AD2 network analyser frequency

[danny014789]

Dear all, 

 

I bought in the AD2 hoping to use it as a network analyser to plot a smith chart.

From the reference centre (https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/start?redirect=1)I note that the network analyser can go up to 25MHz? (On the right hand chart, it states Frequency Sweep Range: 1mHz to 10/25MHz)

 

However on waveform software I could only select up to 10MHz, could anyone suggest how to set the upper limit to 25MHz? The interested frequency is 13.56MHz.

 

Best Regards

Danny Chen

[attila]

Hi @danny014789

In the currently released WF version 2.12.2 in Network Analyzer, under Wavegen gear select Frequency Extended
In the latest WF beta version (release candidate 3.13.23) this limitation is removed, it lets you set it up to 25MHz or 50MHz with external signal:
https://forum.digilentinc.com/topic/8908-waveforms-beta-download/

 

[danny014789]

Thank you for your prompt respond. 

 

I have another question, RF measurements are new to me, would it be possible to measure or calculate the impedance of DUT from the network analyzer function? The application environment makes it difficult to connect to an external reference resistor that is required for the impedance analyzer function.

 

Best

Danny Chen

[attila]

Hi @danny014789

In order to measure the impedance a reference resistor is required.

From the Impedance Analyzer module or similar circuit it is suffice to bring two wires to the DUT. I use this method to verify components on PCAs.
For such in-circuit testing low voltages and offset should be used, like 0.1-0.5V amp and offset, to not to interfere with the silicon, diodes, ICs

In Network Analyzer under Custom One/Two custom measurements can be created, but such IA function are available in the IA interface with more options, compensation...

 

[danny014789]

Hi Attila

 

Thanks for your reply, as you suggested I tried out the impedance analyser but with the BNC extension board rather than the impedance analyser extension board (Bought it but not with me yet).

 

I did compensations as you mentioned and tried using both 100 ohm and 1kohm as the reference resistors, however the results were different, I am wondering how do you chose the right reference resistor? I am measuring an plasma source antenna impedance and has very little idea on the impedance of it.

1 kOhm:

 

100 Ohm:

 

Thanks!

Danny Chen

[attila]

Hi @danny014789

Have you changed the Resistor value in the interface too? The measurements are calculated based on this value.

The probe impedance together with the reference resistor and DUT changes the resonance points, since all these are complex RLC circuits.
The DUT may have different characteristics based on the current, which is limited by the reference resistor. 

Here you can see an inductor for which at high frequencies the capacitance dominates.

 

[danny014789]

Yes, I have changed the resistor value in the interface, I would make a known impedance DUT to test later in the week.. thanks