CS8420-CS datasheet(80/94 Pages) CIRRUS

80 / 94 page

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

0.01 F

Figure 35. Consumer Input Circuit

RXP

RXN

CS8420

0.01 F

TTL/CMOS

Gate

Figure 36. TTL/CMOS Input Circuit

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