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Member

Join Date: Oct 2010
Posts: 6

PIN Diode Switch in a Frequency Multiplier Circuit

10/28/2010 8:37 AM

Hello everyone,

We are using a SP4T PIN diode switch to switch to one of four temperature compensated crystal oscillators with center frequencies in the UHF range. This is passed through a frequency multiplier of multiplication factor 96 and we see the output (96th harmonic) in the X-band (11-12 GHz) through the spectrum analyzer.

The SP4T switch has been causing undesired spectral noise in the output spectrum with temperature testing on the switch( 0 to 50 deg C). One of the possibilities of the noise seemed like the DC block capacitor. But replacing it didn't work.

Any thoughts on what the cause might be?

Thanks.

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Guru

Join Date: Aug 2010
Location: Melbourne, Australia
Posts: 740
Good Answers: 24
#1

Re: PIN Diode Switch in a Frequency Multiplier Circuit

10/31/2010 6:28 PM

Is the spectral noise a result of a step in phase of the output signal cause by the switching?

Do the signals need to be phase synchronised at the point of switching?

Is the switching smooth, ie no dither?

Just some thoughts

Bill

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Join Date: Oct 2010
Posts: 6
#2
In reply to #1

Re: PIN Diode Switch in a Frequency Multiplier Circuit

10/31/2010 7:10 PM

Yes I did consider the phase and thought the capacitors in the arm might be the cause of it. Do you think the composition of the capacitor affects it? We use multilayer ceramic capacitors, but we are going to try and replace them with porcelain ones. But the problem is encountered only in one of the arms out of the four arms in the switch. We tried lowering the switching speed in the problematic arm, it reduced the spikes but did not eliminate it. Thanks.

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Guru

Join Date: Aug 2010
Location: Melbourne, Australia
Posts: 740
Good Answers: 24
#3
In reply to #2

Re: PIN Diode Switch in a Frequency Multiplier Circuit

10/31/2010 10:57 PM

If the problem is occurring in only one arm, there is something different in that arm - a faulty component, a bridge, an impedance mismatch, a wiring error .... perehaps in the switch, or associated components or even the load.... check carefully.

Are you able to try swapping connections, loads, boards etc to see what items the fault follows?

If that is possible, it should narrow down your search considerably.

Regards

Bill

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Member

Join Date: Oct 2010
Posts: 6
#4
In reply to #3

Re: PIN Diode Switch in a Frequency Multiplier Circuit

11/02/2010 11:12 AM

Thank you so much for the help. It looked it was an impedance mismatch and I was able to fix it and the rest was just assembly problem with the epoxy creeping up around the diode in the diode holes that was causing it.

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Guru

Join Date: Aug 2010
Location: Melbourne, Australia
Posts: 740
Good Answers: 24
#5
In reply to #4

Re: PIN Diode Switch in a Frequency Multiplier Circuit

11/02/2010 6:32 PM

I am pleased to be of service.

All the very best

Bill

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