Cirrus Logic AN048 - Manual

1
Copyright  Cirrus Logic, Inc. 2003
(All Rights Reserved)
www.cirrus.com
AN48
Application Note
DESIGN NOTES FOR A 2-POLE FILTER WITH
DIFFERENTIAL INPUT
by Steven Green
1. Introduction
Many of today’s Digital-to-Analog Converters
(DACs) require a circuit that has a differential input
and will remove common-mode errors, reduce the
out-of-band noise produced by the delta-sigma
modulator and produce a single-ended output. The
circuit in Figure 1 includes a differential input and a
two-pole analog filter to achieve these design re-
quirements. This application note outlines the de-
sign steps required to select component values.
Notice the similarities between Figure 1 and the
multiple-feedback
low-pass filter shown in
Figure 2. The 2-Pole Low-Pass Filter with Differen-
tial Input is easily designed using the design equa-
tions for the multiple-feedback low-pass filter. Also,
notice the similarities between Figure 1 and
Figure 3. The differential input function is accom-
plished by simply duplicating the component val-
ues generated in the filter design
Figure 1. 2-Pole Low-Pass Filter with Differential Input
R1
C2
C2
R1
R4 R3
R3
R4
C5
C5
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AIN-
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MAR ‘03
AN48REV2