AD7274 datasheet(15/28 Pages) AD

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AD7273/AD7274

Rev. 0 | Page 14 of 28

TERMINOLOGY

Integral Nonlinearity (INL)

The maximum deviation from a straight line passing through

the endpoints of the ADC transfer function. For the AD7273/

AD7274, the endpoints of the transfer function are zero scale at

0.5 LSB below the first code transition and full scale at 0.5 LSB

above the last code transition.

Differential Nonlinearity (DNL)

The difference between the measured and the ideal 1 LSB

change between any two adjacent codes in the ADC.

Offset Error

The deviation of the first code transition (00 . . . 000) to (00 . . .

001) from the ideal, that is, AGND + 0.5 LSB.

Gain Error

The deviation of the last code transition (111 . . . 110) to

(111 . . . 111) from the ideal, that is, VREF – 1.5 LSB, after

adjusting for the offset error.

Total Unadjusted Error (TUE)

A comprehensive specification that includes gain, linearity, and

offset errors.

Track-and-Hold Acquisition Time

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

to reach its final value, within ±0.5 LSB, after the end of the

conversion. See the Serial Interface section for more details.

Signal-to-Noise + Distortion Ratio (SINAD)

The measured ratio of signal to noise plus distortion at the

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

fundamental, and noise is the rms sum of all nonfundamental

signals up to half the sampling frequency (fS/2), including

harmonics but excluding dc. The ratio is dependent on the

number of quantization levels in the digitization process: the

more levels, the smaller the quantization noise. For an ideal N-bit

converter, the SINAD is

SINAD

According to this equation, the SINAD is 74 dB for a 12-bit

converter and 62 dB for a 10-bit converter. However, various

error sources in the ADC, including integral and differential

nonlinearities and internal ac noise sources, cause the measured

SINAD to be less than its theoretical value.

Total Harmonic Distortion (THD)

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

defined as:

()

log

THD

where V1 is the rms amplitude of the fundamental, and V2, V3,

, V5, and V6 are the rms amplitudes of the second through the

sixth harmonics.

Peak Harmonic or Spurious Noise (SFDR)

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

ADC output spectrum (up to f /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; however,

for ADCs with harmonics buried in the noise floor, it is deter-

mined by a noise peak.

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 and

n = 0, 1, 2, 3, …. Intermodulation distortion terms are those for

which neither m nor n are equal to zero. 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 AD7273/AD7274 are tested using the CCIF standard in

which two input frequencies are used (see fa and fb in the

Specifications section). 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 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 fundamentals expressed in decibels.

Power Supply Rejection Ratio (PSRR)

The ratio of the power in the ADC output at full-scale

frequency, f, to the power of a 100 mV p-p sine wave applied to

the ADC V

supply of frequency f .

( )

(

)

PSRR

log

dB =

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

the power at frequency fS coupled onto the ADC VDD supply.

Aperture Delay

The measured interval between the leading edge of the sampling

clock and the point at which the ADC actually takes the sample.

Aperture Jitter

The sample-to-sample variation in the effective point in time at

which the sample is taken.

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