Datasheet

2
1f
2
6f
2
2f
10
‡
A
A++A
log20=THD

ADC78H89
www.ti.com SNAS201D –APRIL 2003–REVISED MARCH 2013
Specification Definitions
ACQUISITION TIME is the time required to acquire the input voltage. That is, it is time required for the hold
capacitor to charge up to the input voltage.
APERTURE DELAY is the time between the fourth falling SCLK edge of a conversion and the time when the
input signal is acquired or held for conversion.
CONVERSION TIME is the time required, after the input voltage is acquired, for the ADC to convert the input
voltage to a digital word.
CROSSTALK is the coupling of energy from one channel into the other channel, or the amount of signal energy
from one analog input that appears at the measured analog input.
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
specification 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
REF
- 1.5
LSB), 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 (½ LSB below the first code transition) through positive full scale (½ 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 the ADC input at the same time. It is defined as the ratio of the power in
the both 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 ADC78H89 is ensured
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).
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 d.c.
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 components below half the clock frequency, including
harmonics but excluding d.c.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, 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, expressed in dB, expressed in dB or dBc, of the rms total
of the first five harmonic components at the output to the rms level of the input signal frequency as seen at the
output. THD is calculated as
(1)
where A
f1
is the RMS power of the input frequency at the output and A
f2
through A
f6
are the RMS power in the
first 5 harmonic frequencies.
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