LT1236A-5 LINER [Linear Technology], LT1236A-5 Datasheet - Page 17

• Manufacturer Part Number: LT1236A-5
• Description: Easy-to-Use, Ultra-Tiny 16-Bit ADC
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Signal Bandwidth and Noise Equivalent Input
Bandwidth
The LTC2450-1 includes a sinc
fi rst notch located at f
signal bandwidth is 26.54Hz. The calculated LTC2450-1
input signal attenuation with frequency at low frequencies
is shown in Figure 18.
The LTC2450-1 input signal attenuation with frequency
over a wide frequency range is shown in Figure 19.
The converter noise level is about 1.4μV
modeled by a white noise source connected at the input
of a noise free converter.
For a simple system noise analysis the V
be modeled as a single pole equivalent circuit character-
ized by a pole location F
If the converter has an unlimited bandwidth or at least
a bandwidth substantially larger than F
Figure 18. Input Signal Attenuation vs Frequency
(Low Frequencies)
–10
–15
–20
–25
–30
–35
–40
–45
–50
–5
0
0
60
INPUT SIGNAL FREQUENCY (Hz)
120
180
0
i
= 60Hz. As such the 3dB input
and a noise spectral density n
240
300
1
360 420
type digital fi lter with the
480
IN
540
i
RMS
24501 F18
drive circuit can
, then the total
600
and can be
i
.
noise contribution of the external drive circuit would be
V
be estimated as the square root of the sum of (V
the square of the LTC2450-1 noise fl oor (≈2μV
Aliasing
The LTC2450-1 signal acquisition circuit is a sampled
data system and as such suffers from input signal alias-
ing. As can be seen from Figure 19, due to the very high
over-sample ratios the high frequency input signal attenu-
ation is reasonably good. Nevertheless a continuous time
antialiasing fi lter connected at the input will preserve
the converter accuracy when the input signal includes
undesirable high frequency components. The antialias-
ing function can be accomplished using the R
components shown in Figure 15 sized such that τ = R
• C
n
IN
= n
> 450ns.
i
Figure 19. Input Signal Attenuation vs Frequency
• √π/2 • F
–100
–20
–40
–60
–80
0
0
i
. Then, the total system noise level can
2.5
INPUT SIGNAL FREQUENCY (MHz)
5.0
7.5
10.0
LTC2450-1
12.5
24501 F19
15.0
2
S
).
and C
17
n
2
) and
24501fb
IN
S