Datasheet

21
ADC081S021
www.ti.com SNAS308G –APRIL 2005–REVISED MAY 2016
Product Folder Links: ADC081S021
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12 Device and Documentation Support
12.1 Device Support
12.1.1 Device Nomenclature
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. Acquisition time is measured backwards from the falling
edge of CS when the signal is sampled and the part moves from track to hold. The start of the time
interval that contains T
ACQ
is the 13th rising edge of SCLK of the previous conversion when the part
moves from hold to track. The user must ensure that the time between the 13th rising edge of
SCLK and the falling edge of the next CS is not less than T
ACQ
to meet performance specifications.
APERTURE DELAY is the time after the falling edge of CS 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.
CONVERSION TIMEis the time required, after the input voltage is acquired, for the ADC081S021 to convert the
input voltage to a digital word. This is from the falling edge of CS when the input signal is sampled
to the 16th falling edge of SCLK when the SDATA output goes into TRI-STATE.
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 ADC081S021 of this (ENOB) number of bits.
FULL POWER BANDWIDTHis 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 ERRORis the deviation of the last code transition (111...110) to (111...111) from the ideal (V
REF
− 1 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 ADC081S021 input at the same time. It is defined as
the ratio of the power in the second and third order intermodulation products to the sum of the
power in both of the original frequencies. IMD is usually expressed in dB.
MISSING CODES are those output codes that never appear at the ADC081S021 outputs. The ADC081S021 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 (that is,
GND + 1 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 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 components below half the clock
frequency, including harmonics but excluding DC