Receiver

The receiver consists of two
channels, Rxd-A (2.4-115.2 kb/s)
and Rxd-B (0.5-4 Mb/s). Both
channels use the same detector
and pre-amplifier stage. Both
channels use CX1, CX5, CX6, and
R3 to filter out power supply noise.
The Rxd-B channel uses an
adaptive threshold circuit to
minimize pulse width distortion
(PWD) over the IrDA required
dynamic range. The Rxd-B
channel also uses a squelch circuit
to eliminate noise bits on Rxd
when no Ir signal is present. The
adaptive threshold circuit makes
use of CX3 and CX4.
In general, 2.4-115.2 kb/s Ir signals
create output pulses on Rxd-A, and
0.5-4 Mb/s Ir signals create output
pulses on Rxd-B. However, Ir
signals in the 10 kHz - 1 MHz range
may appear on both Rxd-A and
Rxd-B, depending on the Ir signal
strength. The presense of signal at
both Rxd-A and Rxd-B should not
be a problem for any properly
designed I/O chip. The I/O chip
should be designed to look at only
one channel at a time, depending
upon which data mode has been
selected by the software.