CDB5378 Datasheet, PDF (14/72 Pages) Cirrus Logic – Single-channel Seismic Evaluation System

CDB5378
2.2 Analog Hardware
2.2.1 Analog Inputs
2.2.1.1 External Inputs - INA, INB, BNC
External signals into CDB5378 are from two major classes of sensors, moving coil geophones and piezo-
electric hydrophones. Geophones are low-impedance sensors optimized to measure vibrations in land
applications. Hydrophones are high-impedance sensors optimized to measure pressure in marine appli-
cations. Other sensors for earthquake monitoring and military applications are considered as geophones
for this datasheet.
External signals connect to CDB5378 through screw terminals on the left side of the PCB. These screw
terminals make connections to two external differential inputs, INA and INB. In addition, GND and GUARD
connections are provided for connecting sensor cable shields, if present.
Signal Input
INA
INB
Screw Terminal
J32
J41
Table 7. Screw Terminal Input Connectors
BNC inputs for connecting external signals are not populated during board manufacture, but the empty
PCB footprints exist and can be installed. The inner conductors of the BNC inputs make connections to
the + and - differential signal traces, with the outer shields connected to ground. The BNC inputs can be
connected to the INA or INB inputs through the input selection jumpers.
2.2.1.2 GUARD Output, GND Connection
By default, CDB5378 uses the CS3301 differential geophone amplifier. By replacing the amplifier and
changing the pin 13 signal assignment (J42) it is possible to use the CS3302 hydrophone amplifier in-
stead. The CS3301 amplifier expects an MCLK clock input to pin 13 while the CS3302 amplifier produces
an analog GUARD signal output to pin 13.
The CS3302 hydrophone amplifier analog GUARD signal output is designed to actively drive the cable
shield of a high impedance sensor with the common mode voltage of the sensor differential signal. This
GUARD output on the cable shield minimizes leakage by minimizing the voltage differential between the
sensor signal and the cable shield.
When using the CS3301 amplifier, which does not have a GUARD output, a separate GND screw terminal
is provided for the sensor cable shield. When jumper J42 is set for the CS3301 amplifier the GUARD out-
put screw terminal is left floating.
2.2.1.3 Internal Inputs - DAC_OUT, DAC_BUF
The CS5373A test DAC has two high-performance differential test outputs, a precision output
(DAC_OUT) and a buffered output (DAC_BUF). These test outputs can be connected to the INA or INB
inputs through the input selection jumpers.
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DS639DB3