AD7851AR datasheet(8/36 Pages) AD

8 / 36 page

AD7851

–8–

REV. B

TERMINOLOGY

Integral Nonlinearity

This is the maximum deviation from a straight line passing

through the endpoints of the ADC transfer function. The end-

points of the transfer function are zero scale, a point 1/2 LSB

below the first code transition, and full scale, a point 1/2 LSB

above the last code transition.

Differential Nonlinearity

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

change between any two adjacent codes in the ADC.

Total Unadjusted Error

This is the deviation of the actual code from the ideal code tak-

ing all errors into account (gain, offset, integral nonlinearity, and

other errors) at any point along the transfer function.

Unipolar Offset Error

This is the deviation of the first code transition (00 . . . 000 to

00 . . . 001) from the ideal AIN(+) voltage (AIN(–) + 1/2 LSB)

when operating in unipolar mode.

Positive Full-Scale Error

This applies to unipolar and bipolar modes and is the deviation of

the last code transition from the ideal AIN(+) voltage (AIN(–) +

full scale – 1.5 LSB) after the offset error has been adjusted out.

Negative Full-Scale Error

This applies to bipolar mode only and is the deviation of the

first code transition (10 . . . 000 to 10 . . . 001) from the ideal

AIN(+) voltage (AIN(–) – VREF/2 + 0.5 LSB).

Bipolar Zero Error

This is the deviation of the midscale transition (all 1s to all 0s)

from the ideal AIN(+) voltage (AIN(–) – 1/2 LSB).

Track-and-Hold Acquisition Time

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

of conversion. Track-and-hold acquisition time is the time

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

its final value, within

±1/2 LSB, after the end of conversion.

Signal-to-(Noise + Distortion) Ratio

This is 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 is

dependent on the number of quantization levels in the digitiza-

tion 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 a 14-bit converter, this is 86 dB.

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the rms sum of

harmonics to the fundamental. For the AD7851, it is defined as

THD

VVV

(d )

20 log

()

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

V4, V5, and V6 are the rms amplitudes of the second through the

sixth harmonics.

Peak Harmonic or Spurious Noise

Peak harmonic or spurious noise is defined as the ratio of the

rms value of the next largest component in the ADC output

spectrum (up to fS/2 and excluding dc) to the rms value of the

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

mined by the largest harmonic in the spectrum, but for parts

where the harmonics are buried in the noise floor, it will be a

noise peak.

Intermodulation Distortion

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

fb, any active device with nonlinearities will create distortion

products at sum and difference frequencies of mfa

± nfb where

m, n = 0, 1, 2, 3, etc. 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), while the

third-order terms include (2fa + fb), (2fa – fb), (fa + 2fb), and

(fa – 2fb).

Testing is performed 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 frequency from the original sine waves while 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 dBs.

Power Supply Rejection Ratio (PSRR)

PSRR is defined as the ratio of the power in ADC output at fre-

quency f to the power of the full-scale sine wave applied to the

supply voltage (VDD). The units are in LSB, % of FS per % of

supply voltage, or expressed logarithmically, in dB (PSRR (dB)

= 10 log (Pf/Pfs)).

Full Power Bandwidth (FPBW)

FPBW is that frequency at which the amplitude of the recon-

structed fundamental (using FFTs and neglecting harmonics

and SNR) is reduced by 3 dB for a full-scale input.

AD7851AR Datasheet(PDF) 8 Page - Analog Devices

AD7851AR Datasheet(HTML) 8 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datasheet Download

Link URL