AD7484 Analog Devices, AD7484 Datasheet - Page 11
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AD7484
Manufacturer Part Number
AD7484
Description
14-Bit, 3 MSPS SAR ADC
Manufacturer
Analog Devices
Datasheet
1.AD7484.pdf
(20 pages)
Specifications of AD7484
Resolution (bits)
14bit
# Chan
1
Sample Rate
3MSPS
Interface
Par
Analog Input Type
SE-Uni
Ain Range
Uni 2.5V
Adc Architecture
SAR
Pkg Type
QFP
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TERMINOLOGY
Integral Nonlinearity
The integral nonlinearity is the maximum deviation from a
straight line passing through the endpoints of the ADC transfer
function. The endpoints of the transfer function are zero scale, a
point 1/2 LSB below the first code transition, and full scale, a
point 1/2 LSB above the last code transition.
Differential Nonlinearity
The differential nonlinearity is the difference between the
measured and ideal 1 LSB change between any two adjacent
codes in the ADC.
Offset Error
The offset error is the deviation of the first code transition
(00…000) to (00…001) from the ideal, that is, AGND + 0.5 LSB.
Gain Error
The gain error is the deviation of the last code transition
(111…110) to (111…111) from the ideal, that is, V
after the offset error has been adjusted out.
Track-and-Hold Acquisition Time
The track-and-hold acquisition time is the time required for the
output of the track-and-hold amplifier to reach its final value,
within ±1/2 LSB, after the end of conversion (the point at which
the track-and-hold returns to track mode).
Signal-to-Noise + Distortion (SINAD) Ratio
The SINAD ratio is the measured ratio of signal-to-noise +
distortion at the output of the ADC. The signal is the rms ampli-
tude of the fundamental. Noise is the sum of all nonfundamental
signals up to half the sampling frequency (f
ratio is dependent on the number of quantization levels in the
digitization process; the more levels, the smaller the quantization
noise. The theoretical SINAD ratio for an ideal N-bit converter
with a sine wave input is given by
Therefore, this is 86.04 dB for a 14-bit converter.
Signal-to-Noise + Distortion = (6.02N + 1.76)dB
S
/2), excluding dc. The
REF
− 1.5 LSB,
Rev. C | Page 11 of 20
Total Harmonic Distortion (THD)
The THD is the ratio of the rms sum of the harmonics to the
fundamental. It is defined as
where V
V
sixth harmonics.
Peak Harmonic or Spurious Noise
The peak harmonic or spurious noise is the ratio of the rms
value of the next largest component in the ADC output spectrum
(up to f
The value of this specification is usually determined by the
largest harmonic in the spectrum, but for ADCs where the
harmonics are buried in the noise floor, it is a noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities creates distortion
products at sum and difference frequencies of mfa ± nfb, where
m and n = 0, 1, 2, 3, and so on. Intermodulation distortion
terms are those for which neither m nor n is equal to zero. For
example, the second order terms include (fa + fb) and (fa − fb),
whereas the third order terms include (2fa + fb), (2fa − fb), (fa +
2fb), and (fa − 2fb).
The AD7484 is tested using the CCIF standard where two input
frequencies near the top end of the input bandwidth are used.
In this case, the second order terms are usually distanced in
frequency from the original sine waves, whereas the third order
terms are usually at a frequency close to the input frequencies.
As a result, the second order and third order terms are specified
separately. The calculation of the intermodulation distortion is
as per the THD specification, where it is the ratio of the rms
sum of the individual distortion products to the rms amplitude
of the sum of the fundamentals expressed in dBs.
4
, V
THD
5
, and V
S
/2 and excluding dc) to the rms value of the fundamental.
1
is the rms amplitude of the fundamental and V
( )
dB
6
are the rms amplitudes of the second through the
=
20
log
V
2
2
+
V
3
2
+
V
V
1
4
2
+
V
5
2
+
V
6
AD7484
2
2
, V
3
,