Application Specific Transmitter Design:

Transmitter Drive
The infrared LED in the HSDL-
1100 is driven by signals present
at TXD. See Figure 3.
The IrDA physical layer specification
requires trise and tfall of the
transmitted optical signal at
4 Mb/s to be 40 ns or less. The
HSDL-1100 budgets 30 ns of trise
and tfall for the LED, and 10 ns
for trise and tfall of the electrical
ILED pulse. In order to reach
< 30 ns trise and tfall for the LED,
a peaking circuit of R1 and CX2 is
CX5 CX1 DC - DC
CONVERTER
MAIN GROUND
GROUND
PLANE ISLAND
>3 cm
Figure 2.
RLED
HSDL-1100
CX7
CX2
R1
10
TXD
7
Figure 3.
TXD PULSE HSDL-1100 PIN 7 OPTICAL ILED PULSE
VIH