MCP3564-ESLASHST datasheet(28/108 Pages) MICROCHIP

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MCP3561/2/4

DS20006181C-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 an 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 per-

centage 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 offset and

gain errors calibration 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 the 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 the

following formula also yields SINAD:

EQUATION 4-6:

SINAD, THD AND SNR

RELATIONSHIP

4.11

Total Harmonic Distortion (THD)

The THD is the ratio of the output harmonics power to

the fundamental signal power for a sine wave input and

is defined by the following equation.

EQUATION 4-7:

The THD is usually measured only with respect to the

first ten harmonics. THD is sometimes expressed in

percentage (%). This formula converts the THD from

dB to percentage:

EQUATION 4-8:

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 har-

monic of the fundamental, even though that 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

settings.

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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