STA120D View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
STA120D Datasheet PDF : 15 Pages
| |||
STA120
APPENDIX A: RS422 RECEIVER INFORMATION
The RS422 receivers on the STA120 is designed to receive both the professional and consumer interfac-
es, and meet all specifications listed in the digital audio standards. Figure 6 illustrates the internal sche-
matic of the receiver portion of both chips. The receiver has a differential input. A Schmitt trigger is
incorporated to add hysteresis which prevents noisy signals from corrupting the phase detector.
Figure 6. RS422 Receiver Internal Circuit
RXP
RXN
1K
ix
1K
K-ix
D98AU983
Professional Interface
The digital audio specifications for professional use call for a balanced receiver, using XLR connectors,
with 110Ω ±20% impedance. (The XLR connector on the receiver should have female pins with a male
shell.) Since the receiver has a very high impedance, a 110Ω resistor should be placed across the receiv-
er terminals to match the line impedance, as shown in figure 7, and, since the part has internal biasing,
no external biasing network is needed. If some isolation is desired without the use of transformers, a
0.01µF capacitor should be placed on the input of esch pin (RXP and RXN) as shown in Figure 8. How-
ever, if transformers are not used, high frequency energy could be coupled between transmitter and re-
ceiver causing degradation in analog performance.
Although transformers are not required by AES they are strongly recommended. The EBU requires trans-
formers. Figure 7 and 8 show an optional DC blocking capacitor on the transmission line. A 0.1 to 0.47µF
ceramic capacitor may be used to block any DC voltage that is accidentally connected to the digital audio
receiver. The use of this capacitor is an issue of robustness s the digital audio transmission line does not
have a DC voltage component.
Figure 7. Professional Input Circuit
XLR
110Ω
TWISTED
PAIR
1
(*)See Text
RXP
110Ω
RXN
D98AU984A
Figure 8. Transformerless Professional Circuit
XLR
110Ω
TWISTED
PAIR
1
(*)See Text 0.01µF
RXP
110Ω
0.01µF
RXN
D98AU985A
12/15
Share Link: 