EVAL-AD7401EB 查看數據表（PDF） - Analog Devices

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EVAL-AD7401EB

Isolated Sigma-Delta Modulator

Analog Devices 

AD7401

TERMINOLOGY

Differential Nonlinearity

Differential nonlinearity is the difference between the measured

and the ideal 1 LSB change between any two adjacent codes

in the ADC.

Integral Nonlinearity

Integral nonlinearity is the maximum deviation from a straight

line passing through the endpoints of the ADC transfer function.

The endpoints of the transfer function are specified negative

full-scale, −200 mV (VIN+ − VIN−), Code 12,288 for the 16-bit

level, and specified positive full-scale, +200 mV (VIN+ − VIN−),

Code 53,248 for the 16-bit level.

Offset Error

Offset is the deviation of the midscale code (Code 32,768 for

the 16-bit level) from the ideal VIN+ − VIN− (that is, 0 V).

Gain Error

This includes both positive full-scale gain error and negative

full-scale gain error. Positive full-scale gain error is the deviation of

the specified positive full-scale code (53,248 for the 16-bit level)

from the ideal VIN+ − VIN− (+200 mV) after the offset error is

adjusted out. Negative full-scale gain error is the deviation of

the specified negative full-scale code (12,288 for the 16-bit

level) from the ideal VIN+ − VIN− (−200 mV) after the offset

error is adjusted out. Gain error includes reference error.

Signal-to-(Noise + Distortion) Ratio

This ratio 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 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

Therefore, for a 12-bit converter, this is 74 dB.

Effective Number of Bits (ENOB)

The ENOB is defined by

ENOB = (SINAD − 1.76)/6.02

Total Harmonic Distortion (THD)

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

fundamental. For the AD7401, it is defined as

THD(dB) = 20 log V2 2 + V32 + V4 2 + V5 2 + V6 2

V1

where:

V1 is the rms amplitude of the fundamental.

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, 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 a

noise peak.

Common-Mode Rejection Ratio (CMRR)

CMRR is defined as the ratio of the power in the ADC output at

±200 mV frequency, f, to the power of a 200 mV p-p sine wave

applied to the common-mode voltage of VIN+ and VIN− of

frequency fS as

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

where:

Pf is the power at frequency f in the ADC output.

PfS is the power at frequency fS in the ADC output.

Power Supply Rejection Ratio (PSRR)

Variations in power supply affect the full-scale transition but

not the converter’s linearity. PSRR is the maximum change in

the specified full-scale (±200 mV) transition point due to a

change in power supply voltage from the nominal value (see

Figure 6).

Isolation Transient Immunity

The isolation transient immunity specifies the rate of rise/fall of

a transient pulse applied across the isolation boundary beyond

which clock or data is corrupted. (It was tested using a transient

pulse frequency of 100 kHz.)

Rev. A | Page 12 of 20

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