
LTC2492
31
2492fd
Figure 22. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (60Hz Notch)
APPLICATIONS INFORMATION
Traditional high order delta-sigma modulators suffer from
potential instabilities at large input signal levels. The
proprietary architecture used for the LTC2492 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 microvolt level
signals superimposed over unwanted error sources with
several volts of peak-to-peak noise. Figures 25 and 26
show measurement results for the rejection of a 7.5V
peak-to-peak noise source (150% of full scale) applied
to the LTC2492. From these curves, it is shown that the
rejection performance is maintained even in extremely
noisy environments.
INPUT FREQUENCY (Hz)
0
15
30
45
60
75
90
105 120 135 150 165 180 195 210 225 240
NORMAL
MODE
REJECTION
(dB)
2492 F22
0
–20
–40
–60
–80
–100
–120
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
VIN(P-P) = 5V
TA = 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)
2492 F23
0
–20
–40
–60
–80
–100
–120
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
VIN(P-P) = 5V
TA = 25°C
MEASURED DATA
CALCULATED DATA
Figure 23. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (50Hz Notch)
INPUT FREQUENCY (Hz)
0
20
40
60
80
100
120
140
160
180
200
220
NORMAL
MODE
REJECTION
(dB)
2492 F24
0
–20
–40
–60
–80
–100
–120
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
VIN(P-P) = 5V
TA = 25°C
MEASURED DATA
CALCULATED DATA
Figure 24. 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)
2492 F25
0
–20
–40
–60
–80
–100
–120
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
TA = 25°C
VIN(P-P) = 5V
VIN(P-P) = 7.5V
(150% OF FULL SCALE)
Figure 25. Measure Input Normal Mode Rejection vs Input
Frequency with Input Perturbation of 150% (60Hz Notch)
INPUT FREQUENCY (Hz)
0
NORMAL
MODE
REJECTION
(dB)
2492 F26
0
–20
–40
–60
–80
–100
–120
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
TA = 25°C
VIN(P-P) = 5V
VIN(P-P) = 7.5V
(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
Figure 26. Measure Input Normal Mode Rejection vs Input
Frequency with input Perturbation of 150% (50Hz Notch)