Datasheet

© 2011 Microchip Technology Inc. DS25048B-page 19
MCP3903
4.8 Integral Non-Linearity Error
Integral non-linearity error is the maximum deviation of
an ADC transition point from the corresponding point of
an ideal transfer function, with the offset and gain
errors removed, or with the end points equal to zero.
It is the maximum remaining error after calibration of
offset and gain errors for a DC input signal.
4.9 Signal-To-Noise Ratio (SNR)
For the MCP3903 ADC, the signal-to-noise ratio is a
ratio of the output fundamental signal power to the
noise power (not including the harmonics of the signal),
when the input is a sinewave at a predetermined
frequency. It is measured in dB. Usually, only the
maximum signal to noise ratio is specified. The SNR
figure depends mainly on the OSR and DITHER
settings of the device.
EQUATION 4-4: SIGNAL-TO-NOISE RATIO
4.10 Signal-To-Noise Ratio And
Distortion (SINAD)
The most important figure of merit for the analog
performance of the ADCs present on the MCP3903 is
the Signal-to-Noise And Distortion (SINAD)
specification.
Signal-to-noise and distortion ratio is similar to signal-
to-noise ratio, with the exception that you must include
the harmonics power in the noise power calculation.
The SINAD specification depends mainly on the OSR
and DITHER settings.
EQUATION 4-5: SINAD EQUATION
The calculated combination of SNR and THD per the
following formula also yields SINAD:
EQUATION 4-6: SINAD, THD, AND SNR
RELATIONSHIP
4.11 Total Harmonic Distortion (THD)
The total harmonic distortion is the ratio of the output
harmonics power to the fundamental signal power for a
sinewave input and is defined by the following
equation.
EQUATION 4-7:
The THD calculation includes the first 35 harmonics for
the MCP3903 specifications. The THD is usually only
measured with respect to the 10 first harmonics. THD
is sometimes expressed in %. For converting the THD
in %, here is the formula:
EQUATION 4-8:
This specification depends mainly on the DITHER
setting.
4.12 Spurious-Free Dynamic Range
(SFDR)
SFDR is the ratio between the output power of the
fundamental and the highest spur in the frequency
spectrum. The spur frequency is not necessarily a
harmonic of the fundamental even though it is usually
the case. This figure represents the dynamic range of
the ADC when a full-scale signal is used at the input.
This specification depends mainly on the DITHER
setting.
EQUATION 4-9:
SNR dB() 10
SignalPower
NoisePower
----------------------------------
⎝⎠
⎛⎞
log=
SINAD dB() 10
SignalPower
Noise HarmonicsPower+
--------------------------------------------------------------------
⎝⎠
⎛⎞
log=
SINAD dB() 10 10
SNR
10
-----------
⎝⎠
⎛⎞
10
THD–
10
----------------
⎝⎠
⎛⎞
+log=
THD dB() 10
HarmonicsPower
FundamentalPower
-----------------------------------------------------
⎝⎠
⎛⎞
log=
THD %() 100 10
THD dB()
20
------------------------
×=
SFDR dB() 10
FundamentalPower
HighestSpurPower
-----------------------------------------------------
⎝⎠
⎛⎞
log=