AD7656ABSTZ datasheet(13/28 Pages) ETC2

13 / 28 page

Data Sheet

AD7656A

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, a 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-Scale Error

The bipolar zero-scale error is the deviation of the midscale

transition (all 1s to all 0s) from the ideal VIN voltage, that is,

AGND − 1 LSB.

Bipolar Zero-Scale Error Matching

The bipolar zero-scale error matching is the difference in

bipolar zero-code error between any two input channels.

Positive Full-Scale Error

The positive full-scale error is the deviation of the last code

transition (011 … 110) to (011 … 111) from the ideal (4 × VREF –

1 LSB or 2 × VREF − 1 LSB) after adjusting for the bipolar zero

scale error.

Positive Full-Scale Error Matching

The positive full-scale error matching is the difference in

positive full-scale error between any two input channels.

Negative Full-Scale Error

The negative full-scale error is the deviation of the first code

transition (10 … 000) to (10 … 001) from the ideal (−4 × VREF +

1 LSB or −2 × VREF + 1 LSB) after adjusting for the bipolar zero-

code error.

Negative Full-Scale Error Matching

The negative full-scale error matching is 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 Ratio (SNR)

SNR is the ratio of the rms value of the measured output signal

to the rms sum of all other spectral components below the

Nyquist frequency. The value for SNR is expressed in decibels.

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

The SINAD ratio is the measured ratio of signal-to-noise-and-

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

(fSAMPLE/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 SINAD ratio for an ideal N-bit converter

with a sine wave input is given by

SINAD = (6.02 N + 1.76) dB

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

Total Harmonic Distortion (THD)

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

fundamental. For the AD7656A, it is defined as

log

)

(

THD

where:

V1 is the rms amplitude of the fundamental.

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

through sixth harmonics.

Peak Harmonic or Spurious Noise

The peak harmonic or spurious noise is the ratio of the rms value

of the next largest component in the ADC output spectrum (up

to fSAMPLE/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 (IMD)

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

fb, any active device with nonlinearities create 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 are 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 AD7656A is tested using the CCIF standard in which two

input frequencies near the maximum input bandwidth are used.

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

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.

Rev. 0 | Page 13 of 28

AD7656ABSTZ 数据表(PDF) 13 Page - List of Unclassifed Manufacturers

AD7656ABSTZ 数据表(HTML) 13 Page - List of Unclassifed Manufacturers

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

数据表下载