Introduction
With the growing popularity and possibilities of digital recording,
new problems arise, such as system interconnectivity. For digital
audio signals, the Sony/Philips Digital Interface Format (S/PDIF)
is most often used. This standard defines both the logical layer
(i.e. how the information is coded) and the physical layer (i.e.
how the signals are electrically or optically transmitted).
Both a professional as a consumer derivation of the S/PDIF standard
exists. The latter is often found on consumer electronics, such as
Compact Disc (CD), MiniDisc (MD), Digital Compact Cassette (DCC)
and Digital Audio Tape (DAT) recorders and players. More recently,
computer multimedia hardware, such as soundcards or CD-ROM players,
also support S/PDIF input and output.
Problem
Although many of the S/PDIF signals are present (at the logical
layer level), they are not always available in the right way (at
the physical, electrical layer). For example, computer hardware
often has the S/PDIF signals available in CMOS compatible signal
levels via (jumper) headers. In order to meet the S/PDIF physical
layer specifications, line drivers are needed.
Solutions
In fig. 1 an optical line driver is given for Toslink (optical
fiber connection) cables. It gets power from 5 Volts power source,
which is available in most devices. The S/PDIF must be at CMOS
or TTL compatible level. (The coaxial flavor implementation
may be added later.)
fig. 1. Toslink optical output line driver circuitry schematics