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Amplitude/Phase transient Measurement - High Speed/High Accuracy

Question asked by mikejvir- on Sep 4, 2015
Latest reply on Sep 25, 2015 by Dr_joel
Hello All,

This might not be the best forum, but I figure I would start here. If there is a way to cross post to the spectrum analyzer and oscilloscope forums that would be great.

Task

I have been task with measuring the switching time of a digital attenuator to within 0.1 dB and 1 degree of the final value and the expected time is 30 ns.  The frequencies are 1 to 3 GHz.  The attenuator is a 2 bit 6 dB step (18 dB total).  At 1 GHz the phase delta is less than 1 degree and at 3 GHz it is about 5 degrees /  step.

PNA-X
I looked into this, but even with the IF BW wide open in CW mode, I can not get the time resolution. This would be perfect because I could do a response calibration and get both amplitude and phase simultaneously.  

*Amplitude*
_Power Sensor_ (U2021XA) are not good since they do not the time resolution.
_Crystal Detector_ saw about 55 mV for 18 dB or I would need a step of 0.03 mV step for the oscilloscope.  Unfortunately the oscilloscope I have access to is over 10 years old (non Agilent) and yields 10 times that for a error term.
_Spectrum Analyzer_ (Non Agilent) had 50 MHz resolution BW but the timing was way off.
I had to settle on using the oscilloscope directly since it was digital and had a 50 ohm input. Data was sampled at 10 GS/s.  In the reference state (0 dB) I maximized the voltage on the screen.  It did not have a envelope function, so I just use the maximum function.  I also am doing a 400 point running averaging on the maximum data to "smooth" it.  It seems reasonable and the customer is happy, but I am not since I typically see 0.1 dB ripple on the smoothed data.

*Phase*
Very limited here.  I put together a discriminator.  I split the source.  One path has the line stretcher and goes into the LO port of a double balance mixer.  The other port goes into a variable attenuator, the device under test and into the RF port of the mixer.   The IF port has a low pass filter with at least 80 dB of reject at the frequency of interest.  Here I have been finding all sorts of little issues that are much to long to go into.  I am looking into a getting a phase detector from Holzworth Instrument to see if this helps with some of my issues.

Been thinking about VSA and the new Infiniium S-Series (10 bit A/D).

So I am looking for any inputs to get the high accuracy and timing.

Thanks for any advice in advance.


Michael Virostko
Integrated Device Technology  

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