LTC2494CUHF-PBF LINER [Linear Technology], LTC2494CUHF-PBF Datasheet - Page 31

• Manufacturer Part Number: LTC2494CUHF-PBF
• Description: 16-Bit 8-/16-Channel ?? ADC with PGA and Easy Drive Input Current Cancellation
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
In addition to the reference sampling charge, the reference
ESD projection diodes have a temperature dependent leak-
age current. This leakage current, nominally 1nA (±10nA
max) results in a small gain error. A 100Ω reference
resistance will create a 0.5μV full scale error.
Normal Mode Rejection and Anti-aliasing
One of the advantages delta-sigma ADCs offer over
conventional ADCs is on-chip digital fi ltering. Combined
with a large oversample ratio, the LTC2494 signifi cantly
simplifi es anti-aliasing fi lter requirements. Additionally,
the input current cancellation feature allows external low
pass fi ltering without degrading the DC performance of
the device.
The SINC
rejection at all frequencies except DC and integer multiples
of the modulator sampling frequency (f
19 and 20). 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 LTC2494 is designed
to reject line frequencies. As shown in Figure 21, rejec-
tion nulls occur at multiples of frequency f
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 22), if noise sources are present at
these frequencies anti-aliasing will reduce their effects.
S
Figure 19. Input Normal Mode Rejection, Internal Oscillator
and 50Hz Rejection Mode
= F
EOSC
–100
–110
–120
4
–10
–20
–30
–40
–50
–60
–70
–80
–90
/20 when operating with an external oscillator
digital fi lter provides excellent normal mode
0
0 f
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
EOSC
S
2f
S
.
3f
S
4f
S
5f
S
6f
S
S
7f
= f
S
8f
N
S
• 256) only reject noise
9f
S
10f
S
11f
2494 F19
S
S
12f
) (see Figures
N
S
, where f
N
= 50Hz
N
S
is
=
Figure 20. Input Normal Mode Rejection, Internal Oscillator
and 60Hz Rejection Mode
Figure 22. Input Normal Mode Rejection at f
Figure 21. Input Normal Mode Rejection at DC
–100
–110
–120
–100
–110
–120
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
0
250f
0
0
0
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
N
f
f
S
252f
N
INPUT SIGNAL FREQUENCY (Hz)
INPUT SIGNAL FREQUENCY (Hz)
2f
N
2f
S
N
254f
3f
S
3f
N
N
4f
S
256f
4f
5f
N
S
N
6f
5f
258f
S
N
f
N
7f
N
= f
6f
S
N
EOSC/5120
260f
8f
S
7f
N
N
2494 F21
LTC2494
9f
2494 F22
2494 F20
S
262f
8f
10f
N
S
S
N
= 256 • f
31
N
2494fb