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Specification Definitions
APERTURE DELAY
is the time after the falling edge of CS
to when the input signal is acquired or held for conversion.
APERTURE JITTER (APERTURE UNCERTAINTY)
is the
variation in aperture delay from sample to sample. Aperture
jitter manifests itself as noise in the output.
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 speci-
fication 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.
GAIN ERROR
is the deviation of the last code transition
(111...110) to (111...111) from the ideal (V
- 1.5 LSB for
ADCS7476 and ADCS7477, V
REF
- 1 LSB for ADCS7478),
after adjusting for offset error.
INTEGRAL NON-LINEARITY (INL)
is a measure of the
deviation of each individual code from a line drawn from
negative full scale (
1
2
LSB below the first code transition)
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.
INTERMODULATION DISTORTION (IMD)
is the creation of
additional spectral components as a result of two sinusoidal
frequencies being applied to theADC input at the same time.
It is defined as the ratio of the power in the either the two
second order or all four third order intermodulation products
to the sum of the power in both of the original frequencies.
IMD is usually expressed in dBFS.
MISSING CODES
are those output codes that will never
appear at the ADC outputs. The ADCS7476/77/78 is guar-
anteed not to have any missing codes.
OFFSET ERROR
is the deviation of the first code transition
(000...000) to (000...001) from the ideal (i.e. GND + 0.5 LSB
for theADCS7476 andADCS7477, and GND + 1 LSB for the
ADCS7478).
SIGNAL TO NOISE RATIO (SNR)
is the ratio, expressed in
dB, of the rms value of the input signal to the rms value of the
sum of all other spectral components below one-half the
sampling frequency, not including harmonics or dc.
SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD)
Is the ratio, expressed in dB, of the rms value of the input
signal to the rms value of all of the other spectral compo-
nents 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 input
signal 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 dBc, of the rms total of the first five harmonic
levels at the output to the level of the fundamental at the
output. THD is calculated as
where f
1
is the RMS power of the fundamental (output)
frequency and f
2
through f
6
are the RMS power in the first 5
harmonic frequencies.
TOTAL UNADJUSTED ERROR
is a comprehensive speci-
fication which includes gain error, linearity error, and offset
error.
A
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