Cirrus Logic CDB5378 - Manual (Page 18)

CDB5378
18 DS639DB4
2.2.1.6 Common Mode Bias
Differential analog signals into the CS3301A/02A amplifiers are required to be biased to the center of the
power supply voltage range, which for bipolar supplies is near ground potential. This common mode bias
voltage is created by buffering the voltage reference, which is nominally +2.5 V relative to the VA- power
supply.
By default, CDB5378 uses the CS3301A differential geophone amplifier and so the common mode bias
resistors on the INA inputs are set for land applications. Marine applications using the CS3302A amplifier
will need to modify the default common mode bias resistors.
Resistors to create the common mode bias are normally selected based on the sensor impedance and
may need to be modified from the CDB5378 defaults depending on the sensor used. Refer to the recom-
mended operating bias conditions for the selected sensor, which are available from the sensor manufac-
turer.
Land Common Mode Filter Specification Value
Common Mode Capacitance 10 nF + 10%
Common Mode Resistance 200
Ω
Common Mode -3 dB Corner @ 6 dB/octave 80 kHz + 10%
Land Differential Filter Specification
Value
Differential Capacitance 10 nF + 10%
Differential Resistance 200
Ω + 200 Ω = 400 Ω
Differential -3 dB Corner @ 6 dB/octave 40 kHz + 10%
Marine Common Mode Filter Specification Value
Hydrophone Group Capacitance 128 nF + 10%
Common Mode Resistance 825 k
Ω || 825 kΩ = 412 kΩ
-3 dB Corner @ 6 dB/octave 3 Hz + 10%
Marine Differential Filter Specification
Value
Differential Capacitance 10 nF + 10%
Differential Resistance 200
Ω + 200 Ω = 400 Ω
-3 dB Corner @ 6 dB/octave 40 kHz + 10%
Specification Value
Geophone Sensor Bias Resistance
20 k
Ω || 20 kΩ = 10 kΩ
Hydrophone Sensor Bias Resistance 18 M
Ω || 18 MΩ = 9 MΩ