Cirrus Logic CS8415A - Manual (Page 36)

36 DS470F4
CS8415A
13.APPENDIX A: EXTERNAL AES3/SPDIF/IEC60958 RECEIVER
COMPONENTS
13.1 AES3 Receiver External Components
The CS8415A 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 Figure 11 . Although transformers are not required by the AES,
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 (RXP0 and RXN0) as shown in Figure 12 . However, if a transformer is not used, high-
frequency energy could be coupled into the receiver, causing degradation in analog performance.
Figures 11 and 12 show an optional 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 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 may be a good idea to provide the option 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 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 13 . Figure 14 shows an implementation of the input S/PDIF
multiplexer using the consumer interface.
The circuit shown in Figure 15 may be used when external RS422 receivers, optical receivers or other
TTL/CMOS logic outputs drive the CS8415A receiver section.