Cirrus Logic CRD5376 - Manual (Page 14)

CRD5376
14 DS612RD2
2.2.1.6 Common Mode Bias
Differential analog signals into the CS3301A/02A amplifiers need to be biased to the center of the power
supply voltage range, which for bipolar supplies is near ground potential. Resistors to create the common
mode bias are selected based on the sensor impedance and may need to be modified from the CRD5376
defaults depending on the sensor to be used. Refer to the recommended operating bias conditions for the
selected sensor, which are available from the sensor manufacturer.
2.2.1.7 Analog Test Switches
Analog switches on CRD5376 connect the DAC_BUF test signal to the sensor. A two stage approach per-
mits flexibility in switch operation while maximizing performance. First, control signals from the digital filter
act as inputs to a 3-to-8 demultiplexer, selecting one of the eight outputs from the decoded GPIO input.
Next, the demultiplexer creates level shifted control signals for the analog switches using the selected out-
put and a pull-up / pull-down circuit on the analog power supplies. These level shifted signals control the
analog switches to connect the test DAC buffered output (DAC_BUF) to the amplifier sensor input (INA).
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 Differential Filter Specification Value
Hydrophone Group Capacitance 128 nF + 10%
Differential Resistance 412 k Ω + 2 kΩ = 414 kΩ
-3 dB Corner @ 6 dB/octave 3 Hz + 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