REV. 0

AD9845A

–7–

DEFINITIONS OF SPECIFICATIONS

DIFFERENTIAL NONLINEARITY (DNL)

An ideal ADC exhibits code transitions that are exactly 1 LSB

apart. DNL is the deviation from this ideal value. Thus every code

must have a finite width. No missing codes guaranteed to 12-bit

resolution indicates that all 4096 codes, respectively, must be

present over all operating conditions.

PEAK NONLINEARITY

Peak nonlinearity, a full signal chain specification, refers to the

peak deviation of the output of the AD984x from a true straight

line. The point used as “zero scale” occurs 1/2 LSB before the

first code transition. “Positive full scale” is defined as a Level 1,

1/2 LSB beyond the last code transition. The deviation is measured

from the middle of each particular output code to the true straight

line. The error is then expressed as a percentage of the 2 V ADC

full-scale signal. The input signal is always appropriately gained up

to fill the ADC’s full-scale range.

TOTAL OUTPUT NOISE

The rms output noise is measured using histogram techniques.

The standard deviation of the ADC output codes is calculated

in LSB, and represents the rms noise level of the total signal

chain at the specified gain setting. The output noise can be

converted to an equivalent voltage, using the relationship 1 LSB

= (ADC Full Scale/2

ADC. For the AD9845A, 1 LSB is 500 µV.

POWER SUPPLY REJECTION (PSR)

The PSR is measured with a step change applied to the supply

pins. This represents a very high frequency disturbance on the

AD984x’s power supply. The PSR specification is calculated

from the change in the data outputs for a given step change in

the supply voltage.

INTERNAL DELAY FOR SHP/SHD

The internal delay (also called aperture delay) is the time delay

that occurs from when a sampling edge is applied to the AD984x

until the actual sample of the input signal is held. Both SHP and

SHD sample the input signal during the transition from low to

high, so the internal delay is measured from each clock’s rising

edge to the instant the actual internal sample is taken.

EQUIVALENT INPUT CIRCUITS

330

DVDD

DVSS

Figure 1. Digital Inputs—SHP, SHD, DATACLK, CLPOB,

CLPDM, HD, VD, PBLK, SCK, SL

DVDD

DVSS

DRVSS

DRVDD

THREE-

STATE

DATA

DOUT

Figure 2. Data Outputs—D0–D11

60

ACVDD

ACVSS

ACVSS

Figure 3. CCDIN (Pin 30)

330

DVDD

DVSS

DVDD

DVSS

DVSS

DATA IN

RNW

DATA OUT

Figure 4. SDATA (Pin 47)