Hi, We have a digitizer, and we want to calculate it's response (pole- zero or amplitude-phase of the system),
knowing the chip used in digitizer, we know that it has 24-Bit resolution, and it's peak-peak is 5 (+-2.5) volts, Now, if anyone can suggest a way to obtain the response? For example by giving the step input (with a signal generator and obtain the outputs in counts),
Furthermore, How sampling rate affect the response, should we calculate one specific response for each sampling rate?
Thank you,
Hello Hossein,
Yes, you can get a feel of the converters/digitizers (ADC) behavior.
I believe you have 24-bit ADC so it must be sampling at a slower rates or few SPS (samples per second) to a couple of kilo SPS. (kSPS)!
What you can do is collect some large number of samples, >4k, typically in the binary order such as 4096, 8192 ....etc for a known sine wave input of certain level (dB or dBm).
Run FFT on these data sets and it will reveal a lot including SNR etc. and probably you can also find the ENOB -effective number of bits.
You can then play around with different frequencies and sampling rates and also study the behavior of the converter against a STEP input.
I hope this helps you to solve your problem.
Best wishes!
-Prasanna Waichal
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Thank you for your help, I am really appreciated, Here you can see the step response of the ADC, the 1-Hz step input had 100 millisecond duration and amplitude of 50 millivolt. the digitizer outputs were recorded for three sampling rate of 200, 100. and 50 SPS. Now, what I'm looking for is some algorithm to extract the response of the ADC.
Dear Hossein,
welcome!
It is me strange how the output of an A/D converter has the form displayed by you in the picture. The analog to digital converters input is an analog wave form. This wave form is sampled by a sample and hold circuit. Then the sampled value is converted to a binary digital form of bits. Every sample is encoded to an n-bit code. The resolution of the A/D converter depends on its code length n.
The sampling time which is the denoted by Ts which is the time between two consequent samples is divided into two parts, the sample acquisition time, which is the time required to take a sample and the conversion time where the the acquired sample is stored in a capacitor and then input to a qauntizer circuit to convert it to an n bit form.
So, dynamically the A.D converter is characterized by a specific conversion speed or highest sampling frequency. This frequency is dictated by the minimum acquisition time plus the minimum encoding time.
I could not understand your question as the dynamics of the A/D converter is defined by the highest sampling frequency. What do you want to achieve by your time step response. This circuit is a mixed analog and digital circuit.
Best wishes
Hello,
I think what you can do is try to save the numerical data values of the signals captured as shown above on your PC through your Data Acquisition software. Then save the data array as table or file and calculate the FFT using any data analysis tools or MATLAB, Python, etc. This FFT plot should reveal important information that you are looking for for the impulse input sampled at different sampling rates.
Hope you will get satisfactory results.
Do share your test results.
Best luck!
Hello, like the colleages I recommend to use some numerical tool to see the fft of the signal. On the other hand, I suggest you to see this book:
Prentice Hall - Software Radio A Modern Approach to Radio Engineering Jeffrey Reed and maybe this other link mey be helpfull
http://www.analog.com/media/en/training-seminars/tutorials/MT-085.pdf
Regards
Hello Hossein,
Could you find the FFT of the pulse response?
Can you share the data values of this responses at each of the sampling speed?
Thanks and best wishes!
Hello Prasanna,
Thank you for your response,
I have decided to use MATLAB's System Identification Toolbox, and I have used an generated SINC Function (using a signal generator- type AFG-2225) as an input signal, then the output signal acquired from the digitizer (recorded on hard drive),
then I have imported this data set in to the MATALB, and estimate the response of the system with 2 poles and 1 zero,
you can find the results for 200 sample per second in the attached figures ,
please let me know if I did it Right,
Hello Hossein,
Yes, you are on the right track. And I further understand that you have sampled the input signal at 200SPS.
Well, can I invite your kind attention to your own answer a year ago where you have shown your various input signals via 1.png graphics file.
I can see that you had fed a 50mV signal with 1Hz, 10% duty cycle and have sampled this pulse signal with various rates as 50, 100 and 200 SPS rates.
Now you have acquired the technique as to how to sample the signal, get the data and analyze using some tools like MATLAB, you repeat the same 1Hz 10% square wave input and check how your ADC is responding in a similar way as the you have fed this SINC input.
And see what results you get? Hopefully you shall get what you have been looking for such a long period of time!
Bye the way kindly accept my belated Ramadan Greetings!
All the best!
-Prasanna
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