Aes3 Receiver External Components; Isolating Transformer Requirements; Figure 25. Professional Input Circuit; Figure 26. Transformerless Professional Input Circuit - Cirrus Logic Crystal CS8427 Series Preliminary Product Information

13.2 AES3 Receiver External Components

The CS8427 AES3 receiver is designed to accept
both the professional and consumer interfaces. The
digital audio specifications for professional use call
for a balanced receiver, using XLR connectors,
with 110Ω ±20% impedance. The XLR connector
on the receiver should have female pins with a male
shell. Since the receiver has a very high input im-
pedance, a 110Ω resistor should be placed across
the receiver terminals to match the line impedance,
as shown in Figure 25. Although transformers are
not required by the AES, they are, however, strong-
ly recommended.
If some isolation is desired without the use of trans-
formers, a 0.01µF capacitor should be placed in se-
ries with each input pin (RXP and RXN) as shown
in Figure 26. However, if a transformer is not used,
high frequency energy could be coupled into the re-
ceiver, causing degradation in analog performance.
Figures 25 and 26 show an optional DC blocking
capacitor (0.1µF to 0.47µF) in series with the cable
input. This improves the robustness of the receiver,
preventing the saturation of the transformer, or any
DC current flow, if a DC voltage is present on the
cable.
In the configuration of systems, it is important to
avoid ground loops and DC current flowing down
XLR
* See Text
110 Ω
110 Ω
Twisted
Pair
1

Figure 25. Professional Input Circuit

RCA Phono
75 Ω
75 Ω
Coax

Figure 27. Consumer Input Circuit

50
CS8427
µ
0.01 F
RXP
µ
0.01 F
RXN
CS8427
µ
0.01 F
RXP
RXN
µ
0.01 F
the shield of the cable that could result when boxes
with different ground potentials are connected.
Generally, it is good practice to ground the shield
to the chassis of the transmitting unit, and connect
the shield through a capacitor to chassis ground at
the receiver. However, in some cases it is advanta-
geous to have the ground of two boxes held to the
same potential, and the cable shield might be de-
pended upon to make that electrical connection.
Generally, it may be a good idea to provide the op-
tion of grounding or capacitively coupling the
shield to the chassis.
In the case of the consumer interface, the standards
call for an unbalanced circuit having a receiver im-
pedance of 75 Ω ±5%. The connector for the con-
sumer interface is an RCA phono socket. The
receiver circuit for the consumer interface is shown
in Figure 27.
The circuit shown in Figure 28 may be used when
external RS422 receivers, optical receivers or other
TTL/CMOS logic outputs drive the CS8427 receiv-
er section.

13.3 Isolating Transformer Requirements

Please refer to the application note AN134: "AES
and SPDIF Recommended Transformers" for re-
sources on transformer selection.
XLR
* See Text
110 Ω
110 Ω
Twisted
Pair
1

Figure 26. Transformerless Professional Input Circuit

TTL/CMOS
Gate

Figure 28. TTL/CMOS Input Circuit

CS8427
CS8427
µ
0.01 F
RXP
µ
0.01 F
RXN
CS8427
µ
0.01 F
RXP
RXN
µ
0.01 F
DS477PP1