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Data Sheet

AD7609

Rev. A | Page 19 of 36

TERMINOLOGY

Integral Nonlinearity

The maximum deviation from a straight line passing through

the endpoints of the ADC transfer function. The endpoints of

the transfer function are zero scale, a ½ LSB below the first code

transition, and full scale at ½ LSB above the last code transition.

Differential Nonlinearity

The difference between the measured and the ideal 1 LSB

change between any two adjacent codes in the ADC.

Bipolar Zero Code Error

The deviation of the midscale transition (all 1s to all 0s) from

the ideal VIN voltage, that is, AGND.

Bipolar Zero Code Error Match

The difference in bipolar zero code error between any two input

channels.

Positive Full-Scale Error

The last transition (from 011 . . . 10 to 011 . . . 11 in twos

complement coding) should occur for an analog voltage 1½

LSB below the nominal full scale (9.99977 V for the ±10 V

range and 4.99988 V for the ±5 V range). The positive full-scale

error is the deviation of the actual level of the last transition

from the ideal level.

Positive Full-Scale Error Match

The difference in positive full-scale error between any two input

channels.

Negative Full-Scale Error

The first transition (from 100 . . . 00 to 100 . . . 01 in twos

complement coding) should occur for an analog voltage ½ LSB

above the negative full scale (−9.999923 V for the ±10 V range

and −4.9999618 for the ±5 V range). The negative full-scale

error is the deviation of the actual level of the first transition

from the ideal level.

Negative Full-Scale Error Match

The difference in negative full-scale error between any two

input channels.

Track-and-Hold Acquisition Time

The track-and-hold amplifier returns to track mode at the end

of the conversion. The track-and-hold acquisition time is the

time required for the output of the track-and-hold amplifier to

reach its final value, within ±1 LSB, after the end of the conversion.

See the Track-and-Hold Amplifiers section for more details.

Signal-to-(Noise + Distortion) Ratio

The measured ratio of signal-to-(noise + distortion) at the

output of the ADC. The signal is the rms amplitude of the

fundamental. Noise is the sum of all nonfundamental signals

up to half the sampling frequency (fS/2, excluding dc). The ratio

depends on the number of quantization levels in the digitization

process: the more levels, the smaller the quantization noise. The

theoretical signal-to-(noise + distortion) ratio for an ideal N-bit

converter with a sine wave input is given by

Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB

Thus, for an 18-bit converter, this is 110.12 dB.

Total Harmonic Distortion (THD)

The ratio of the rms sum of the harmonics to the fundamental.

For the AD7609, it is defined as

THD (dB) =

20log

where:

V1 is the rms amplitude of the fundamental.

V2 to V9 are the rms amplitudes of the second through ninth

harmonics.

Peak Harmonic or Spurious Noise

The ratio of the rms value of the next largest component in the

ADC output spectrum (up to fS/2, excluding dc) to the rms value

of the fundamental. Normally, the value of this specification is

determined by the largest harmonic in the spectrum, but for

ADCs where the harmonics are buried in the noise floor, it is

determined by a noise peak.

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. 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), and the third-order terms

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

The calculation of the intermodulation distortion is 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 (dB).

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