AD7768 datasheet(40/106 Pages) AD

40 / 106 page

Data Sheet

AD7768/AD7768-4

TERMINOLOGY

analog.com

Rev. C | 40 of 106

AC Common-Mode Rejection Ratio (AC CMRR)

AC CMRR is defined as the ratio of the power in the ADC output

at frequency, f, to the power of a sine wave applied to the common-

mode voltage of AINx+ and AINx− at sampling frequency, fS.

AC CMRR (dB) = 10log(Pf/PfS)

where:

Pf is the power at frequency, f, in the ADC output.

PfS is the power at frequency, fS, in the ADC output.

Gain Error

The first transition (from 100 … 000 to 100 … 001) occurs at

a level ½ LSB above nominal negative full scale (−4.0959375 V

for the ±4.096 V range). The last transition (from 011 … 110 to

011 … 111) occurs for an analog voltage 1½ LSB below the nominal

full scale (4.0959375 V for the ±4.096 V range). The gain error

is the deviation of the difference between the actual level of the

last transition and the actual level of the first transition from the

difference between the ideal levels.

Gain Error Drift

Gain error drift is the gain error change due to a temperature

change of 1°C. It is expressed in parts per million per degree

Celsius.

Integral Nonlinearity (INL) Error

INL error refers to the deviation of each individual code from a

line drawn from negative full scale through positive full scale. The

point used as negative full scale occurs ½ LSB before the first code

transition. Positive full scale is defined as a level 1½ LSB greater

than the last code transition. The deviation is measured from the

middle of each code to the true straight line.

Intermodulation Distortion (IMD)

With inputs consisting of sine waves at two frequencies, fa and fb,

any active device with nonlinearities creates distortion products at

the sum and difference frequencies of mfa and nfb, where m, n =

0, 1, 2, 3, and so on. Intermodulation distortion terms are those for

which neither m or n are equal to 0. For example, the second-order

terms include (fa + fb) and (fa − fb), and the third-order terms

include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb).

The AD7768/AD7768-4 are tested using the CCIF standard, where

two input frequencies near to each other are used. In this case,

the second-order terms are usually distanced in frequency from the

original sine waves, and the third-order terms are usually at a fre-

quency close to the input frequencies. As a result, the second-order

and third-order terms are specified separately. The calculation of

the intermodulation distortion is as per the THD specification, where

it is the ratio of the rms sum of the individual distortion products

to the rms amplitude of the sum of the fundamentals, expressed in

decibels.

Least Significant Bit (LSB)

The least significant bit, or LSB, is the smallest increment that can

be represented by a converter. For a fully differential input ADC with

N bits of resolution, the LSB expressed in volts is as follows:

LSB (V) = (2 × VREF)/2N

For the AD7768/AD7768-4, VREF is the difference voltage between

the REFx+ and REFx− pins, and N = 24.

Offset Error

Offset error is the difference between the ideal midscale input

voltage (0 V) and the actual voltage producing the midscale output

code.

Power Supply Rejection Ratio (PSRR)

Variations in power supply affect the full-scale transition but not

the linearity of the converter. PSRR is the maximum change in

the full-scale transition point due to a change in the power supply

voltage from the nominal value.

Signal-to-Noise Ratio (SNR)

SNR is the ratio of the rms value of the actual input signal to

the rms sum of all other spectral components below the Nyquist

frequency, excluding harmonics and dc. The value for SNR is

expressed in decibels.

Signal-to-Noise-and-Distortion Ratio (SINAD)

SINAD is the ratio of the rms value of the actual input signal to

the rms sum of all other spectral components below the Nyquist

frequency, including harmonics but excluding dc. The value for

SINAD is expressed in decibels.

Spurious-Free Dynamic Range (SFDR)

SFDR is the difference, in decibels, between the rms amplitude of

the input signal and the peak spurious signal (excluding the first five

harmonics).

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of the first five harmonic compo-

nents to the rms value of a full-scale input signal and is expressed

in decibels.

AD7768 Datasheet(PDF) 40 Page - Analog Devices

AD7768 Datasheet(HTML) 40 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL