Cirrus Logic CS8420 - Manual (Page 80)

80 DS245F4
CS8420
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 35 .
The circuit shown in Figure 36 may be used when external RS422 receivers, optical receivers or other
TTL/CMOS logic outputs drive the CS8420 receiver section.
14.3 Isolating Transformer Requirements
The transformer should be capable of operating from 1.5 to 14 MHz, which is equivalent to an audio data
rate of 25 kHz to 108 kHz after bi-phase mark encoding. Transformers provide isolation from ground loops,
60 Hz noise, and common mode noise and interference. One of the important considerations when choos-
ing transformers is minimizing shunt capacitance between primary and secondary windings. The higher the
shunt capacitance, the lower the isolation between primary and secondary, and the more coupling of high
frequency energy. This energy appears in the form of common mode noise on the receive side ground and
has the potential to degrade analog performance. Therefore, for best performance, shielded transformers
optimized for minimum shunt capacitance should be used. See Application Note 134 for a selection of man-
ufacturers and their part numbers.
RCA Phono
RXP
RXN
CS8420
Coax
75 Ω
75 Ω
0.01 F μ
0.01 F μ
Figure 35. Consumer Input Circuit
RXP
RXN
CS8420
0.01 F μ
0.01 F μ
TTL/CMOS
Gate
Figure 36. TTL/CMOS Input Circuit