7

LT1328

In situations where long range is not a requirement, a very

simple IR link can be made using unmodulated NRZ

(nonreturn to zero) data. The circuit is shown in Figure 5.

A BER (bit-error rate) transmitter and receiver was used to

test the data-link error rates for data rates of 375kbps.

Because the NRZ data can have long stretches of continu-

ous “1” data, the low frequency corner of the LT1328

photodiode receiver is set to 14Hz to prevent pulse-top

distortion.

To do this, make C1 4.7

µF. This is the only change from

a standard IrDA-SIR receiver. A range of 24" (with a bit

additional processing beyond that provided by the LT1328.

A caution: when using unmodulated data, it is possible to

get a 100% duty cycle on the LED transmitter, so be sure

that the LED can handle this.

Figure 5. Simple NRZ Data Link

5V

24"

R1

100

Ω

R2

10k

R3

3.9

Ω

1/2W

Q3

2N7002

BIT ERROR RATE

TRANSMITTER/RECEIVER

1328 F05

D2

HSDL 4220

OUT

IN

375bps NRZ DATA

1

2

3

4

8

7

6

5

C6

1000pF

LT1328

C4

4.7

µF

C2

4.7

µF

5V

D1

TEMIC

BPV22NF

NC

C5

4.7

µF