Pierre Posted May 21, 2020 Share Posted May 21, 2020 Hello, I just discovered Analog Discovery 2...today and I'm very interested in impedance measurements capabilities. I would like to perform capacitance measurements of semiconductors to characterize them. Therefore I need to operate under AC small amplitude level (about 20mV) and under sweeping DC voltage (range of a few volts, say -4V to +1V). So I have at least 3 questions : - Is that kind of measurement record possible with this device ? Specific program needed ? - Should I use the internal generator with some signal attenuation or use an external (fixed frequency) generator ? - Other potential problems to take care of (concerning calibration for instance) ? Many thanks. Pierre. P.S : I would like to perform I/V measurements as well but that should not be a problem I guess... Link to comment Share on other sites More sharing options...
attila Posted May 28, 2020 Share Posted May 28, 2020 Hi @Pierre There is a bit more noise probably because different frequency was used, 10k-100kHz. The reference resistor is also different. The averaging is applied on the measurement, gain/phase. There is no averaging in time view. Link to comment Share on other sites More sharing options...
attila Posted July 20, 2020 Share Posted July 20, 2020 Hi @Pierre You can find the Time view under the View menu. Link to comment Share on other sites More sharing options...
Pierre Posted July 18, 2020 Author Share Posted July 18, 2020 Hi Attila, I'm OK with displaying the impedance and capacitance windows now, but I still can't find the window labelled "Time" that displays the generator voltage (in your messages of 24 and 25th of May)... Link to comment Share on other sites More sharing options...
attila Posted July 13, 2020 Share Posted July 13, 2020 Hi @Pierre You can open various predefined plots and you have two custom plots where you select measurements or custom functions using these. Link to comment Share on other sites More sharing options...
Pierre Posted July 11, 2020 Author Share Posted July 11, 2020 Hi @Attila I'm just trying to use last WF beta version in demo mode, it seems to be OK to get an overview of capacitance measurements. How do you display the window that shows both capacitance and current measurement resistance (noisy) voltages ? Is it also possible to display the capa loss resistance value (Rs if Cs is selected or Rp if Cp is selected) as for any impedance meter ? Link to comment Share on other sites More sharing options...
attila Posted July 6, 2020 Share Posted July 6, 2020 Hi @Pierre The sweep time depends on multiple factors: - Samples: sweep steps/points - Average and Options/Averaging: time and number of measurements - Options/Settle: time - Options/Min Periods: the minimum number of signal periods to capture - one step takes at least about 10ms Sweep time = Samples x max ( ~10ms , Settle + max ( Average , Averaging x MinPeriods / Frequency ) ) Link to comment Share on other sites More sharing options...
Pierre Posted July 5, 2020 Author Share Posted July 5, 2020 Another thing I did not get is the voltage sweep time : how do you set it and what did you chose fo those measurements ? Link to comment Share on other sites More sharing options...
attila Posted May 28, 2020 Share Posted May 28, 2020 Hi @Pierre Yes, you are right, in the second is from 1V to -4V Link to comment Share on other sites More sharing options...
Pierre Posted May 28, 2020 Author Share Posted May 28, 2020 Hello @attila OK, that's clear concerning the noise. But I still don't understand well the capacitance evolution with voltage... maybe it is a +1V / - 4V sweep rather than -4 to +1V ? High capacitance value at start may be explained by diode conduction (around 0.5-1V). This value dos not make sense but is due to low diode resistance -> high current. Then capacitance value should not move in the 0 to 4V range -> voltage sweep seems to be reversed from -4 to +1V to +1V / - 4V. Link to comment Share on other sites More sharing options...
Pierre Posted May 26, 2020 Author Share Posted May 26, 2020 Thank you for your interesting measurement. It seems to be a beautiful tool... There seems to be more signal noise : I suppose because there's less averaging than for first measurement (I see 100ms averaging vs. 500ms for 1st measurement) ? But what I don't understand is the measured value in DC sweep around -4V : why is it so disturbed ? There were not such a pb with 39 pF capacitance measurement... Link to comment Share on other sites More sharing options...
attila Posted May 25, 2020 Share Posted May 25, 2020 Hi @Pierre A 10nF in parallel with a diode looks like this with -4V to +1V offset sweep C1 (yellow in time view) is on AWG 20mV 40mVpp C2 (blue in time view) is on reference resistor Link to comment Share on other sites More sharing options...
