LTC2483 datasheet(26/32 Pages) LINER

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LTC2483

2483f

lator 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

VREF = 5V, the LTC2483 has a full-scale differential input

range of 5V peak-to-peak. Figures 33 and 34 show mea-

surement 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 situa-

tion. When operating with large input signal levels, the user

must observe that such signals do not violate the device

absolute maximum ratings.

APPLICATIO S I FOR ATIO

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 calculated

curve. Similarly, the measured normal rejection of the

LTC2483 for 50Hz rejection (fEOSC = 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 Input Current section). In this case, the

differential input current cancellation feature of the LTC2483

allows external RC networks without significant degrada-

tion in DC performance.

Traditional high order delta-sigma modulators, while pro-

viding very good linearity and resolution, suffer from

potential instabilities at large input signal levels. The propri-

etary architecture used for the LTC2483 third order modu-

LTC2483 Datasheet(PDF) 26 Page - Linear Technology

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