ADC10D020 datasheet(13/32 Pages) NSC

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Specification Definitions

APERTURE (SAMPLING) DELAY is that time required after

the fall of the clock input for the sampling switch to open. The

Sample/Hold circuit effectively stops capturing the input sig-

nal and goes into the “hold” mode t

AD after the clock goes

low.

APERTURE JITTER is the variation in aperture delay from

sample to sample. Aperture jitter shows up as input noise.

CLOCK DUTY CYCLE is the ratio of the time that the clock

waveform is high to the total time of one clock period.

CROSSTALK is coupling of energy from one channel into

the other channel.

DIFFERENTIAL NON-LINEARITY (DNL) is the measure of

the maximum deviation from the ideal step size of 1 LSB.

Measured at 20 MSPS with a ramp input.

EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE

BITS) is another method of specifying Signal-to-Noise and

Distortion Ratio, 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 (FPBW) is the frequency at

which the magnitude of the reconstructed output fundamen-

tal drops 3 dB below its 1 MHz value.

GAIN ERROR is the difference between the ideal and actual

differences between the input levels at which the first and

last code transitions occur. That is, how far this difference is

from Full Scale.

INTEGRAL NON LINEARITY (INL) is a measure of the

maximum deviation of each individual code from a line

drawn from zero scale (1⁄2 LSB below the first code transi-

tion) through positive full scale (1⁄2 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. The end

point test method is used. Measured at 20 MSPS with a

ramp input.

INTERMODULATION DISTORTION (IMD) is the creation of

spectral components that are not present in the input as a

result of two sinusoidal frequencies being applied to the ADC

input at the same time. It is defined as the ratio of the power

in the second and third order intermodulation products to the

total power in one of the original frequencies. IMD is usually

expressed in dB.

LSB (LEAST SIGNIFICANT BIT) is the bit that has the

smallest value of weight of all bits. This value is

m * V

REF/2

where “m” is the reference scale factor and “n” is the ADC

resolution, which is 10 in the case of the ADC10D020. The

value of “m” is determined by the logic level at the gain pin

and has a value of 1 when the gain pin is at a logic low and

a value of 2 when the gain pin is at a logic high.

MISSING CODES are those output codes that are skipped

or will never appear at the ADC outputs. These codes cannot

be reached with any input value.

MSB (MOST SIGNIFICANT BIT) is the bit that has the

largest value or weight. Its value is one half of full scale.

OFFSET ERROR is a measure of how far the mid-scale

transition point is from the ideal zero voltage input.

OUTPUT DELAY is the time delay after the rising edge of

the input clock before the data update is present at the

output pins.

OVERRANGE RECOVERY TIME is the time required after

the differential input voltages goes from 1.5V to 0V for the

converter to recover and make a conversion with its rated

accuracy.

PIPELINE DELAY (LATENCY) is the number of clock cycles

between initiation of conversion and when that data is pre-

sented to the output driver stage. New data is available at

every clock cycle, but the data output lags the input by the

Pipelined Delay plus the Output Delay.

POWER SUPPLY REJECTION RATIO (PSRR) can be one

of two specifications. PSRR1 (DC PSRR) is the ratio of the

change in full scale gain error that results from a power

supply voltage change from 2.7V to 3.6V. PSRR2 (AC

PSRR) is measured with a 20 MHz, 250 mV

P-P signal riding

upon the power supply and is the ratio of the signal ampli-

tude on the power supply pins to the amplitude of that

frequency at the output. PSRR is expressed in dB.

SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in

dB, of the rms value of the fundamental signal at the output

to the rms value of the sum of all other spectral components

below one-half the sampling frequency, not including har-

monics or dc.

SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or SI-

NAD) is the ratio, expressed in dB, of the rms value of the

fundamental signal at the output to the rms value of all of the

other spectral components below half the clock frequency,

including harmonics but excluding dc.

SPURIOUS FREE DYNAMIC RANGE (SFDR) is the differ-

ence, expressed in dB, between the rms values of the fun-

damental signal at the output and the peak spurious signal,

where a spurious signal is any signal present in the output

spectrum that is not present at the input.

TOTAL HARMONIC DISTORTION (THD) is the ratio, ex-

pressed in dB, of the rms total of the first 9 harmonic levels

to the level of the input frequency. THD is calculated as

where f

1 is the RMS power of the fundamental (output)

frequency and f

2 through f10 are the RMS power of the first

9 harmonic frequencies in the output spectrum.

ADC10D020 Datasheet(PDF) 13 Page - National Semiconductor (TI)

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