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university:tools:m2k:scopy:adcdigitalfilters [11 May 2020 17:10] – [ADC digital filters] Pop Andreeauniversity:tools:m2k:scopy:adcdigitalfilters [01 Jul 2022 16:03] (current) – add clarification note on exponential compensation Doug Mercer
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 These types of filters can be used to process digital signals just as you would use RC networks to frequency compensate analog signals. This includes: DC removal, high-frequency noise These types of filters can be used to process digital signals just as you would use RC networks to frequency compensate analog signals. This includes: DC removal, high-frequency noise
 suppression, wave shaping, smoothing, etc. suppression, wave shaping, smoothing, etc.
 +
 +<note tip>
 +**Exponential compensation**\\
 +The software frequency compensation technique used in Scopy is often called Exponential compensation which adds one or more exponentially decaying terms to a step in the signal. With 2 available stages, Scopy can correct for multiple spurious inductances and capacitances in the internal or external input divider circuit (such as a 10X probe). **Exponential compensation works best for overshoots and undershoots smaller than about 10% of the step height.** In this case, a sum of exponential terms is an accurate generic model for such defects.
 +</note>
  
 The digital filters provide a solution for the hardware calibration mismatch issue between low gain and high gain modes. The setting of these compensation parameters can be determined by following these steps. The Signal Generator outputs of the ADALM2000 should be connected to the Oscilloscope inputs. Oscilloscope +1 to Signal Generator CH 1 and Oscilloscope 2+ to Signal Generator CH 2 with 1- and 2- tied to GND. The Signal Generator channels should be set for Square wave shape and the amplitude set to +2.4 V with 0 offset. Set the Frequency to 4 KHz ( generally a good place to start but other frequencies might work better ). Adjust the Scope time scale to show two cycles of the waveform. With the vertical scale set to 0.5 V/Div observe the shape of the waveform. If the hardware trim was done properly the top and bottom of the wave should be flat. Now switch to 1.0 V/Div setting. The waveform might now be either under or over compensated. If it is under compensated the gain correction parameter should be a positive number. If it is over compensated the gain correction parameter should be a negative number. The value of the gain parameter can be estimated by the ratio of the size of the exponential portion of the waveform to the settled wave amplitude ( P-P step ) which is 4.8 V in this case. The Time Constant parameter can be estimated from the 63% settled time point in the waveform in microSeconds. Once these estimated values are entered and the filter is enabled further fine tuning of the values can be done to make the wave as square topped as possible. The digital filters provide a solution for the hardware calibration mismatch issue between low gain and high gain modes. The setting of these compensation parameters can be determined by following these steps. The Signal Generator outputs of the ADALM2000 should be connected to the Oscilloscope inputs. Oscilloscope +1 to Signal Generator CH 1 and Oscilloscope 2+ to Signal Generator CH 2 with 1- and 2- tied to GND. The Signal Generator channels should be set for Square wave shape and the amplitude set to +2.4 V with 0 offset. Set the Frequency to 4 KHz ( generally a good place to start but other frequencies might work better ). Adjust the Scope time scale to show two cycles of the waveform. With the vertical scale set to 0.5 V/Div observe the shape of the waveform. If the hardware trim was done properly the top and bottom of the wave should be flat. Now switch to 1.0 V/Div setting. The waveform might now be either under or over compensated. If it is under compensated the gain correction parameter should be a positive number. If it is over compensated the gain correction parameter should be a negative number. The value of the gain parameter can be estimated by the ratio of the size of the exponential portion of the waveform to the settled wave amplitude ( P-P step ) which is 4.8 V in this case. The Time Constant parameter can be estimated from the 63% settled time point in the waveform in microSeconds. Once these estimated values are entered and the filter is enabled further fine tuning of the values can be done to make the wave as square topped as possible.
university/tools/m2k/scopy/adcdigitalfilters.txt · Last modified: 01 Jul 2022 16:03 by Doug Mercer