HSDL-3208-S21 Datasheet, PDF (19/22 Pages) Lite-On Technology Corporation – Ultra Small Profile Package IrDA® Data Compliant Low Power 115.2 kbit/s Infrared Transceiver

Appendix D:
Window Designs for
HSDL-3208
Optical port dimensions for
HSDL-3208:
To ensure IrDA compliance, some
constraints on the height and width
of the window exist. The minimum
dimensions ensure that the IrDA
cone angles are met without
vignetting. The maximum
dimensions minimize the effects of
stray light. The minimum size
corresponds to a cone angle of 30°
and the maximum size corresponds
to a cone angle of 60°.
In the figure below, X is the width
of the window, Y is the height of
the window and Z is the distance
from the HSDL-3208 to the back of
the window. The distance from the
center of the LED lens to the
center of the photodiode lens, K, is
5.1 mm. The equations for
computing the window dimensions
are as follows:
X = K + 2*(Z + D)*tanA
Y = 2*(Z + D)*tanA
The above equations assume that
the thickness of the window is
negligible compared to the
distance of the module from the
back of the window (Z). If they are
comparable, Z' replaces Z in the
above equation. Z' is defined as
Z' = Z + t/n
where ‘t’ is the thickness of the
window and ‘n’ is the refractive
index of the window material.
The depth of the LED image inside
the HSDL-3208, D, is 3.17 mm.
‘A’ is the required half angle for
viewing. For IrDA compliance, the
minimum is 150 and the maximum
is 300. Assuming the thickness of
the window to be negligible, the
equations result in the following
tables and graphs:
OPAQUE
MATERIAL
IR TRANSPARENT WINDOW
;;;;;;;; _Y
;;;;;^;_{;;;;;;;;;;;;;;;;;;; X}
IR TRANSPARENT
;; ^;;;;;^;; ^WINDOW
K
OPAQUE
MATERIAL
Z
A
D
Figure 27. Window design diagram.
19