AD7762SLASH datasheet(14/23 Pages) AD

14 / 23 page

Data Sheet

AD7767

TERMINOLOGY

analog.com

Rev. D | 14 of 23

Signal-to-Noise Ratio (SNR)

SNR is the ratio of the actual input signal’s rms value 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.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of harmonics to the fundamental.

For the AD7767, it is defined as

( )

THD

log

(1)

where:

V1 is the rms amplitude of the fundamental.

V2, V3, V4, V5, and V6 are the rms amplitudes of the second to the

sixth harmonics.

Nonharmonic Spurious-Free Dynamic Range

(SFDR)

SFDR is the ratio of the rms signal amplitude to the rms value of the

peak spurious spectral component, excluding harmonics.

Dynamic Range

Dynamic range is the ratio of the rms value of the full scale to the

rms noise measured with the inputs shorted together. The value for

the dynamic range is expressed in decibels.

Intermodulation Distortion (IMD)

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

any active device with nonlinearities creates distortion products at

sum and difference frequencies of mfa ± nfb, where m, n = 0, 1, 2,

3, and so on. Intermodulation distortion terms are those for which

neither m nor 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 AD7767 is tested using the CCIF standard, where two input

frequencies near the top end of the input bandwidth are used.

In this case, the second-order terms are usually distanced in fre-

quency from the original sine waves, and the third-order terms

are usually at a frequency close to the input frequencies. As a

result, the second- 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 funda-

mentals expressed in decibels.

Integral Nonlinearity (INL)

INL is the maximum deviation from a straight line passing through

the endpoints of the ADC transfer function.

Differential Nonlinearity (DNL)

DNL is the difference between the measured and the ideal 1 LSB

change between any two adjacent codes in the ADC.

Zero Error

Zero error is the difference between the ideal midscale input voltage

(when both inputs are shorted together) and the actual voltage

producing the midscale output code.

Zero Error Drift

Zero error drift is the change in the actual zero error value due to a

temperature change of 1°C. It is expressed as a percentage of full

scale at room temperature.

Gain Error

The first transition (from 100 … 000 to 100 … 001) should occur

½ LSB above the nominal negative full scale for an analog voltage.

The last transition (from 011 … 110 to 011 … 111) should occur 1½

LSB below the nominal full scale for an analog voltage. 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 change in the actual gain error value due to a

temperature change of 1°C. It is expressed as a percentage of full

scale at room temperature.

Common-Mode Rejection Ratio (CMRR)

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

full-scale frequency f to the power of a 100 mV sine wave applied to

the common-mode voltage of the VIN+ and VIN− inputs at frequency

fS.

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

(2)

where Pf is the power at the frequency f in the ADC output, and PfS

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

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