CDB5376 Datasheet, PDF (14/78 Pages) Cirrus Logic – Multichannel Seismic Evaluation System

CDB5376
2.2 Analog Hardware
2.2.1 Analog Inputs
2.2.1.1 External Inputs - INA, INB, BNC
External signals into CDB5376 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 CDB5376 through screw terminals on the left side of the PCB. For each chan-
nel (CH1, CH2, CH3, CH4), 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
CH1 INA
CH1 INB
CH2 INA
CH2 INB
CH3 INA
CH3 INB
CH4 INA
CH4 INB
Screw Terminal
J32
J41
J232
J241
J332
J341
J432
J441
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 differential signal traces, with the outer shields connected to ground. The BNC inputs can be connect-
ed to any channel’s INA or INB inputs through the input selection jumpers.
2.2.1.2 GUARD Output, GND Connection
The CS3302 hydrophone amplifier provides a GUARD signal output 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.
By default, the GUARD signal is output to screw terminals on the left side of the PCB for channels 3 and
4, which use the CS3302 amplifier. There is no GUARD signal output for channels 1 and 2 since they use
the CS3301 amplifier, so the GUARD screw terminals for these channels are left floating.
A separate GND connection screw terminal for each channel is also provided if a ground connection to
the sensor cable shield is preferred.
14
DS612DB2