LTC2492 Linear Technology, LTC2492 Datasheet - Page 30

• Manufacturer Part Number: LTC2492
• Description: 24-Bit 2-/4-Channel ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2492
The SINC
rejection at all frequencies except DC and integer multiples
of the modulator sampling frequency (f
18 and 19). The modulator sampling frequency is f
15,360Hz while operating with its internal oscillator and
f
of frequency F
When using the internal oscillator, the LTC2492 is designed
to reject line frequencies. As shown in Figure 20, rejection
nulls occur at multiples of frequency f
30
S
Figure 18. Input Normal Mode Rejection, Internal Oscillator
and 50Hz Rejection Mode
Figure 19. Input Normal Mode Rejection, Internal Oscillator
and 60Hz Rejection Mode
= F
EOSC
4
/20 when operating with an external oscillator
–100
–110
–120
–100
–110
–120
digital fi lter provides excellent normal mode
–40
–50
–60
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–70
0
0
EOSC
0 f
0
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
S
f
S
.
2f
2f
S
S
3f
S
3f
4f
S
S
4f
5f
S
S
6f
5f
S
S
7f
6f
S
S
8f
7f
S
S
9f
S
8f
10f
S
S
9f
S
11f
N
2492 F18
2492 F19
) (see Figures
S
, where f
S
12f
10f
S
S
N
S
is
=
determined by the input control bits FA and FB (f
or 60Hz or 55Hz for simultaneous rejection). Multiples of
the modulator sampling rate (f
to 15dB (see Figure 21); 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 22, 23,
and 24. Measured values of normal mode rejection are
shown superimposed over the theoretical values in all
three rejection modes.
Figure 21. Input Normal Mode Rejection at f
Figure 20. Input Normal Mode Rejection at DC
–100
–110
–120
–100
–110
–120
–30
–40
–50
–60
–80
–90
–10
–20
–70
–30
–40
–50
–60
–80
–90
–10
–20
–70
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
S
N
= f
N
5f
N
258f
N
• 256) only reject noise
f
N
N
= f
6f
N
EOSC/5120
260f
7f
N
N
2492 F20
2492 F21
S
262f
8f
= 256 • f
N
N
N
= 50Hz
N
2492fb