Cirrus Logic CS8420 - Manual (Page 78)

78 DS245F4
CS8420
14. EXTERNAL AES3/SPDIF/IEC60958 TRANSMITTER AND RECEIVER
COMPONENTS
This section details the external components required to interface the AES3 transmitter and receiver to cables and
fiber-optic components.
14.1 AES3 Transmitter External Components
The output drivers on the CS8420 are designed to drive both the professional and consumer interfaces. The
AES3 specification for professional/broadcast 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 30 , the output of the transformer is short-
circuit protected, has the proper source impedance, and provides a 5 volts 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 specifications 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 31 only uses the TXP pin and provides the proper output imped-
ance and drive level using standard 1% resistors. The connector for a consumer application would be an
RCA phono socket. This circuit is also short circuit protected.
110-(R
TXP
+R
TXN
)
TXP
TXN
XLR
1
CS8420
Figure 30. Professional Output Circuit
374-R
TXP
90.9 Ω
TXP
TXN
RCA
Phono
CS8420
Figure 31. Consumer Output Circuit