MCP3901 datasheet(21/62 Pages) MICROCHIP

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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.

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 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.

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 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.

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

harmonic’s power to the fundamental signal power for

a sinewave input and is defined by Equation 4-7:

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:

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

()

SignalPower

NoisePower

----------------------------------

⎝⎠

⎛⎞

log

SINAD dB

()

SignalPower

Noise

HarmonicsPower

---------------------------------------------------------------------

⎝⎠

⎛⎞

log

SINAD dB

()

SNR

-----------

⎝⎠

⎛⎞

THD

–

----------------

⎝⎠

⎛⎞

log

THD dB

()

HarmonicsPower

FundamentalPower

-----------------------------------------------------

⎝⎠

⎛⎞

log

THD %

()

100

THD dB

()

------------------------

SFDR dB

()

FundamentalPower

HighestSpurPower

-----------------------------------------------------

⎝⎠

⎛⎞

log

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