LTC1865 LINER [Linear Technology], LTC1865 Datasheet - Page 17

• Manufacturer Part Number: LTC1865
• Description: Ultra-Tiny, Differential, 16-Bit ADC with SPI Interface SPI Interface
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Signal Bandwidth, Transition Noise and Noise
Equivalent Input Bandwidth
The LTC2452 includes a sinc
notch located at f
bandwidth is 26.54Hz. The calculated LTC2452 input signal
attenuation vs frequency over a wide frequency range is
shown in Figure 19. The calculated LTC2452 input signal
attenuation vs frequency at low frequencies is shown in
Figure 20. The converter noise level is about 2.2µV
and can be modeled by a white noise source connected
at the input of a noise-free converter.
On a related note, the LTC2452 uses two separate A/D
converters to digitize the positive and negative inputs.
Each of these A/D converters has 2.2µV
noise. If one of the input voltages is within this small
transition noise band, then the output will fluctuate one
Figure 19. LTC2452 Input Signal Attentuation vs Frequency
–100
–20
–40
–60
–80
0
0
0
2.5
INPUT SIGNAL FREQUENCY (MHz)
= 60Hz. As such, the 3dB input signal
5.0
1
7.5
type digital filter with the first
1.00
1.25
2452 F19
RMS
1.50
transition
RMS
bit, regardless of the value of the other input voltage. If
both of the input voltages are within their transition noise
bands, the output can fluctuate 2 bits.
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
contribution of the external drive circuit would be:
Then, the total system noise level can be estimated as
the square root of the sum of (V
LTC2452 noise floor (~2.2µV
V
n
= n
Figure 20. LTC2452 Input Signal Attenuation
vs Frequency (Low Frequencies)
i
–10
–15
–20
–25
–30
–35
–40
–45
–50
–5
p / 2 • f
0
0
60
INPUT SIGNAL FREQUENCY (Hz)
i
120
180
i
240
and a noise spectral density n
300
2
).
360 420
n
2
) and the square of the
i
, then the total noise
480
IN
LTC2452
540
2452 F20
drive circuit can
600
17
2452fc
i
.