AD7927 データシートの表示（PDF） - Unspecified

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AD7927

8-Channel, 200 kSPS, 12-Bit ADC with Sequencer in 20-Lead TSSOP

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AD7927

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 LSB

below the first code transition, and full-scale, a point 1 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.

Offset Error

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

(00 . . . 001) from the ideal, i.e., AGND + 1 LSB.

Offset Error Match

This is the difference in offset error between any two channels.

Gain Error

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

(111 . . . 111) from the ideal (i.e., REFIN – 1 LSB) after the

offset error has been adjusted out.

Gain Error Match

This is the difference in gain error between any two channels.

Zero Code Error

This applies when using the twos complement output coding

option, in particular to the 2 ¥ REFIN input range with –REFIN

to +REFIN biased about the REFIN point. It is the deviation of

the midscale transition (all 0s to all 1s) from the ideal VIN volt-

age, i.e., REFIN – 1 LSB.

Zero Code Error Match

This is the difference in Zero Code Error between any two

channels.

Positive Gain Error

This applies when using the twos complement output coding

option, in particular to the 2 ¥ REFIN input range with –REFIN

to +REFIN biased about the REFIN point. It is the deviation of

the last code transition (011. . .110) to (011 . . . 111) from the

ideal (i.e., +REFIN – 1 LSB) after the Zero Code Error has been

adjusted out.

Positive Gain Error Match

This is the difference in Positive Gain Error between any two

channels.

Negative Gain Error

This applies when using the twos complement output coding

option, in particular to the 2 ¥ REFIN input range with –REF IN

to +REFIN biased about the REFIN point. It is the deviation of

the first code transition (100 . . . 000) to (100 . . . 001) from the

ideal (i.e., –REF IN + 1 LSB) after the Zero Code Error has

been adjusted out.

Negative Gain Error Match

This is the difference in Negative Gain Error between any two

channels.

Channel-to-Channel Isolation

Channel-to-Channel Isolation is a measure of the level of crosstalk

between channels. It is measured by applying a full-scale 400 kHz

sine wave signal to all seven nonselected input channels and deter-

mining how much that signal is attenuated in the selected channel

with a 50 kHz signal. The figure is given worst case across all

eight channels for the AD7927.

PSR (Power Supply Rejection)

Variations in power supply will affect the full-scale transition,

but not the converter’s linearity. Power supply rejection is the

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

in power supply voltage from the nominal value. See Typical

Performance Characteristics.

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 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 A/D converter. 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 digiti-

zation 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) = (6.02N + 1.76)dB

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

Total Harmonic Distortion

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

harmonics to the fundamental. For the AD7927, it is defined as:

THD(dB) = 20 log V22 +V32 +V42 +V52 +V62

V1

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.

REV. 0

–7–

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