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Amplitude/Phase transient Measurement - High Speed/High Accuracy

Question asked by mikejvir- on Sep 13, 2015
Latest reply on Sep 14, 2015 by algoss
Hello All,

This might not be the best forum, but I started in the network analyzer application forum with no replies so I am reposting here.

+_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.
_Oscilloscope_ 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.  It is even worse when I am in the 18 dB state.

+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). (Ideas?)

Also, thinking of using a oscilloscope directly and taking the mixer out.  Take the two signals and go directly into the oscilloscope.  Adjust the line stretcher for identical zero crossing. Since the frequency is known I could calculated the phase offset (time).  Amplitude can be done also.

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

Thanks for any advice in advance.

Michael Virostko
Integrated Device Technology  

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