LTC2414/LTC2418

35

241418fa

Traditional high order delta-sigma modulators, while

providing very good linearity and resolution, suffer from

potential instabilities at large input signal levels. The pro-

prietary architecture used for the LTC2414/LTC2418 third

order modulator 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 over volt level perturbations and LTC2414/

LTC2418 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.

has a full-scale differential input range of 5V peak-to-peak.

Figures 39 and 40 show measurement results for the

LTC2414/LTC2418 normal mode rejection ratio with a 7.5V

peak-to-peak (150% of full scale) input signal superim-

posed over the more traditional normal mode rejection

ratio results obtained with a 5V peak-to-peak (full scale)

input signal. In Figure 39, the LTC2414/LTC2418 uses the

and in Figure 40 it uses the internal oscillator with the

LTC2418 rejection performance is maintained with no com-

promises in this extreme situation. When operating with

large input signal levels, the user must observe that such

signals do not violate the device absolute maximum

ratings.

Figure 39. Measured Input Normal Mode Rejection vs Input Frequency with Input Perturbation of 150% Full Scale (60Hz Notch)

Figure 40. Measured Input Normal Mode Rejection vs Input Frequency with Input Perturbation of 150% Full Scale (50Hz Notch)

INPUT FREQUENCY (Hz)

0

15

30

45

60

75

90

105 120 135 150 165 180 195 210 225 240

2414/18 F39

0

–20

–40

–60

–80

–100

–120

SDI = GND

(150% OF FULL SCALE)

INPUT FREQUENCY (Hz)

0

2414/18 F40

0

–20

–40

–60

–80

–100

–120

SDI = GND

(150% OF FULL SCALE)

12.5

25

37.5

50

62.5

75

87.5 100 112.5 125 137.5 150 162.5 175 187.5 200

APPLICATIO S I FOR ATIO