Datasheet

LTC2483
26
2483fc
The user can expect to achieve this level of performance
using the internal oscillator as it is demonstrated by
Figures 30, 31 and 32. Typical measured values of the
normal mode rejection of the LTC2483 operating with an
external oscillator and a 60Hz notch setting are shown
in Figure 30 superimposed over the theoretical calcu-
lated curve. Similarly, the measured normal rejection
of the LTC2483 for 50Hz rejection (f
EOSC
= 256kHz) and
50Hz/60Hz rejection (internal oscillator) are shown in
Figures 31 and 32.
As a result of these remarkable normal mode specifica-
tions, minimal (if any) antialias filtering is required in front
of the LTC2483. If passive RC components are placed in
front of the LTC2483, the input dynamic current should be
considered (see the Input Current section). In this case,
the differential input current cancellation feature of the
LTC2483 allows external RC networks without significant
degradation in DC performance.
Traditional high order delta-sigma modulators, while pro-
viding very good linearity and resolution, suffer from poten-
tial instabilities at large input signal levels. The proprietary
architecture used for the LTC2483 third order modulator
applicaTions inFormaTion
resolves this problem and guarantees a predictable stable
behavior at input signal levels of up to 150% of full-scale.
In many industrial applications, it is not uncommon to have
to measure microvolt level signals superimposed on volt
level perturbations and the LTC2483 is eminently suited
for such tasks. When the perturbation is differential, the
specification of interest is the normal mode rejection for
large input signal levels. With a reference voltage V
REF
= 5V,
the LTC2483 has a full-scale differential input range of
5V peak-to-peak. Figures 33 and 34 show measurement
results for the LTC2483 normal mode rejection ratio with
a 7.5V peak-to-peak (150% of full-scale) input signal
superimposed over the more traditional normal mode
rejection ratio results obtained with a 5V peak-to-peak
(full-scale) input signal. In Figure 33, the LTC2483 uses
the external oscillator with the notch set at 60Hz and in
Figure 34 it uses the external oscillator with the notch set
at 50Hz. It is clear that the LTC2483 rejection performance
is maintained with no compromises in this extreme situ-
ation. When operating with large input signal levels, the
user must observe that such signals do not violate the
device absolute maximum ratings.