6
DEMO MANUAL DC112A
OPERATIO
U
IrDA-4PPM
4Mbps pulse position modulation positions one pulse,
125ns wide in one of four data windows for every data bit
pair. The four data windows make up a bit interval of 500ns
(Figure 5a). By varying the distance from the demo board
0
1
0
0
1
1
0
1
0
1328 F04a
NRZ DATA
IrDA 4PPM HIGH = LIGHT TRANSMITTED
DATA RATES: FIXED AT 4MBAUD
BIT INTERVAL: 500ns
PULSE WIDTH: 1/4 OF INTERVAL OR 125ns
DATA BIT
PAIR
00
01
10
11
4PPM DATA
SYMBOL
1000
0100
0010
0001
RECEIVER
OUTPUT
TRANSMITTER
INPUT
IrDA-4PPM (1m)
IrDA-4PPM (1cm)
RECEIVER
OUTPUT
TRANSMITTER
INPUT
5a
Figure 5. IrDA-4PPM
to the transmitter, the LT1328’s output can be evaluated.
The first photo, Figure 5b, is when the receiver is 1 meter
from the transmitter. The second photo shows the 1cm
response.
5c
5b
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