An241 – Cirrus Logic AN241 User Manual
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AN241
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capacitors with a large voltage coefficient (such as general purpose ceramics) since they can degrade
signal linearity.
4. Single-Ended Input Buffer with Dedicated Reference Pins
4.1
Applicable Converters
A single-ended analog input buffer with dedicated reference pins is ideal for use with the following Cirrus
Logic audio converters:
- CS5351
- CS4271
- CS42528/26/18/16 (Note: Full performance will not be realized with a single-ended implementation.)
- CS42428/26/18/16 (Note: Full performance will not be realized with a single-ended implementation.)
4.2
Introduction
A single-ended signal consists of only one signal line and hence requires only one input pin. Some con-
verters have a dedicated reference pin for each channel, as well as an on-chip reference. These pins are
typically labeled VQx. Please check the datsheet for the particular converter to determine the naming con-
vention of the VQx pins.
4.3
Recommended Filter Topology #1
Figure 4 shows a single-ended analog input buffer with dedicated reference pins. This filter implements
one op-amp per channel, and uses a third op-amp to properly bias the analog inputs and independent
channel reference pins. This buffer provides proper biasing, isolation from the switched capacitor cur-
rents, low output impedance, and anti-alias filtering.
Figure 4. Single-Ended Input Buffer with Dedicated Reference Pins (Example #1)
AINL
VQ
in_left
VQ
out
-
+
470 pF
C0G
CSxxxx
634
Ω
91
Ω
2700 pF
C0G
1
µ
F
1
µ
F
100 k
Ω
100 k
Ω
1
µ
F
0.01
µ
F
AINR
2700 pF
C0G
-
+
470 pF
C0G
91
Ω
634
Ω
-
+
VQ
in_right
100 k
Ω
100 k
Ω