Datasheet

LTC2442
22
2442fa
For more information www.linear.com/LTC2442
Table 6. OSR vs Notch Frequency (f
N
) (with Internal Oscillator
Running at 9MHz)
OSR NOTCH (f
N
)
64 28.13kHz
128 14.06kHz
256 7.03kHz
512 3.52kHz
1024 1.76kHz
2048 879Hz
4096 439Hz
8192 220Hz
16384 110Hz
32768* 55Hz
* Simultaneous 50/60Hz rejection
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 LTC2442 significantly
simplifies antialiasing filter requirements.
The LTC2442’s speed/resolution is determined by the
oversample ratio (OSR) of the on-chip digital filter. The
OSR ranges from 64 for 3.5kHz output rate to 32,768 for
6.9Hz (in No Latency mode) output rate. The value of OSR
and the sample rate f
S
determine the filter characteristics
of the device. The first NULL of the digital filter is at f
N
and multiples of f
N
where f
N
= f
S
/OSR, see Figure 10 and
Table 6. The rejection at the frequency f
N
±14% is better
than 80dB, see Figure 11.
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
0
–60
–40
0
180
2442 F10
–80
–100
60 120 240
–120
–140
–20
NORMAL MODE REJECTION (dB)
SINC
4
ENVELOPE
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
47
–140
NORMAL MODE REJECTION (dB)
–130
–120
–110
–100
51 55
59
63
2442 F11
–90
–80
49 53
57
61
Figure 10. Normal Mode Rejection (Internal Oscillator) Figure 11. Normal Mode Rejection (Internal Oscillator)
applications inForMation