SNR = 20log
FSR
RMS
N
RMS
SBAS418I – SEPTEMBER 2007 – REVISED MARCH 2015
The device features unipolar and bipolar analog
9.2 Noise Performance
power supplies (AVDD and AVSS, respectively) for
The ADS1282 offers outstanding noise performance
input range flexibility and a digital supply accepting
(SNR). SNR depends on the data rate, the PGA
1.8V to 3.3V. The analog supplies may be set to +5V
setting. As the bandwidth is reduced by decreasing
to accept unipolar signals (with input offset) or set
the data rate, the SNR improves correspondingly.
lower in the range of ±2.5V to accept true bipolar
Similarly, as the PGA gain is increased, the SNR
input signals (ground referenced).
decreases.
summarizes
the
noise
An internal sub-regulator is used to supply the digital
performance versus data rate and PGA setting.
core from DVDD. The BYPAS pin (pin 28) is the sub-
regulator output and requires a 1
μ
F capacitor for
9.3 Input-Referred Noise
noise reduction. BYPAS should not be used to drive
The input-referred noise is related to SNR by
external circuitry.
:
9.1 ADS1282H
The
H
version of the ADS1282 has an improved input
stage compared to the base version ADS1282. The
where:
ADS1282H design is optimized for use with high
impedance sensors, such as hydrophones. The
FSR
RMS
= Full-scale range RMS = V
REF
/(2 ×
√
2 ×
ADS1282H is recommended when interfacing to
PGA)
hydrophone sensors and can also be used for low-
N
RMS
= Noise RMS (input-referred)
(1)
impedance, geophone sensors as well. The base
version ADS1282 should only be used with low-
9.4 Idle Tones
impedance geophone sensors, where the associated
external terminating resistance is < 50k
Ω
(per
The ADS1282 modulator incorporates an internal
resistor).
dither signal that randomizes the idle tone energy.
Low-level idle tones may still be present, typically
–137dB below full-scale. The low-level idle tones can
be shifted out of the passband with an external offset
= 20mV/PGA. See the
section
for the recommended offset circuit.
Table 1. Signal-to-Noise Ratio (dB)
(1)
PGA
DATA RATE
(SPS)
1
2
4
8
16
32
64
250
130
130
129
128
125
119
114
500
127
127
126
125
122
116
111
1000
124
124
123
122
119
113
108
2000
121
121
120
119
116
111
106
4000
118
118
117
116
113
108
103
(1)
V
IN
= 20mV
DC
/PGA.
12
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