LTC2413 LINER [Linear Technology], LTC2413 Datasheet - Page 33

• Manufacturer Part Number: LTC2413
• Description: 24-Bit No Latency ADC, with Simultaneous 50Hz/60Hz Rejection
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Normal Mode Rejection and Antialiasing
One of the advantages delta-sigma ADCs offer over con-
ventional ADCs is on-chip digital filtering. Combined with
a large oversampling ratio, the LTC2413 significantly
simplifies antialiasing filter requirements.
The sinc
mode rejection at all frequencies except DC and integer
multiples of the modulator sampling frequency (f
LTC2413’s autocalibration circuits further simplify the
antialiasing requirements by additional normal mode sig-
nal filtering both in the analog and digital domain. Inde-
pendent of the operating mode, f
f
OUTMAX
4
where f
digital filter provides greater than 120dB normal
Figure 39. Input Normal Mode Rejection
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
0
N
in the notch frequency and f
f
U
N
INPUT SIGNAL FREQUENCY (Hz)
2f
N
U
3f
N
4f
N
5f
S
N
W
= 256 • f
6f
N
7f
Figure 38. Input Normal Mode Rejection
N
2413 F39
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
8f
0
N
N
0
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
U
OUTMAX
= 2048 •
f
S
S
). The
2f
S
3f
is
S
4f
S
5f
the maximum output data rate. In the internal oscillator
mode, f
f
The combined normal mode rejection performance is
shown in Figure 38. The regions of low rejection occurring
at integer multiples of f
Magnified details of the normal mode rejection curves are
shown in Figure 39 (rejection near DC) and Figure 40
(rejection at f
frequency. These curves have been derived for the exter-
nal oscillator mode but they can be used in all operating
modes by appropriately selecting the f
EOSC
S
6f
S
/10.
7f
S
S
8f
= 13980Hz. In the external oscillator mode, f
S
Figure 40. Input Normal Mode Rejection
9f
–100
–110
–120
2413 F38
–10
–20
–30
–40
–50
–60
–70
–80
–90
S
S
10f
0
250f
= 256f
S
F
F
f
N
EOSC
O
O
= LOW OR
= EXTERNAL OSCILLATOR,
252f
INPUT SIGNAL FREQUENCY (Hz)
= 10 • f
N
N
S
) where f
254f
S
have a very narrow bandwidth.
N
256f
N
N
258f
represents the notch
N
N
260f
LTC2413
value.
N
2413 F40
262f
N
sn2413 2413fs
33
S
=