CS8414 View Datasheet(PDF) - Unspecified
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CS8414 Datasheet PDF : 38 Pages
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CS8413 CS8414
APPENDIX A: RS422 RECEIVER
INFORMATION
The RS422 receivers on the CS8413 and CS8414
are designed to receive both the professional and
consumer interfaces, and meet all specifications
listed in the digital audio standards. Figure A20 il-
lustrates the internal schematic of the receiver por-
tion of both chips. The receiver has a differential
input. A Schmitt trigger is incorporated to add hys-
teresis which prevents noisy signals from corrupt-
ing the phase detector.
Professional Interface
The digital audio specifications for professional
use call for a balanced receiver, using XLR connec-
tors, with 110Ω ±20% impedance. (The XLR con-
nector on the receiver should have female pins with
a male shell.) Since the receiver has a very high im-
pedance, a 110Ω resistor should be placed across
the receiver terminals to match the line impedance,
as shown in Figure A21, and, since the part has in-
ternal biasing, no external biasing network is need-
ed. If some isolation is desired without the use of
transformers, a 0.01µF capacitor should be placed
on the input of each pin (RXP and RXN) as shown
in Figure A22. However, if transformers are not
used, high frequency energy could be coupled be-
tween transmitter and receiver causing degradation
in analog performance.
16kΩ 8kΩ
9 RXP
10 RXN
16kΩ 4kΩ
8kΩ
+
-
4kΩ
Figure 20. RS422 Receiver Internal Circuit
Although transformers are not required by AES
they are strongly recommended. The EBU requires
transformers. Figures A21 and A22 show an op-
tional DC blocking capacitor on the transmission
line. A 0.1 to 0.47µF ceramic capacitor may be
used to block any DC voltage that is accidentally
connected to the digital audio receiver. The use of
this capacitor is an issue of robustness as the digital
audio transmission line does not have a DC voltage
component.
Grounding the shield of the cable is a tricky issue.
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 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-
XLR
110Ω
Twisted
Pair
1
* See Text
110Ω
CS8413/14
RXP
RXN
Figure 21. Professional Input Circuit
XLR
110Ω
Twisted
Pair
1
* See Text
110Ω
0.01 µF
CS8413/14
RXP
0.01 µF
RXN
Figure 22. Transformerless Professional Circuit
34
DS240F1
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