biff44
Joined: 24 Dec 2004
Posts: 1838
Helped: 244
Location: New England, USA
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 23 Oct 2009 21:40 Re: Microphonic problem in Frequency Synthesizer unit |
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Don't vibrate it!
Failing that, I would try to isolate WHY it has increased phase noise under vibration.
Most frequency synthesizers use a stable low frequency oscillator (such as a 10 MHz crystal oscillator) to generate higher frequencies. They do this in various ways, such as using phase locked loops, etc. But the net effect is that that 10 MHz frequency standard gets "multiplied" up to several GHz. So if the frequency standard has noise under vibration, the noise at the higher frequency will be 100's to 1000's of times worse. So I would try to improve the frequency standard's stability. Maybe buy a better one to use externally, or mount it on rubber flexible stand-offs to reduce some of the vibration.
There can be many other reasons, though. A cover can be moving mechanically, which is pulling a VCO frequency, and the PLL does not have sufficient open loop gain to compensate. You would want to stiffen such a cover to vibrate less.
There could be a poor connection, like between a substrate and a housing ground, and mechanical vibration is making/breaking the ground contact--thereby causing big jumps in VCO frequency. You would want to fix this poor mechanical design to allow sufficient stress relief.
You could have a loose comonent, like a coil or wire inside of a VCO, that is moving under vibration, and causing frequency modulation.
And on and on.
Rich
Maguffin Microwave LLC
www.MaguffinMicrowave.com
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