CDB5378 datasheet(16/72 Pages) CIRRUS

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CDB5378

DS639DB3

2.2.1.6

Common Mode Bias

Differential analog signals into the CS3301/02 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 CS3301 differential geophone amplifier and so the common mode bias re-

sistors on the INA inputs are set for land applications. Marine applications using the CS3302 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

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