Microchip Technology ARD00342 Data Sheet
© 2011 Microchip Technology Inc.
DS22192D-page 21
MCP3901
4.8
Integral Nonlinearity Error
Integral nonlinearity 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.
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.
offset and gain errors for a DC input signal.
4.9
Signal-to-Noise Ratio (SNR)
For the MCP3901 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
calculation mainly depends on the OSR and DITHER
settings of the device.
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
calculation mainly depends 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)
Distortion (SINAD)
The most important figure of merit, for the analog
performance of the ADCs present on the MCP3901, is
the Signal-to-Noise and Distortion (SINAD)
specification.
performance of the ADCs present on the MCP3901, is
the Signal-to-Noise and Distortion (SINAD)
specification.
Signal-to-Noise and distortion ratio are similar to the
Signal-to-Noise ratio, with the exception that you must
include the harmonics power in the noise power
calculation. The SINAD specification mainly depends
on the OSR and DITHER settings.
Signal-to-Noise ratio, with the exception that you must
include the harmonics power in the noise power
calculation. The SINAD specification mainly depends
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:
following formula also yields SINAD:
EQUATION 4-6:
SINAD, THD AND SNR
RELATIONSHIP
RELATIONSHIP
4.11
Total Harmonic Distortion (THD)
The total harmonic distortion is the ratio of the output
harmonic’s power to the fundamental signal power for
a sinewave input and is defined by
harmonic’s power to the fundamental signal power for
a sinewave input and is defined by
:
EQUATION 4-7:
The THD calculation includes the first 35 harmonics for
the MCP3901 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:
the MCP3901 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.
setting.
4.12
Spurious-Free Dynamic Range
(SFDR)
(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.
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
=