Cirrus Logic CRD5376 - Manual (Page 12)

CRD5376
12 DS612RD2
2.2 Analog Hardware
2.2.1 Analog Inputs
2.2.1.1 External Inputs - INA
External signals into CRD5376 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 CRD5376 through 3-pin headers on the left side of the PCB. For each channel
(CH1, CH2, CH3, CH4), these headers make connections to the differential INA amplifier inputs and to
either a GND or GUARD signal for connection to the sensor cable shields, if present.
2.2.1.2 GUARD Output, GND Connection
The CS3302A 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 pin 3 of the input signal headers on the left side of the PCB for
channels 3 and 4, which use the CS3302A amplifier. There is no GUARD signal output for channels 1 and
2 since they use the CS3301A amplifier, so the GUARD pins for these channels are connected to GND
through 0
Ω jumpers.
2.2.1.3 Internal Inputs - DAC_OUT, DAC_BUF
The CS4373A test DAC has two high performance differential test outputs, a precision output (DAC_OUT)
and a buffered output (DAC_BUF). The DAC_OUT signal is wired directly to the INB inputs of the
CS3301A/02A amplifiers for testing the performance of the electronics channel. The DAC_BUF signal is
wired to the INA inputs of the amplifiers through differential analog switches and is used to test the per-
formance of the measurement channel with a sensor attached.
2.2.1.4 Input Protection
Sensor inputs must have circuitry to protect the analog electronics from voltage spikes. Geophone coils
are susceptible to magnetic fields (especially from lightning) and hydrophones can produce large voltage
spikes if located near an air gun source.
Signal Input Pin Header
CH1 INA J16
CH2 INA J1
CH3 INA J2
CH4 INA J7
Table 4. Pin Header Input Connections