AD7616BSTZ datasheet(22/51 Pages) AD

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Data Sheet

AD7616

Rev. 0 | Page 21 of 50

TERMINOLOGY

Integral Nonlinearity (INL)

INL is 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, at ½ LSB below

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

transition.

Differential Nonlinearity (DNL)

DNL is the difference between the measured and the ideal 1

LSB change between any two adjacent codes in the ADC.

Bipolar Zero Code Error

Bipolar zero code error is the deviation of the midscale

transition (all 1s to all 0s) from the ideal, which is 0 V − ½ LSB.

Bipolar Zero Code Error Matching

Bipolar zero code error matching is the absolute difference in

bipolar zero code error between any two input channels.

Positive Full-Scale (PFS) Error

Positive full-scale error is the deviation of the actual last code

transition from the ideal last code transition (10 V − 1½ LSB

(9.99954), 5 V − 1½ LSB (4.99977) and 2.5 V − 1½ LSB

(2.49989)) after bipolar zero code error is adjusted out. The

positive full-scale error includes the contribution from the

internal reference buffer.

Positive Full-Scale Error Matching

Positive full-scale error matching is the absolute difference in

positive full-scale error between any two input channels.

Negative Full-Scale (NFS) Error

Negative full-scale error is the deviation of the first code

transition from the ideal first code transition (−10 V + ½ LSB

(−9.99985), −5 V + ½ LSB (−4.99992) and −2.5 V + ½ LSB

(−2.49996)) after the bipolar zero code error is adjusted out.

The negative full-scale error includes the contribution from the

internal reference buffer.

Negative Full-Scale Error Matching

Negative full-scale error matching is the absolute difference in

negative full-scale error between any two input channels.

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

SINAD is the measured ratio of signal to noise and distortion at

the output of the ADC. The signal is the rms value of the sine

wave, and noise is the rms sum of all nonfundamental signals

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

but excluding dc.

Signal-to-Noise Ratio (SNR)

SNR is the measured ratio of signal to noise 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 is dependent on the number of quantization levels in

the digitization process: the greater the number of levels, the

smaller the quantization noise. The theoretical SNR for an ideal

N-bit converter with a sine wave input is given by

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

Therefore, for a 16-bit converter, the SNR is 98 dB.

Total Harmonic Distortion (THD)

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

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

expressed in decibels (dB).

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 the 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).

Power Supply Rejection Ratio (PSRR)

Variations in power supply affect the full-scale transition but

not the linearity of the converter. Power supply rejection is the

maximum change in full-scale transition point due to a change

in power supply voltage from the nominal value. The PSRR is

defined as 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 VCC supply of the ADC of frequency, fS.

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

where:

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

PfS is equal to the power at frequency, fS, coupled onto the VCC

supply.

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