This tool is intended to show the capabilities of the ADCs of the modules TEI0015, TEI0016A, TEI0016B, TEI0023A, and TEI0023B via FFT and DNL analysis. FFT and DNL signal analysis complement each other.
To show the quality of the input signal the well known FFT (Fast Fourier Transformation) can be used. The overall precision of the ADC can be evaluated by DNL and INL (Differential / Integral non linearity) analysis.
FFT - 101.09 Hz sine wave - 1024 kSamples
DNL - 101.09 Hz sine wave - 64 MSamples
The section Module contains radio buttons for setting up the parameters:
Gain - Select the signal / wave pre-amplification.
Samples FFT - Select the sample length of consecutive data points for the FFT analysis.
Samples DNL - Select the non consecutive size of data points for a DNL analysis.
Input Span Compression - Feature of modules TEI0015 and TEI0023, which reduces ADC reference voltage to 0.8.
High-Z Mode - Feature of modules TEI0015 and TEI0023, which reduces ADC current consumption.
The section Generator controls the square wave generator.
The section Help contains links to the product page of every module and information about the program.
Connect - Connects via UART / Serial connection to the module.
Disconnect - Terminates the connection to a module.
The following buttons are only enabled when a connection is established and after an analysis has been performed. During an analysis these buttons are disabled.
Wave / FFT - Triggers a FFT analysis according to the parameters set in the section Module.
Save wave to C:\temp\capture.txt - Available after a FFT analysis, saves the measured ADC values of the previous FFT analysis. The values are stored as integers in a text-file at c:\temp\capture.txt . The folder needs to created manually.
Start / Stop DNL - Begins a DNL / INL analysis according to the parameters set in the section Module. When pressed during an analysis it terminates the analysis.
Save DNL histogramm to c:\temp\histogram.txt - Saves the histogram values of a previous DNL analysis. The values are stored as integers in a text-file at c:\temp\histogram.txt . The folder needs to created manually.
Switch graphs FFT / DNL - Switches between the different sets of graphs for FFT and DNL analysis.
Input Signal for a DNL analysis
The DNL analysis assumes a sine wave input. The validity of its results depends heavily on the quality of the sine wave input signal. The better the sine wave input signal the more meaningful the results will become.
The sine wave should have an amplitude just above 100 %, therefore some clipping occurs and all ADC codes are present in the analysis. The sample length should ensure the average data points per ADC code to be well above 150.
These values are visible in the lower part of the statistic section to the right under DNL / INL statistics: .
An other aid for good results is the input frequency. The construction of the modules leads to a desired input frequency of 101.09 Hz. Best practice is to supply the input signal differentially.
Apply a signal to the modules inputs. Connect a single module to your PC and start the program. Press Connect for a connection to the module. A connection applies the default Gain of 1, enables the buttons Wave/FFT, DNL/INL and the sections Module and Generator.
Select values for pre-amplification
Gain, Sample FFT respectively Samples DNL and module specific features as you like. Press Wave / FFT or DNL / INL to run the analysis.
During operation, the sections Module, Generator and most buttons will be disabled and afterwards re-enabled. Additional buttons / functions are available after an analysis.
After a FFT analysis, the graphs are plotted, the signal statistics will be evaluated and the button Save wave to C:\temp\capture.txt is enabled. The button stores the Integer wave values from the ADC as text-file for interaction with the demo Data Capture.
A DNL consists of two steps, first a FFT analysis, second the DNL analysis. Following the DNL analysis, the buttons Save DNL histogramm to c:\temp\histogram.txt and Show DNL / INL (Show Wave / FFT) will be enabled. The statistics for DNL are updated.
Disconnecting from the module or closing the program disables all module specific features and the square wave generator.