Datasheet

13
LTC1415
APPLICATIONS INFORMATION
WUU
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4.096V to 2.048V and shifts the common mode voltage
from half of full scale to 2.274V.
AC Coupled Inputs
The analog inputs can be AC coupled for applications
where the input has no DC information. The input of the
ADC does need to be DC biased at midscale. Figures 10d
and 10e demonstrate AC coupling and the required bias-
ing. Figure 10d shows the ADC with a full scale of 4.096V,
a common mode voltage of 2.048V and an input that
swings from 0V to 4.096V. This circuit has the lowest
noise (SINAD = 72dB to 100kHz) but will have distortion
INPUT FREQUENCY (Hz)
SIGNAL/(NOISE + DISTORTION) (dB)
80
70
60
50
40
30
20
10
0
1k 100k 1M 2M
LTC1415 • F10a
10k
Figure 10a. CMRR vs Input Frequency Figure 10b. Shifting the Input Range Up from Ground by 200mV
LTC1415
+A
IN
ANALOG INPUT
1.25V TO 3.298V
–A
IN
V
REF
REFCOMP
AGND
LTC1415 • F10c
1
2
3
4
5
10µF
24Ω
1µF
V
OUT
= 1.2V
LT1004-1.2
Figure 10c. 2.048V Input Range with a Common Mode
Voltage of 2.274V. For Low Distortion AC Applications
LTC1415
+A
IN
ANALOG INPUT
4.096V
P-P
–A
IN
V
REF
REFCOMP
AGND
LTC1415 • F10d
1
2
3
4
5
10µF
2k
2k
Figure 10d. 4.096V
P-P
Input Range with AC Coupling.
For Low Noise AC Applications
LTC1415
+A
IN
ANALOG INPUT
2.048V
P-P
–A
IN
V
REF
REFCOMP
AGND
LTC1415 • F10e
1
2
3
4
5
10µF
1µF
25Ω
1k
9k
1k
–
+
LT1004-1.2
Figure 10e. 2.048V
P-P
Input Range with AC Coupling. For Low Distortion AC Applications
LTC1415
+A
IN
ANALOG INPUT
0.2V TO 4.296V
–A
IN
V
REF
REFCOMP
AGND
LTC1415 • F10b
1
2
3
4
5
10µF
R2
3.9k
R1
200Ω