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AD9873

Analog Front End Converter for Set-Top Box, Cable Modem

Analog Devices 

AD9873

DEFINITIONS OF TERMS

DIFFERENTIAL NONLINEARITY ERROR (DNL, NO

MISSING CODES)

An ideal converter exhibits code transitions that are exactly 1 LSB

apart. DNL is the deviation from this ideal value. Guaranteed

no missing codes to 10-bit resolution indicates that all 1024 codes

respectively, must be present over all operating ranges.

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 particular code to the true

straight line.

PHASE NOISE

Single-sideband phase noise power density is specified relative to

the carrier (dBc/Hz) at a given frequency offset (1 kHz) from

the carrier. Phase noise can be measured directly in single tone

transmit mode with a spectrum analyzer that supports noise

marker measurements. It detects the relative power between the

carrier and the offset (1 kHz) sideband noise and takes the reso-

lution bandwidth (rbw) into account by subtracting 10 log (rbw).

It also adds a correction factor that compensates for the imple-

mentation of the resolution bandwidth, log display and detector

characteristic.

OUTPUT COMPLIANCE RANGE

The range of allowable voltage at the output of a current-output

DAC. Operation beyond the maximum compliance limits may

cause either output stage saturation, resulting in nonlinear per-

formance or breakdown.

SPURIOUS-FREE DYNAMIC RANGE (SFDR)

The difference, in dB, between the rms amplitude of the DACs

output signal (or ADC’s input signal) and the peak spurious

signal over the specified bandwidth (Nyquist bandwidth unless

otherwise noted).

PIPELINE DELAY (LATENCY)

The number of clock cycles between conversion initiation and the

associated output data being made available.

OFFSET ERROR

First transition should occur for an analog value 1/2 LSB above

negative full scale. Offset error is defined as the deviation of the

actual transition from that point.

APERTURE DELAY

Aperture delay is a measure of the Sample-and-Hold Amplifier

(SHA) performance and specifies the time delay between the

rising edge of the sampling clock input to when the input signal

is held for conversion.

APERTURE UNCERTAINTY (JITTER)

Aperture jitter is the variation in aperture delay for successive

samples and is manifested as noise on the input to the ADC.

SIGNAL-TO-NOISE + DISTORTION (SINAD) RATIO

SINAD is the ratio of the rms value of the measured input signal

to the rms sum of all other spectral components below the Nyquist

frequency, including harmonics but excluding dc. The value for

SINAD is expressed in decibels.

EFFECTIVE NUMBER OF BITS (ENOB)

For a sine wave, SINAD can be expressed in terms of the number

of bits. Using the following formula,

N = (SINAD – 1.76) dB/6.02

it is possible to obtain a measure of performance expressed as N,

the effective number of bits.

SIGNAL-TO-NOISE RATIO (SNR)

SNR is the ratio of the rms value of the measured 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.

TOTAL HARMONIC DISTORTION (THD)

THD is the ratio of the rms sum of the first six harmonic com-

ponents to the rms value of the measured input signal and is

expressed as a percentage or in decibels.

POWER SUPPLY REJECTION

Power supply rejection specifies the converters maximum full-scale

change when the supplies are varied from nominal to minimum

and maximum specified voltages.

CHANNEL-TO-CHANNEL ISOLATION (CROSSTALK)

In an ideal multichannel system, the signal in one channel will

not influence the signal level of another channel. The channel-

to-channel isolation specification is a measure of the change that

occurs to a grounded channel as a full-scale signal is applied to

another channel.

GAIN ERROR

The first code transition should occur at an analog value 1/2 LSB

above negative full scale. The last transition should occur for an

analog value 1 1/2 LSB below the nominal full scale. Gain error

is the deviation of the actual difference between first and last

code transitions and the ideal difference between first and last

code transitions.

–8–

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