CDB5376 Datasheet, PDF (18/78 Pages) Cirrus Logic – Multichannel Seismic Evaluation System

CDB5376
2.2.2.3 Anti-alias RC Filters
The CS5372 ∆Σ modulator is 4th order and high-frequency input signals can cause instability. Simple sin-
gle-pole anti-alias RC filters are required between the CS3301/02 amplifier outputs and the CS5372 mod-
ulator inputs to bandwidth limit analog signals into the modulator.
The CS3301/02 amplifier outputs include internal series resistors, so a differential anti-alias RC filter is
created by connecting 20 nF of high-linearity differential capacitance (2x 10 nF C0G) between each half
of the rough and fine signals. External 0-ohm resistors are included in series with the amplifier internal
anti-alias resistors to support testing of other anti-alias RC filter configurations.
INR+
INF+
INF-
INR-
INR+
INF+
INF-
INR-
Figure 2. RC Filter External Components
2.2.3 Delta-Sigma Modulators
A single CS5372 dual modulator performs the A/D function for differential analog signals from two
CS3301/02 amplifiers. The digital outputs are oversampled ∆Σ bit streams.
Analog Signals
INR1, INF1
INR2, INF2
VREF
Digital Signals
MDATA[1..2]
MFLAG[1..2]
MCLK
MSYNC
PWDN[1..2]
OFST
Description
Channel 1 analog rough / fine inputs
Channel 2 analog rough / fine inputs
Voltage reference analog inputs
Description
Modulator delta-sigma data outputs
Modulator over-range flag outputs
Modulator clock input
Modulator synchronization input
Power down mode enable
Internal offset enable (+VD when using CS3301/02)
2.2.3.1 Rough-Fine Inputs - INR, INF
The modulator analog inputs are separated into rough and fine signals, each of which has an anti-alias
RC filter to limit the signal bandwidth into the modulator inputs.
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DS612DB2