lt1328 Linear Technology Corporation, lt1328 Datasheet - Page 6

• Manufacturer Part Number: lt1328
• Description: 4mbps Irda Infrared Receiver
• Manufacturer: Linear Technology Corporation

APPLICATIONS
LT1328
1.152Mbps rate, for example, uses pulses of 217ns for its
bit time of 870ns. Light levels are 100mW/SR to 500mW/
SR over the 1cm to 1 meter range. A photo of a transmit-
ted input and LT1328 output is shown in Figure 3. The
LT1328 output pulse width will be less than 800ns wide
over all of the above conditions at 1.152Mbps. Pin 7
should be held low for these data rates and above.
6
TRANSMITTER
TRANSMITTER
RECEIVER
RECEIVER
OUTPUT
OUTPUT
INPUT
INPUT
IrDA-FIR (1m)
IrDA-4ppm(1m)
DATA BIT
PAIR
00
01
10
11
U
4ppm DATA
SYMBOL
1000
0100
0010
0001
INFORMATION
U
DATA RATES: FIXED AT 4Mbps
BIT INTERVAL: 500ns
PULSE WIDTH: 1/4 OF INTERVAL OR 125ns
DATA RATES: FIXED AT 1.15Mbps
BIT INTERVAL: 870ns
PULSE WIDTH: 1/4 OF INTERVAL OR 217ns
0
0
W
1
1
0
0
Figure 3. IrDA-FIR Modulation
U
0
Figure 4. IrDA-4ppm
0
1
1
1
1
The last IrDA encoding method is for 4Mbps and uses
pulse position modulation, thus its name 4ppm. Two bits
are encoded by the location of a 125ns wide pulse at one
of the four positions within a 500ns interval (2 bits •
1/500ns = 4Mbps). Range and input levels are the same as
for 1.152Mbps. Figure 4 shows the LT1328 reproduction
of this modulation.
TRANSMITTER
TRANSMITTER
RECEIVER
RECEIVER
0
0
OUTPUT
OUTPUT
INPUT
INPUT
1
1
IrDA-FIR (1cm)
IrDA-4ppm (1cm)
0
0
1328 F04a
1328 F03a
NRZ DATA
IrDA 4ppm HIGH = LIGHT TRANSMITTED
NRZ DATA
IrDA-FIR HIGH = LIGHT TRANSMITTED