MCP3903 ADC Evaluation Board for 16-Bit MCUs User’s Guide
DS51994A-page 14
©
2011 Microchip Technology Inc.
The Waveform Graphs will show the signal in Time domain, while the Signal Spectrum
graphs shows the signal in Frequency domain. From the
Graphs
menu, under the
Signal Spectrum
option, the user can find the
Switch Y-axis scale
option. From here,
it is possible to change the Y axis of the Signal Spectrum in linear scale or in logarithmic
scale. The spectrum signal information is obtained by performing a Fast Fourier
transformation over the Time domain signal. This Fourier transformation can be done
after the signal has been windowed. For this, the user must select the type of window
from the
Window
control on the lower area of the main window.
The Histogram Graph can be used to investigate the distribution of the codes. This is
especially helpful to check if a DC signal distribution is Gaussian. From the
Graphs
menu, under the
Histogram
option, the user can
Change the number of bits
, with the
default being 40.
The indicators from the lower area of the program indicate other performance
parameters of the ADC. The main one is SINAD and related to it is Effective Number
of Bits (ENOB), used to indicate the AC signal performance. The ENOB value is
computed according to the formula below:
EQUATION 2-1:
For DC signals, the Noise RMS signal in µV is displayed. For AC signals, the indicator
will show the RMS value of the signal.
ENOB
SINAD
1.76
–
6.02
------------------------------------
=
