LTC2452_11 Datasheet, PDF (17/22 Pages) Linear Technology – Ultra-Tiny, Differential, 16-Bit ADC with SPI Interface SPI Interface

LTC2452
APPLICATIONS INFORMATION
Signal Bandwidth, Transition Noise and Noise
Equivalent Input Bandwidth
The LTC2452 includes a sinc¹ type digital filter with the first
notch located at f₀ = 60Hz. As such, the 3dB input signal
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_RMS
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_RMS transition
noise. If one of the input voltages is within this small
transition noise band, then the output will fluctuate one
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_IN drive circuit can
be modeled as a single-pole equivalent circuit character-
ized by a pole location f_i and a noise spectral density n_i.
If the converter has an unlimited bandwidth, or at least a
bandwidth substantially larger than f_i, then the total noise
contribution of the external drive circuit would be:
V_n = n_i p / 2 • f_i
Then, the total system noise level can be estimated as
the square root of the sum of (V_n2) and the square of the
LTC2452 noise floor (~2.2µV²).
0
–20
–40
–60
–80
–100
0
2.5 5.0 7.5 1.00 1.25 1.50
INPUT SIGNAL FREQUENCY (MHz)
2452 F19
Figure 19. LTC2452 Input Signal Attentuation vs Frequency
0
–5
–10
–15
–20
–25
–30
–35
–40
–45
–50
0 60 120 180 240 300 360 420 480 540 600
INPUT SIGNAL FREQUENCY (Hz)
2452 F20
Figure 20. LTC2452 Input Signal Attenuation
vs Frequency (Low Frequencies)
2452fc
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