CS

90%

10%

90%

10%

90%

10%

SCLK

CS

1

2

ADC122S655

www.ti.com

SNAS445A – FEBRUARY 2008 – REVISED MARCH 2013

Figure 5. Valid CS Assertion Times

Specification Definitions

APERTURE DELAY is the time between the fourth falling edge of SCLK and the time when the input signal is

acquired or held for conversion.

COMMON MODE REJECTION RATIO (CMRR) is a measure of how well in-phase signals common to both input

pins are rejected.

To calculate CMRR, the change in output offset is measured while the common mode input voltage is changed

from 2V to 3V.

CMRR = 20 LOG (

Δ Output Offset / Δ Common Input)

(1)

CONVERSION TIME is the time required, after the input voltage is acquired, for the ADC to convert the input

voltage to a digital word.

DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1

LSB.

DUTY CYCLE is the ratio of the time that a repetitive digital waveform is high to the total time of one period. The

specification here refers to the SCLK.

EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise

and Distortion or SINAD. ENOB is defined as (SINAD

− 1.76) / 6.02 and says that the converter is equivalent to

a perfect ADC of this (ENOB) number of bits.

FULL POWER BANDWIDTH is a measure of the frequency at which the reconstructed output fundamental

drops 3 dB below its low frequency value for a full scale input.

INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from

negative full scale (½ LSB below the first code transition) through positive full scale (½ LSB above the last code

transition). The deviation of any given code from this straight line is measured from the center of that code value.

MISSING CODES are those output codes that will never appear at the ADC outputs. The ADC122S655 is

specified not to have any missing codes.

NEGATIVE FULL-SCALE ERROR is the difference between the differential input voltage at which the output

code transitions from negative full scale to the next code and

NEGATIVE GAIN ERROR is the difference between the negative full-scale error and the offset error.

OFFSET ERROR is the difference between the differential input voltage at which the output code transitions from

code 000h to 001h and 1/2 LSB.

POSITIVE FULL-SCALE ERROR is the difference between the differential input voltage at which the output

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