VISHAY
TSOP348..B
Document Number 84665
Rev. 1.0, 28-Feb-05
Vishay Semiconductors
www.vishay.com
5
Suitable Data Format
The circuit of the TSOP348..B is designed in that way
that unexpected output pulses due to noise or distur-
bance signals are avoided. A bandpass filter, an inte-
grator stage and an automatic gain control are used
to suppress such disturbances.
The distinguishing mark between data signal and dis-
turbance signal are carrier frequency, burst length
and duty cycle.
The data signal should fulfill the following conditions:
• Carrier frequency should be close to center fre-
quency of the bandpass (e.g. 38 kHz).
• Burst length should be 10 cycles/burst or longer.
• After each burst which is between 10 cycles and 70
cycles a gap time of at least 14 cycles is necessary.
• For each burst which is longer than 1.8 ms a corre-
sponding gap time is necessary at some time in the
data stream. This gap time should be at least 4 times
longer than the burst.
• Up to 800 short bursts per second can be received
continuously.
Some examples for suitable data format are: NEC
Code (repetitive pulse), NEC Code (repetitive data),
Toshiba Micom Format, Sharp Code, RC5 Code,
RC6 Code, R-2000 Code, Sony Code.
When a disturbance signal is applied to the
TSOP348..B it can still receive the data signal. How-
ever the sensitivity is reduced to that level that no
unexpected pulses will occur.
Some examples for such disturbance signals which
are suppressed by the TSOP348..B are:
• DC light (e.g. from tungsten bulb or sunlight)
• Continuous signal at 38 kHz or at any other fre-
quency
• Signals from fluorescent lamps with electronic bal-
last with high or low modulation (
see Figure 14 or Figure 15).
Figure 13. Directivity
18549
0.4 0.200.20.4 0.6
0.6
0.9
0°
30°
10°20°
40°
50°
60°
70°
80°
1.0
0.8
0.7
d
rel
-Relative Transmission Distance
Figure 14. IR Signal from Fluorescent Lamp with low Modulation
Figure 15. IR Signal from Fluorescent Lamp with high Modulation
0510 1520
Time ( ms )
16920
IR Signal
IR Signal from fluorescent
lamp with low modulation
0510 1520
Time ( ms )
16921
IR Signal
IR Signal from fluorescent
lamp with high modulation