LTC2452
17
2452fd
For more information www.linear.com/LTC2452
applicaTions inForMaTion
Signal Bandwidth, Transition Noise and Noise
Equivalent Input Bandwidth
The LTC2452 includes a SINC
1
type digital filter with the first
notch located at f
0
= 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, regard-
less 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
n
2
) and the square of the
LTC2452 noise floor (~2.2µV
2
).
Figure 19. LTC2452 Input Signal Attenuation vs Frequency Figure 20. LTC2452 Input Signal Attenuation
vs Frequency (Low Frequencies)
INPUT SIGNAL FREQUENCY (MHz)
0
INPUT SIGNAL ATTENUATION (dB)
–40
1.00 1.25 1.50
2452 F19
–60
–80
–20
–100
2.5
5.0 7.5
INPUT SIGNAL FREQUENCY (Hz)
0
INPUT SIGNAL ATTENUATIOIN (dB)
–20
–10
480
2452 F20
–30
–40
–25
–15
–5
–35
–45
–50
12060
240180
360 420 540
300
600
