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Data Sheet

AD7764

Rev. B | Page 15 of 33

TERMINOLOGY

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 (dB).

Total Harmonic Distortion (THD)

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

fundamental. For the AD7764, THD is defined as

THD(dB) = 20log

where:

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

to the sixth harmonics.

V1 is the rms amplitude of the fundamental.

Nonharmonic Spurious-Free Dynamic Range (SFDR)

Nonharmonic 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 dynamic range is expressed in decibels.

Intermodulation Distortion

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 is equal to 0. For example, the second-

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

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

The AD7764 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 typically distanced in

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

are typically 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 per the THD

specification, where the calculation 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.

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 code transition (from 100 … 000 to 100 … 001) occurs

for an analog voltage 1/2 LSB above the nominal negative full

scale. The last code transition (from 011 … 110 to 011 … 111)

occurs for an analog voltage 1 ½ LSB below the nominal full scale.

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.

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