Cirrus Logic CDB5374 - Manual (Page 16)

CDB5374
16 DS862DB1
2.2.2 Differential Amplifiers
The CS5374 amplifiers act as a low-noise gain stage for internal or external differential analog signals.
2.2.2.1 GUARD Output
The CDB5374 hydrophone amplifiers are 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-imped-
ance sensors connected to the CS5374 amplifier, a GUARD signal output can actively drive a sensor ca-
ble shield with the common mode voltage of the sensor signal.
2.2.2.2 Analog Outputs - OUT
The analog outputs of the CS5374 differential amplifiers are externally split into rough-charge and fine-
charge signals for input to the
∆Σ modulators. Analog signal traces out of the CS5374 amplifiers and into
the 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- trac-
es.
2.2.2.3 Anti-alias RC Filters
The CS5374
∆Σ modulator is 4th order and high-frequency input signals can cause instability. Simple sin-
gle-pole anti-alias RC filters are required between the amplifier outputs and the modulator inputs to band-
width limit analog signals into the modulator.
Analog Signals Description
INA Sensor analog input
INB Test DAC analog input
OUT Analog outputs
GUARD Amplifier guard output
Digital Signals
Description
MUX[0..1] Input mux selection (register bits)
GAIN[0..2] Gain range selection (register bits)
PWDN Power down mode enable (register bit)
Figure 2. RC Filter External Components
INR+
INF+
INF-
INR-
INR+
INF+
INF-
INR-