AD7265

Preliminary Technical Data

TERMINOLOGY

Differential Nonlinearity

Track-and-Hold Acquisition Time

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

change between any two adjacent codes in the ADC.

The track-and-hold amplifier returns into track mode after 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.

Integral Nonlinearity

This 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 point 1 LSB

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

above the last code transition.

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 non-fundamental

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:

Offset Error

This applies to Straight Binary output coding. It is the deviation

of the first code transition (00 . . . 000) to (00 . . . 001) from the

ideal, i.e., AGND + 1 LSB.

Offset Error Match

Signal to (Noise + Distortion) = (6.02N + 1.76) dB

This is the worst case difference in Offset Error between any of

the twelve channels.

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

Total Harmonic Distortion

Gain Error

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

harmonics to the fundamental. For the AD7265 it is defined as:

This applies to Straight Binary output coding. It is the deviation

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

ideal (i.e., VREF – 1 LSB) after the offset error has been adjusted

out.

1

2

6

2

5

2

4

2

3

2

2

log

20

)

(

V

V

V

V

V

V

dB

THD

+

+

+

+

=

Gain Error Match

sixth harmonics.

This is the difference in Gain Error between the two channels.

Zero Code Error

Peak Harmonic or Spurious Noise

This applies when using twos complement output coding in

LSB.

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

determined by the largest harmonic in the spectrum, but for

ADCs where the harmonics are buried in the noise floor, it will

be a noise peak.

Zero Code Error Match

This refers to the difference in Zero Code Error between the

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-

channels and determining how much that signal is attenuated in

figure given is the worst-case across all twelve channels for the

AD7265.

Positive Gain Error

This applies when using twos complement output coding in

1 LSB) after the Zero Code Error has been adjusted out.

Rev. PrA | Page 8 of 16