CDB5378 datasheet(17/72 Pages) CIRRUS

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CDB5378

DS639DB3

2.2.2

Differential Amplifiers

The CS3301/02 amplifiers act as a low-noise gain stage for internal or external differential analog signals.

2.2.2.1

MCLK Input vs. GUARD Output

By default, CDB5378 uses the CS3301 geophone amplifier which is chopper stabilized. The CS3301 con-

nects pin 13 to a clock source (MCLK) to run the chopper circuitry synchronous to the modulator analog

sampling clock. The CS3302 hydrophone amplifier is 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-impedance sensors connected to the CS3302 amplifier, pin 13 produces a GUARD signal output to

actively drive a sensor cable shield with the common mode voltage of the sensor signal.

Comparing the CS3301 and CS3302 amplifiers, the functionality of pin 13 (MCLK input vs. GUARD out-

put) is the only external difference. CDB5378 can be converted to use either the CS3301 or CS3302 by

replacing the amplifier device and properly setting the pin 13 jumper (J42). By default this jumper is not

populated and has a shorting trace between pins on the back side of the PCB. Converting between am-

plifier types requires carefully cutting the default short and installing a jumper. A replacement amplifier

can be requested as a sample from your local Cirrus Logic sales representative.

2.2.2.2

Rough-Fine Outputs - OUTR, OUTF

The analog outputs of the CS3301/02 differential amplifiers are split into rough-charge and fine-charge

signals for input to the CS5373A

∆Σ modulator. The amplifier outputs include integrated series resistors

to create the anti-alias RC filters required to limit the modulator input signal bandwidth.

Analog signal traces out of the CS3301/02 amplifiers and into the CS5373A modulator 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- traces.

2.2.2.3

Anti-alias RC Filters

The CS5373A

∆Σ modulator is 4th order and high-frequency input signals can cause instability. Simple

single-pole anti-alias RC filters are required between the CS3301/02 amplifier outputs and the CS5373A

modulator inputs to bandwidth limit analog signals into the modulator.

Analog Signals

Description

INA

Sensor analog input

INB

Test DAC analog input

OUTR, OUTF

Analog rough / fine outputs

GUARD

CS3302 guard output (jumper selection)

Digital Signals

Description

MUX[0..1]

Input mux selection

GAIN[0..2]

Gain range selection

PWDN

Power down mode enable

CLK

CS3301 clock input (jumper selection)

CDB5378 Datasheet(PDF) 17 Page - Cirrus Logic

CDB5378 Datasheet(HTML) 17 Page - Cirrus Logic

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