Pierre Posted May 24, 2020 Author Share Posted May 24, 2020 Not bad at all... thanks again for the demo. It seems to me you used slightly DC shifted signal and 20mVpp (peak-to-peak) signal (amplitude setting is pp then). I should use 20mVp (peak) signal, which means 40mVpeak-to peak signal -> I should get better signal from this point of view. But the capacitances I intend to measure should be closer to 1-10nF (large diodes characterisation) with measurement frequencies ranging from 1kHz to 1MHz -> capacitance voltage will be weaker. So if you have such a capacitance as a test in your lab, that's worth to try... By the way, if I had to use op-amp devices, how to use it and calibrate the analyser consequently ? Link to comment Share on other sites More sharing options...
attila Posted May 24, 2020 Share Posted May 24, 2020 Hi @Pierre The Scope input resolution is ~300uV (at high gain 5V pk2pk) and the Wavegen output ~180uV (at low gain 2V pk2pk) I don't think you will need, but theoretically you can use external amplifiers. Here you can see the measurement on a 39pF capacitor. The signal is noisy but the IA uses FFT which highly reduces the effect of noise on measurement and you can also use averaging. Link to comment Share on other sites More sharing options...
Pierre Posted May 23, 2020 Author Share Posted May 23, 2020 That sounds very nice, thank you ! In fact, I just heard about Analog Discovery 2... two days ago and then did not buy anything yet. But the (fast) increasing capabilities seem more and more interesting to me. Questions still worry me : - Is 20mVp signal amplitude still OK from point of view of noise ? First, there could be generator noise for such a small amplitude -> that's why I asked fo possibility to use an external one to master this issue separately in case of integrated AWG performance limitations. But more important may be voltage measurement noise issues because both impedance analyzer resistance and load mesured voltages will be lower than this value. So I wonder if op-amp instrumentation amplifiers would be needed or not ? If yes, would it be possible to interface them between impedance analyzer and scope inputs ? - I did not find anything precise concerning calibration processes in Analog Discovery 2 or WaveForms 2015 Reference Manual. Did I miss something ? Sorry for all those (tough) questions... Pierre. Link to comment Share on other sites More sharing options...
attila Posted May 22, 2020 Share Posted May 22, 2020 Hi @Pierre The last WF beta version adds option and example to perform Offset sweep:https://forum.digilentinc.com/topic/8908-waveforms-beta-download/ Select Custom Mode, click 'Custom Amplitude', under Example select 'Offset sweep' and adjust the low/high offset values, amplitude. Specify identical Start/Stop frequencies. The % X axis will represent low and high offset values. Specially for low capacitance values (pF) the open compensation is recommended, click 'Compensation' under Options. In case you are using external Wavegen signal amplification (#X or attenuation 0.#X) or Scope input attenuation (#X or amplification 0.#X) you can specify these under Options. Link to comment Share on other sites More sharing options...
attila Posted May 22, 2020 Share Posted May 22, 2020 Hi @Pierre Currently offset sweep is not supported, but I will shortly come back with a version supporting it. Link to comment Share on other sites More sharing options...
Question
Pierre
Hello,
I just discovered Analog Discovery 2...today and I'm very interested in impedance measurements capabilities.
I would like to perform capacitance measurements of semiconductors to characterize them.
Therefore I need to operate under AC small amplitude level (about 20mV) and under sweeping DC voltage (range of a few volts, say -4V to +1V).
So I have at least 3 questions :
- Is that kind of measurement record possible with this device ? Specific program needed ?
- Should I use the internal generator with some signal attenuation or use an external (fixed frequency) generator ?
- Other potential problems to take care of (concerning calibration for instance) ?
Many thanks.
Pierre.
P.S : I would like to perform I/V measurements as well but that should not be a problem I guess...
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