LTC2412IGN datasheet(32/36 Pages) LINER

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LTC2412

2412f

APPLICATIO S I FOR ATIO

Figure 36 (rejection at fS = 256fN) where fN represents the

notch frequency. These curves have been derived for the

external oscillator mode but they can be used in all

operating modes by appropriately selecting the fN value.

The user can expect to achieve in practice this level of

performance using the internal oscillator as it is demon-

strated by Figures 37 and 38. Typical measured values of

the normal mode rejection of the LTC2412 operating with

an internal oscillator and a 60Hz notch setting are shown

in Figure 37 superimposed over the theoretical calculated

curve. Similarly, typical measured values of the normal

mode rejection of the LTC2412 operating with an internal

oscillator and a 50Hz notch setting are shown in Figure 38

superimposed over the theoretical calculated curve.

As a result of these remarkable normal mode specifica-

tions, minimal (if any) antialias filtering is required in front

of the LTC2412. If passive RC components are placed in

front of the LTC2412, the input dynamic current should be

considered (see Input Current section). In cases where

large effective RC time constants are used, an external

buffer amplifier may be required to minimize the effects of

dynamic input current.

Traditional high order delta-sigma modulators, while pro-

viding very good linearity and resolution, suffer from po-

tential instabilities at large input signal levels. The

proprietary architecture used for the LTC2412 third order

modulator resolves this problem and guarantees a pre-

dictable stable behavior at input signal levels of up to 150%

INPUT SIGNAL FREQUENCY (Hz)

2412 F35

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

2fN 3fN 4fN 5fN 6fN 7fN 8fN

INPUT SIGNAL FREQUENCY (Hz)

250fN 252fN 254fN 256fN 258fN 260fN 262fN

2412 F36

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

Figure 35. Input Normal Mode Rejection

Figure 36. Input Normal Mode Rejection

Figure 37. Input Normal Mode Rejection vs Input Frequency

with Input Perturbation of 100% Full Scale (60Hz Notch)

INPUT FREQUENCY (Hz)

105 120 135 150 165 180 195 210 225 240

2412 F37

–20

–40

–60

–80

–100

–120

VCC = 5V

REF+ = 5V

REF – = GND

VINCM = 2.5V

VIN(P-P) = 5V

FO = GND

TA = 25°C

MEASURED DATA

CALCULATED DATA

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