ltc2484 Linear Technology Corporation, ltc2484 Datasheet - Page 34

• Manufacturer Part Number: ltc2484
• Description: 24-bit Delta Sigma Adc With Easy Drive Input Current Cancellation
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC2484
The SINC
mal mode rejection at all frequencies except DC and
integer multiples of the modulator sampling frequency
(f
plify the antialiasing requirements by additional normal
mode signal filtering both in the analog and digital domain.
Independent of the operating mode, f
• f
the maximum output data rate. In the internal oscillator
mode with a 50Hz notch setting, f
50Hz/60Hz rejection, f
setting f
f
is shown in Figures 30 and 31.
34
EOSC
S
OUTMAX
). The LTC2484’s autocalibration circuits further sim-
/20. The performance of the normal mode rejection
S
Figure 32. Input Normal Mode Rejection at DC
–100
–110
–120
4
= 15360Hz. In the external oscillator mode, f
–10
–20
–30
–40
–50
–60
–70
–80
–90
where f
–100
–110
–120
Figure 30. Input Normal Mode Rejection,
Internal Oscillator and 50Hz Notch Mode
digital filter provides greater than 120dB nor-
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
0
0
0 f
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
f
N
S
N
INPUT SIGNAL FREQUENCY (Hz)
2f
U
is the notch frequency and f
2f
S
N
3f
S
S
3f
= 13960Hz and with a 60Hz notch
4f
N
S
U
5f
4f
S
N
6f
S
5f
7f
N
S
8f
6f
W
S
N
9f
S
S
S
10f
7f
= 256 • f
= 12800Hz, with
N
2484 F32
S
11f
2484 F30
8f
S
12f
N
S
U
OUTMAX
N
= 2048
S
is
=
In 1x speed mode, the regions of low rejection occurring
at integer multiples of f
Magnified details of the normal mode rejection curves are
shown in Figure 32 (rejection near DC) and Figure 33
(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
The user can expect to achieve this level of performance
using the internal oscillator as it is demonstrated by Fig-
ures 34, 35 and 36. Typical measured values of the normal
mode rejection of the LTC2484 operating with an internal
oscillator and a 60Hz notch setting are shown in Figure 34
Figure 31. Input Normal Mode Rejection, Internal
Oscillator and 60Hz Notch Mode or External Oscillator
Figure 33. Input Normal Mode Rejection at f
–100
–110
–120
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
250f
0
0
0
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
S
N
f
= 256f
S
252f
INPUT SIGNAL FREQUENCY (Hz)
2f
N
S
3f
254f
N
S
S
) where f
N
4f
have a very narrow bandwidth.
S
256f
5f
S
N
6f
258f
S
7f
N
N
S
represents the notch
8f
260f
S
N
N
9f
2484 F33
2484 F31
value.
S
262f
10f
S
S
N
= 256f
N
2484fa