Cirrus Logic CRD5378 - Manual (Page 17)

CRD5378
DS639RD2 17
Analog signal traces out of the CS3301A/02A amplifiers and into the CS5373A modulator 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.
2.2.2.3 Anti-alias RC Filters
The CS5373A
∆Σ modulator is 4th order and high frequency input signals can cause instability. Simple
single-pole anti-alias RC filters are required between the CS3301A/02A amplifier outputs and the
CS5373A modulator inputs to bandwidth limit analog signals into the modulator.
For the CRD5378, the CS3301A/02A amplifier outputs are connected to external 680
Ω
series resistors
and 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.
2.2.3 Delta-Sigma Modulator
The CS5373A
∆Σ modulator performs the A/D function for differential analog signals from the
CS3301A/02A amplifier. The digital output from the modulator is an oversampled
∆Σ bit stream.
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.
Analog Signals Description
INR, INF Modulator analog rough / fine inputs
VREF Voltage reference analog inputs
Digital Signals
Description
MDATA Modulator delta-sigma data output
MFLAG Modulator over-range flag output
MCLK Modulator clock input
MSYNC Modulator synchronization input