MCP3464 datasheet(28/108 Pages) MICROCHIP

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MCP3461/2/4

DS20006180D-page 28

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4.5

OSR – Oversampling Ratio

The ratio of the sampling frequency to the output data

rate. OSR = DMCLK/(DRCLK) in Continuous mode.

See Table 5-6 for the OSR setting effect on sinc filter

parameters.

4.6

Offset Error

This is the error induced by the ADC when the inputs

are shorted together (VIN = 0V). This error varies based

on gain settings, OSR settings and from chip to chip. It

can easily be calibrated out by a MCU with a

subtraction.

4.7

Gain Error

This is the error induced by the ADC on the slope of the

transfer function. It is the deviation expressed in

percentage compared to the ideal transfer function

defined by Equation 5-5. The specification incorporates

ADC gain error contributions, but not the VREF

contribution. This error varies with GAIN and OSR

settings.

The gain error of this device has a low-temperature

coefficient.

4.8

Integral Nonlinearity Error (INL)

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 static error after calibration

of offset and gain errors for a DC input signal.

4.9

Signal-to-Noise Ratio (SNR)

For this device family, 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 sine wave 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 GAIN settings of the

device as well as temperature (due to thermal noise

being dominant for high OSR).

EQUATION 4-4:

SIGNAL-TO-NOISE RATIO

4.10

Signal-to-Noise and Distortion

Ratio (SINAD)

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 GAIN settings.

EQUATION 4-5:

SINAD EQUATION

The calculated combination of SNR and THD per

Equation 4-6 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 sine wave input and is defined by Equation 4-7.

EQUATION 4-7:

The THD is usually only measured with respect to the

ten first harmonics. THD is sometimes expressed in

percentage (%). For converting the THD from “dB” to

“%”, apply the formula in Equation 4-8.

EQUATION 4-8:

4.12

Spurious-Free Dynamic Range

(SFDR)

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 OSR and GAIN 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 10

THD dB



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



SFDR dB



FundamentalPower

HighestSpurPower

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





log

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