LTC2498 Linear Technology, LTC2498 Datasheet - Page 31

• Manufacturer Part Number: LTC2498
• Description: 24-Bit 8-/16-Channel ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
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 22. Input Normal Mode Rejection at f
Figure 21. Input Normal Mode Rejection at DC
–100
–110
–120
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
0
250f
0
N
f
252f
N
INPUT SIGNAL FREQUENCY (Hz)
INPUT SIGNAL FREQUENCY (Hz)
N
2f
N
254f
3f
N
N
256f
4f
N
N
5f
258f
N
f
N
N
6f
= f
N
EOSC/5120
260f
7f
N
N
2498 F21
2498 F22
262f
8f
N
N
S
= 256 • f
N
Figure 24. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (50Hz Notch)
Figure 23. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (60Hz Notch)
Figure 25. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (50Hz/60Hz Notch)
–100
–120
–100
–120
–100
–120
–20
–40
–60
–80
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
0
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
15
20
30
40
45
60
60
75
80
90
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
105 120 135 150 165 180 195 210 225 240
100
120
MEASURED DATA
CALCULATED DATA
MEASURED DATA
CALCULATED DATA
MEASURED DATA
CALCULATED DATA
140
LTC2498
160
180
V
V
V
V
T
V
V
V
V
T
V
V
V
V
T
A
A
CC
REF
IN(CM)
IN(P-P)
A
CC
REF
IN(CM)
IN(P-P)
CC
REF
IN(CM)
IN(P-P)
= 25°C
= 25°C
= 25°C
31
= 5V
= 5V
= 5V
= 5V
= 5V
= 5V
200
= 2.5V
= 2.5V
= 5V
= 2.5V
= 5V
= 5V
2498 F23
2498 F24
2498 F25
2498fc
220