term frequency stability of a synthesizer depend on completely of the accyracy and stability of the PLL reference frequency? So that the loop filter design and the VCO itself does not affect on the long term stability (it is assumed that the VCO will meet the tuning capabilities at all times)

 

[RFDave]

frequency stability synthesizer

Long term frequency accuracy (Things specified like PPM Offset) are, to first order, entirely determined by the reference oscillator. If you are using a fractional N synthesizer, the DSM bit width accuracy can contribute a fixed frequency offset.

Short term frequency accuracy (Phase Noise or jitter) is determined by the oscillator performance.

Dave
www.keystoneradio.com

 

[jecyhale]

vco stability determined reference

Hi all,

Does the long term frequency stability of a synthesizer depend on completely of the accyracy and stability of the PLL reference frequency? So that the loop filter design and the VCO itself does not affect on the long term stability (it is assumed that the VCO will meet the tuning capabilities at all times)

Of course affect. the bandwidth is most improtant for affecting the term satblility.

 

[sergio mariotti]

synthesizer frequency stability

I agree that the most important is due to the Reference Stability.

A very small effect on the phase drift of the out signal, may be added by a drift on the electrical lenght of the loop. A temperature change produce a lenght change so a phase change.
In my experience, i've seen that very small effect on a 32 GHz PLO.

That kind of effect may be measured with a methodology called "Allan Variance"

 

[biff44]

frequency accuracy vs frequency stability

In many cases today, the crystal frequency reference +/- ppm drift is the same as the transmitter frequency drift in ppm.

In older designs, such as FSK systems where the modulation is AC summed with the PLL control signal, then for certain data streams you can have an apparent frequency walk off of the desired frequency. This is primarily a problem if there is no randomizer used in the digital data, or if there are long periods of the same bit transmitted.

 

[dinesh agarwal]

loop filter design defenitely effect the stability of synthesiser.

actually it control the stabilily factor of synthesiser, bandwidth, settlingsime and ofcourse damping factor

loop bandwidth also effect the output noise of synthesiser.