General Overview

General Overview
www.vishay.com
Vishay Semiconductors
General Overview of IR Transmission in Free Ambient
Free ambient IR data transmission, IR remote control as well
as most opto-electronic sensors and light barrier systems
work with an optical wavelength between 870 nm and
950 nm. The emitter and detector components are highly
efficient in this near IR wavelength band and can be
manufactured at low cost.
Data transmission in free space demands high interference
immunity of the IR receiving modules. The receiver unit,
waiting to receive signals, is bombarded with different
optical and electromagnetic noise signals, which are
omni-present in the ambient or generated by the electrical
appliance itself. All optical sources with an emission
spectrum in the reception bandwidth (830 nm to 1100 nm)
of the detector can be considered as disturbance sources.
These are mainly fluorescent lamps, incandescent lamps
and sunlight. Many plasma displays can also produce
significant emissions in the optical band of the IR
transmission.
The common method of modulation for IR remote control is
Pulse Code Modulation (PCM). This method of encoding
data enables transmission over long distances using a
receiver with limited bandwidth and good sensitivity.
An emitter for the IR signal with high brightness and
efficiency is also available from Vishay. IR emitters with a
wavelength of 940 nm are the best match for IR receivers
using carrier frequencies between 30 kHz and 56 kHz.
The maximum possible transmission distance of an IR
remote control system depends on various parameters, but
is mainly conditional on the radiant intensity of the emitter
(Ie) and the sensitivity of the receiver (Eemin.). Additionally,
the reflective conditions of the test room, the optical
transmittance of windows or light guides in front of the
receiver and the disturbance conditions influence the
maximum distance obtainable. Of course, also the minimum
possible distance (saturation irradiance) is an important
parameter for a remote control system. The TSOP IR
receiver modules from Vishay will work even with zero
distance between the emitter and the receiver module.
IR transmitter
IR receiver (e.g. TSOP4838)
Irradiance E e
Intensity I e
Distance d
17077
Fig. 1 - Relevant Values for IR Transmission Distance
Calculating transmission ranges in the simplest case
assumes a quadratic relationship between the distance d
and the irradiance of the receiver Ee. Given emitter intensity
Ie, the maximum distance is calculated as:
20169
=
I
E e min.
When the responsivity of the receiver module and the
intensity of the transmitter are known, the transmission
range can either be calculated using this expression or read
from figure 2, where this quadratic equation is shown
graphically. The typical distance shown in the curve was
calculated using a threshold irradiance of 0.12 mW/m2,
which is equivalent to the typical value specified for the
TSOP48 or TSOP22 series. The maximum threshold
sensitivity is specified at 0.25 mW/m2 for these devices,
which is used for calculating the worst case transmission
distance. The typical intensity values of selected emitters
are listed in table 1.
For example, operating a TSAL6200 emitter at 500 mA
pulsed forward current leads to an intensity of 300 mW/sr.
Rev. 1.5, 11-Mar-13
100
e
------------
Max. Receiving Distance (m)
dm ax.
These data result (in combination with the Vishay receiver
module TSOP48xx) in a theoretical transmission range of
50 m (see figure 2).
typical sample in corridor
90
80
70
60
typical sample
in free air
50
40
30
worst case sample in free air
20
Receiving Range of the
IR Receiver Module TSOP4838
10
0
0
100
200
300
400
500
600
700
Radiant Intensity of IR Emitter (mW/sr)
Fig. 2 - Maximum Transmission Range with TSOP4838 as a
Function of the Radiant Intensity of the Emitter
Document Number: 80073
1
For technical questions, contact: [email protected]
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
General Overview
www.vishay.com
Vishay Semiconductors
In practice, the relationship between irradiance and
transmission distance does not exactly follow a quadratic
curve. In most cases, the actual distance is longer than
calculated by the expression. This means that the example
calculated here can be used as a worst case in free air and
in reality better transmission ranges are attained. However,
whenever an opaque window or light pipe is used between
the receiver and the emitter, the actual transmission
distance will be reduced.
Comparisons of remote control systems are often
performed in long corridors. As indicated in figure 2, the
transmission range is increased above the typical distance
under these test conditions because of the reflective
properties of the walls, the ceilings and other objects. Thus
in a corridor, the function of the irradiance vs. distance does
not obey a quadratic expression.
The required levels for transmission optical power in an
enclosed room can be estimated by using other
approximations. If we assume that the whole inner surface
of a room (e.g. floor area of 30 m2, height of 2.5 m) is
irradiated with the emission of an infrared source with an
overall irradiance of Ee = 0.3 mW/m2, then an emitted radiant
flux of 35 mW is necessary (surface = 115 m2, 100 %
efficiency). With an 80 % reflection loss, about 175 mW of
emitted radiation will be required for reliable reception in the
whole room.
175 mW is a value, which can be achieved with an emitter
TSAL6400 operating at a peak forward current of 500 mA.
Under these conditions, no direct path between the emitter
and the receiver is assumed, but that radiation will reach the
detector after at least one reflection. This kind of remote
control system is very user friendly for the customer
because he can aim the handset in any direction of his living
room. An IR emitter with a wide emitting angle will also
provide this kind of comfortable remote control system.
TABLE 1 - EMITTERS FOR TSOP RECEIVER MODULES
EMITTER
PACKAGE WAVELENGTH
DIAMETER
(nm)
RADIANT FLUX
IF = 100 mA
(mW)
typ.
RADIANT INTENSITY
IF = 100 mA
(mW/sr)
typ.
EMISSION
ANGLE
REMARKS
TSAL6100
5 mm
940
35
130
± 10°
T-1¾
TSAL6200
5 mm
940
35
60
± 17°
T-1¾
TSAL6400
5 mm
940
35
40
± 25°
T-1¾
VSLB3940
3 mm
940
40
65
± 22°
T-1
VSML3710
SMD
940
35
8
± 60°
PL-CC-2
VSMB3940
SMD
940
40
13
± 60°
PL-CC-2
VSMB2020
SMD
940
40
40
± 12°
Gullwing
All IR emitting diodes shown in table 1 are suitable for use
with the Vishay IR receivers for standard remote control
applications (30 kHz to 56 kHz).
Rev. 1.5, 11-Mar-13
Document Number: 80073
2
For technical questions, contact: [email protected]
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000