LTC2411 LINER [Linear Technology], LTC2411 Datasheet - Page 31

• Manufacturer Part Number: LTC2411
• Description: 24-Bit No Latency ADC with Differential Input and Reference in MSOP
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Figure 32 (rejection near DC) and Figure 33 (rejection at
f
These curves have been derived for the external oscillator
mode but they can be used in all operating modes by
appropriately selecting the f
The user can expect to achieve in practice this level of
performance using the internal oscillator as it is demon-
strated by Figures 34 to 36. Typical measured values of the
normal mode rejection of the LTC2411 operating with an
internal oscillator and a 60Hz notch setting are shown in
Figure 34 superimposed over the theoretical calculated
curve. Similarly, typical measured values of the normal
mode rejection of the LTC2411 operating with an internal
oscillator and a 50Hz notch setting are shown in Figure 35
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 LTC2411/LTC2411-1. If passive RC components
are placed in front of the LTC2411/LTC2411-1, 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
potential instabilities at large input signal levels. The pro-
prietary architecture used for the LTC2411/LTC2411-1
third order modulator resolves this problem and guaran-
tees a predictable stable behavior at input signal levels of
S
= 256f
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
N
Figure 32. Input Normal Mode Rejection
) where f
0
0
f
N
INPUT SIGNAL FREQUENCY (Hz)
U
2f
N
N
represents the notch frequency.
3f
N
U
4f
N
N
value.
5f
N
6f
W
N
7f
N
2411 F32
8f
N
U
–100
–120
–100
–120
–20
–40
– 60
–80
– 60
–20
–40
–80
0
0
0
0
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240
Figure 33. Input Normal Mode Rejection
250f
0
Figure 34. Input Normal Mode Rejection
vs Input Frequency (LTC2411)
25
Figure 35. Input Normal Mode Rejection
vs Input Frequency (LTC2411)
N
LTC2411/LTC2411-1
252f
INPUT SIGNAL FREQUENCY (Hz)
50
N
254f
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
N
75
256f
MEASURED DATA
CALCULATED DATA
MEASURED DATA
CALCULATED DATA
N
100
258f
N
125
260f
N
2411 F33
262f
150
N
V
V
V
V
F
T
V
V
V
V
F
T
O
A
CC
REF
INCM
IN(P-P)
O
A
CC
REF
INCM
IN(P-P)
= 5V
= 25 C
175
= GND
= 25 C
= 5V
= 5V
= 5V
= 5V
= 2.5V
31
= 2.5V
= 5V
2411 F34
= 5V
2411 F35
200