Cirrus Logic CS8416 - Manual (Page 49)

DS578F3 49
CS8416
16.EXTERNAL AES3/SPDIF/IEC60958 RECEIVER COMPONENTS
16.1 AES3 Receiver External Components
The CS8416 AES3 receiver is designed to accept both the professional and consumer interfaces. The dig-
ital audio specifications for professional use call for a balanced receiver, using XLR connectors, with
110
Ω ± 20% impedance. The XLR connector on the receiver should have female pins with a male shell.
Since the receiver has a very high input impedance, a 110 Ω resistor should be placed across the receiver
terminals to match the line impedance, as shown in Figures 16 and 17 . Although transformers are not re-
quired by the AES specification, they are strongly recommended.
If some isolation is desired without the use of transformers, a 0.01 μF capacitor should be placed in series
with each input pin (RXP[7:0] and RXN) as shown in Figure 17 . However, if a transformer is not used, high
frequency energy could be coupled into the receiver, causing degradation in analog performance.
Figures 16 and 17 show an optional (recommended) DC blocking capacitor (0.1 μF to 0.47 μF) 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 case of the consumer interface, the standards call for an unbalanced circuit having a receiver imped-
ance of 75
Ω ±5%. The connector for the consumer interface is an RCA phono socket. The receiver circuit
for the consumer interface is shown in Figure 18 . An implementation of the Input S/PDIF Multiplexer using
the consumer interface is shown in Figure 19 .
The circuit shown in Figure 20 may be used when external RS422 receivers, optical receivers or other
TTL/CMOS logic outputs drive the CS8416 receiver section.
In the configuration of systems, it is important to avoid ground loops and DC current flowing down 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 advantageous to have the ground
of two boxes held to the same potential, and the cable shield might be depended upon to make that electrical
connection. Generally, it is a good idea to provide the option of grounding or capacitively coupling the shield
to the chassis.
16.2 Isolating Transformer Requirements
Please refer to the application note AN134: AES and SPDIF Recommended Transformers for resources on
transformer selection.
1
XLR
Twisted
Pair
110 Ω
110 Ω
CS8416
RXP0
RXN
* See Text
1
XLR
Twisted
Pair
110 Ω
110 Ω
CS8416
RXP0
RXN
0.01 F μ
0.01 F μ
* See Text
Figure 16. Professional Input Circuit Figure 17. Transformerless Professional Input Circuit