Datasheet

LTC2498
32
2498ff
Figure 23. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (60Hz Notch)
applications inForMation
noise to 15dB (see Figure 22), if noise sources are present
at these frequencies anti-aliasing will reduce their effects.
The user can expect to achieve this level of performance
using the internal oscillator, as shown in Figures 23, 24,
and 25. Measured values of normal mode rejection are
shown superimposed over the theoretical values in all
three rejection modes.
Traditional high order delta-sigma modulators suffer
from potential instabilities at large input signal levels.
The proprietary architecture used for the LTC2498 third
order modulator resolves this problem and guarantees
stability with input signals 150% of full-scale. In many
industrial applications, it is not uncommon to have mi-
crovolt level signals superimposed over unwanted volt
level error sources with several volts of peak-to-peak
Figure 24. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (50Hz Notch)
Figure 21. Input Normal Mode Rejection at DC
Figure 22. Input Normal Mode Rejection at f
S
= 256 • f
N
Figure 25. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (50Hz/60Hz Notch)
INPUT FREQUENCY (Hz)
0
15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240
NORMAL MODE REJECTION (dB)
2498 F23
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
V
IN(P-P)
= 5V
T
A
= 25°C
MEASURED DATA
CALCULATED DATA
INPUT FREQUENCY (Hz)
0
12.5 25 37.5 50 62.5 75 87.5 100 112.5 125 137.5 150 162.5 175 187.5 200
NORMAL MODE REJECTION (dB)
2498 F24
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
V
IN(P-P)
= 5V
T
A
= 25°C
MEASURED DATA
CALCULATED DATA
INPUT FREQUENCY (Hz)
0
20 40 60 80 100 120 140 160 180 200 220
NORMAL MODE REJECTION (dB)
2498 F25
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
V
IN(P-P)
= 5V
T
A
= 25°C
MEASURED DATA
CALCULATED DATA
INPUT SIGNAL FREQUENCY (Hz)
INPUT NORMAL MODE REJECTION (dB)
2498 F21
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
f
N
0 2f
N
3f
N
4f
N
5f
N
6f
N
7f
N
8f
N
f
N
= f
EOSC/5120
INPUT SIGNAL FREQUENCY (Hz)
250f
N
252f
N
254f
N
256f
N
258f
N
260f
N
262f
N
INPUT NORMAL MODE REJECTION (dB)
2498 F22
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120