Cirrus Logic CDB5376 - Manual (Page 19)

CDB5376
DS612DB3 19
2.2.2 Differential Amplifiers
The CS3301A/02A amplifiers act as a low-noise gain stage for internal or external differential analog sig-
nals.
2.2.2.1 ACLK Input vs. GUARD Output
By default, channels 1 and 2 of CDB5376 use the CS3301A geophone amplifier while channels 3 and 4
use the CS3302A hydrophone amplifier. The CS3301A amplifier is chopper stabilized and connects pin
13 to a clock source (ACLK) to run the chopper circuitry synchronous to the modulator analog sampling
clock. The CS3302A device is not chopper stabilized (with 1/f noise typically buried below the low-fre-
quency ocean noise) to achieve very high input impedance. To minimize leakage from high-impedance
sensors connected to the CS3302A 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 CS3301A and CS3302A amplifiers, the functionality of pin 13 (ACLK input vs. GUARD out-
put) is the only external difference. CDB5376 can be converted to use any combination of CS3301A and
CS3302A amplifiers by replacing the amplifier device and properly setting the pin 13 jumper (J42, J242,
J342, J442). By default these jumpers are not populated and have shorting traces between pins on the
back side of the PCB. Converting between amplifier types requires carefully cutting the default short and
installing a jumper.
Common amplifier configurations for CDB5376 include 3x or 4x CS3301A amplifiers for land applications,
4x CS3302A amplifiers for marine streamer applications, and 3x CS3301A amplifiers plus 1x CS3302A
amplifier for seabed reservoir monitoring applications. Replacement amplifiers can be requested as sam-
ples from your local Cirrus Logic sales representative.
2.2.2.2 Rough-Fine Outputs - OUTR, OUTF
The analog outputs of the CS3301A/02A differential amplifiers are split into rough-charge and fine-charge
signals for input to the CS5372A
∆Σ modulators. 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 CS3301A/02A amplifiers and into the CS5372A 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- traces.
Analog Signals Description
INA Sensor analog input
INB Test DAC analog input
OUTR, OUTF Analog rough / fine outputs
GUARD CS3302A 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 CS3301A clock input (jumper selection)