REV. 0

AD7664

–7–

Pin

No.

Mnemonic

Type

Description

35

CNVST

DI

Start Conversion. A falling edge on

CNVST puts the internal sample/hold into the hold state and

initiates a conversion. In impulse mode (IMPULSE HIGH and WARP LOW), if

CNVST is

held low when the acquisition phase

(t

hold state and a conversion is immediately started.

36

AGND

P

Must Be Tied to Analog Ground.

37

REF

AI

Reference Input Voltage.

38

REFGND

AI

Reference Input Analog Ground.

39

INGND

AI

Analog Input Ground.

43

IN

AI

NOTES

AI = Analog Input

DI = Digital Input

DI/O = Bidirectional Digital

DO = Digital Output

P = Power

DEFINITION OF SPECIFICATIONS

INTEGRAL NONLINEARITY ERROR (INL)

Linearity error refers to the deviation of each individual code

from a line drawn from “negative full scale” through “positive full

scale.” The point used as “negative full 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 code to the true straight line.

DIFFERENTIAL NONLINEARITY ERROR (DNL)

In an ideal ADC, code transitions are 1 LSB apart. Differential

nonlinearity is the maximum deviation from this ideal value. It is

often specified in terms of resolution for which no missing codes

are guaranteed.

FULL-SCALE ERROR

The last transition (from 011 . . . 10 to 011 . . . 11 in two’s

complement coding) should occur for an analog voltage 1 1/2 LSB

below the nominal full scale (2.49994278 V for the 0 V–2.5 V

range). The full-scale error is the deviation of the actual level of

the last transition from the ideal level.

UNIPOLAR ZERO ERROR

The first transition should occur at a level 1/2 LSB above analog

ground (19.073

µV for the 0 V–2.5 V range). Unipolar zero error is

the deviation of the actual transition from that point.

SPURIOUS FREE DYNAMIC RANGE (SFDR)

The difference, in decibels (dB), between the rms amplitude of

the input signal and the peak spurious signal.

EFFECTIVE NUMBER OF BITS (ENOB)

ENOB is a measurement of the resolution with a sine wave

input. It is related to S/(N+D) by the following formula:

and is expressed in bits.

TOTAL HARMONIC DISTORTION (THD)

THD is the ratio of the rms sum of the first five harmonic

components to the rms value of a full-scale input signal and is

expressed in decibels.

SIGNAL-TO-NOISE RATIO (SNR)

SNR is the ratio of the rms value of the actual input signal to the

rms sum of all other spectral components below the Nyquist

frequency, excluding harmonics and dc. The value for SNR is

expressed in decibels.

SIGNAL TO (NOISE + DISTORTION) RATIO

(S/[N+D])

S/(N+D) is the ratio of the rms value of the actual input signal

to the rms sum of all other spectral components below the

Nyquist frequency, including harmonics but excluding dc. The

value for S/(N+D) is expressed in decibels.

APERTURE DELAY

Aperture delay is a measure of the acquisition performance and

is measured from the falling edge of the

CNVST input to when

the input signal is held for a conversion.

TRANSIENT RESPONSE

The time required for the AD7664 to achieve its rated accuracy

after a full-scale step function is applied to its input.

OVERVOLTAGE RECOVERY

The time required for the ADC to recover to full accuracy after

an analog input signal 150% of full-scale is reduced to 50% of

the full-scale value.