CDB5376 Datasheet, PDF (17/78 Pages) Cirrus Logic – Multichannel Seismic Evaluation System

CDB5376
2.2.2 Differential Amplifiers
The CS3301/02 amplifiers act as a low-noise gain stage for internal or external differential analog signals.
Analog Signals
INA
INB
OUTR, OUTF
GUARD
Description
Sensor analog input
Test DAC analog input
Analog rough / fine outputs
CS3302 guard output (jumper selection)
Digital Signals
MUX[0..1]
GAIN[0..2]
PWDN
CLK
Description
Input mux selection
Gain range selection
Power down mode enable
CS3301 clock input (jumper selection)
2.2.2.1 ACLK Input vs. GUARD Output
By default, channels 1 and 2 of CDB5376 use the CS3301 geophone amplifier while channels 3 and 4
use the CS3302 hydrophone amplifier. The CS3301 amplifier is chopper stabilized and connects pin 13
to a clock source (ACLK) to run the chopper circuitry synchronous to the modulator analog sampling clock.
The CS3302 device is not chopper stabilized (with 1/f noise typically buried below the low-frequency
ocean noise) to achieve very high input impedance. To minimize leakage from high-impedance sensors
connected to the CS3302 amplifier, pin 13 produces a GUARD signal output to actively drive a sensor
cable shield with the common mode voltage of the sensor signal.
Comparing the CS3301 and CS3302 amplifiers, the functionality of pin 13 (ACLK input vs. GUARD output)
is the only external difference. CDB5376 can be converted to use any combination of CS3301 and
CS3302 amplifiers by replacing the amplifier device and properly setting the pin 13 jumper (J42, J242,
J342, J442). By default these jumpers are not populated and have shorting traces between pins on the
back side of the PCB. Converting between amplifier types requires carefully cutting the default short and
installing a jumper.
Common amplifier configurations for CDB5376 include 3x or 4x CS3301 amplifiers for land applications,
4x CS3302 amplifiers for marine streamer applications, and 3x CS3301 amplifiers plus 1x CS3302 ampli-
fier for seabed reservoir monitoring applications. Replacement amplifiers can be requested as samples
from your local Cirrus Logic sales representative.
2.2.2.2 Rough-Fine Outputs - OUTR, OUTF
The analog outputs of the CS3301/02 differential amplifiers are split into rough-charge and fine-charge
signals for input to the CS5372 ∆Σ modulators. The amplifier outputs include integrated series resistors
to create the anti-alias RC filters required to limit the modulator input signal bandwidth.
Analog signal traces out of the CS3301/02 amplifiers and into the CS5372 modulators are 4-wire
INR+ / INF+ / INF- / INR- quad groups, and are routed with INF+ and INF- as a traditional differential pair
and INR+ and INR- as guard traces outside the respective INF+ and INF- traces.
DS612DB2
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