CS8420 CIRRUS [Cirrus Logic], CS8420 Datasheet - Page 71

• Manufacturer Part Number: CS8420
• Description: DIGITAL AUDIO SAMPLE RATE CONVERTER
• Manufacturer: CIRRUS [Cirrus Logic]

ries with each input pin (RXP and RXN) as shown
in Figure 36. However, if a transformer is not used,
high frequency energy could be coupled into the re-
ceiver, causing degradation in analog performance.
Figures 35 and 36 show an optional DC blocking
capacitor (0.1 F to 0.47 F) in series with the ca-
ble input. This improves the robustness of the re-
ceiver, 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 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
DS245PP2
Figure 36. Transformerless Professional Input Circuit
Twisted
Twisted
110
110
Pair
Pair
Figure 35. Professional Input Circuit
XLR
XLR
1
1
±5%. The connector for the con-
* See Text
* See Text
110
110
0.01 F
0.01 F
CS8420
RXP
RXN
CS8420
RXP
RXN
sumer interface is an RCA phono socket. The
receiver circuit for the consumer interface is shown
in Figure 37.
The circuit shown in Figure 38 may be used when
external RS422 receivers, optical receivers or other
TTL/CMOS logic outputs drive the CS8420 receiv-
er section.
15.3 Isolating Transformer Requirements
The transformer should be capable of operating
from 1.5 to 14 MHz, which is equivalent to an au-
dio data rate of 25 kHz to 108 kHz after bi-phase
mark encoding. Transformers provide isolation
from ground loops, 60Hz noise, and common mode
noise and interference. One of the important con-
siderations when choosing transformers is mini-
mizing shunt capacitance between primary and
secondary windings. The higher the shunt capaci-
tance, the lower the isolation between primary and
secondary, and the more coupling of high frequen-
cy energy. This energy appears in the form of com-
mon mode noise on the receive side ground and has
the potential to degrade analog performance.
Therefore, for best performance, shielded trans-
formers optimized for minimum shunt capacitance
should be used. See Application Note 134 for a se-
lection of manufacturers and their part numbers.
Coax
75
TTL/CMOS
Figure 38. TTL/CMOS Input Circuit
Figure 37. Consumer Input Circuit
Gate
RCA Phono
75
0.01 F
0.01 F
0.01 F
0.01 F
CS8420
CS8420
RXP
RXN
RXP
RXN
CS8420
71