
AD6652
TERMINOLOGY
Crosstalk
Coupling onto one channel being driven by a (0.5 dBFS) signal
when the adjacent interfering channel is driven by a full-sc
signal. Measurement includes all spurs resulting from both
direct coupling and mixing components.
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ale
uist zones and alias onto itself. IF
y the bandwidth of the input
sam
HA (sample-and-hold amplifier) and clock jitter. (Jitter adds
S
more noise at higher input frequencies.)
g (Oversamp
rs when the
cy components o
ist frequency (F
clo
e sampled
ut frequency b
low th
g inp
ut-of-Range Recovery Time
Out-of-range recovery time is th time it takes for the analog-
to-digital co
transient fro
negative full scale, or from 10% below negative full scale to 10%
below positive full scale.
after a
ove
Processing Gain
When the tuned channel occupies less bandwidth than the
input signal, this rejection of out-of-band noise is referred to as
processing gain
. By using large decimation factors, this process-
ing gain can improve the SNR of the ADC by 20 dB or more.
The following equation can be used to estimate processing gain:
IF Sampling (Undersampling)
Due to the effects of aliasing, an ADC is not necessarily limited
to Nyquist sampling. Frequencies above Nyquist are aliased and
appear in the first Nyquist zone (dc to Sample Rate/2). Care
must be taken to limit the bandwidth of the sampled signal so
that it does not overlap Nyq
pling performance is limited b
Nyquist Samplin
Oversampling occu
analog input signal are be
and requires that the analo
two samples per cycle.
ling)
frequen
e Nyqu
f the
ck
/2),
at least
O
nverter (ADC) to reacquire the analog input
m 10% above positive full scale to 10% ab
=
Bandwidth
Filter
Rate
Sample
_Gain
Processing
_
2
_
log
10
Signal-to-Noise Ratio (SNR)
The ratio of the rms value of the measured input signal to the
rms sum of all other spectral components within the pro-
grammed DDC filter bandwidth, excluding the first six
harmonics
cibels (dB).
de
Two-Tone IMD Rejection
The ratio of the rms value of either input tone to the rms value
of the worst third-order intermodulation product; reported
in dBc.
and dc. The value for SNR is expressed in
ADC EQUIVALENT CIRCUITS
AVDD
0
Figure 35. Analog Input Circuit
AVDD
0
Figure 36. Digital Input
VDD
0
Figure 37. Digital Output