CDB5378 datasheet(14/72 Pages) CIRRUS

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CDB5378

DS639DB3

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.

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.

Signal Input

Screw Terminal

INA

J32

INB

J41

Table 7. Screw Terminal Input Connectors

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