CS8420 datasheet(70/80 Pages) CIRRUS

70 / 80 page

CS8420

DS245PP2

15. APPENDIX A: EXTERNAL

AES3/SPDIF/IEC60958

TRANSMITTER AND RECEIVER

COMPONENTS

This section details the external components re-

quired to interface the AES3 transmitter and re-

ceiver to cables and fiber-optic components.

15.1

AES3 Transmitter External

Components

The output drivers on the CS8420 are designed to

drive both the professional and consumer interfac-

es. The AES3 specification for professional/broad-

cast use calls for a 110

Ω source impedance and a

balanced drive capability. Since the transmitter

output impedance is very low, a 110

Ω resistor

should be placed in series with one of the transmit

pins. The specifications call for a balanced output

drive of 2-7 volts peak-to-peak into a 110

Ω load

with no cable attached. Using the circuit in

Figure 32, the output of the transformer is short-

circuit protected, has the proper source impedance,

and provides a 5 volt peak-to-peak signal into a

110

Ω load. Lastly, the two output pins should be

attached to an XLR connector with male pins and a

female shell, and with pin 1 of the connector

grounded.

In the case of consumer use, the IEC60958 specifi-

cations call for an unbalanced drive circuit with an

output impedance of 75

Ω and a output drive level

of 0.5 V peak-to-peak ±20% when measured across

a 75

Ω load using no cable. The circuit shown in

Figure 33 only uses the TXP pin and provides the

proper output impedance and drive level using

standard 1% resistors. The connector for a consum-

er application would be an RCA phono socket. This

circuit is also short circuit protected.

The TXP pin may be used to drive TTL or CMOS

gates as shown in Figure 34. This circuit may be

used for optical connectors for digital audio since

they usually have TTL or CMOS compatible in-

puts. This circuit is also useful when driving multi-

ple digital audio outputs since RS422 line drivers

have TTL compatible inputs.

15.2

AES3 Receiver External Components

The CS8420 AES3 receiver is designed to accept

both the professional and consumer interfaces. The

digital 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 im-

pedance, a 110

Ω resistor should be placed across

the receiver terminals to match the line impedance,

as shown in Figure 35. Although transformers are

not required by the AES, they are, however, strong-

ly recommended.

If some isolation is desired without the use of trans-

formers, a 0.01

µF capacitor should be placed in se-

110

Ω

TXP

TXN

XLR

CS8420

Figure 32. Professional Output Circuit

374

Ω

90.9

Ω

TXP

TXN

RCA

Phono

CS8420

Figure 33. Consumer Output Circuit

TXP

TXN

TTL or

CMOS Gate

CS8420

Figure 34. TTL/CMOS Output Circuit

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