Document Number: 82575

www.vishay.com

Revision 17-August-01

2

Figure 1. Block Diagram

Theory of operation

The IRMS6118/IRMT6118 Slimline—Infrared Data Transceiver

consists of a detector photodiode, an IR LED transmitter, an IC

containing ambient light suppressor, and Automatic Gain control

circuitry (AGC).

cal) at

5.0 V of DC ambient signal. This will typically allow opera-

tion in all but direct sunlight.

The AGC in the IC is to keep the system output constant by

varying the gain to accommodate a wide range of input signals.

It also provides noise immunity in the high noise ambient envi-

ronment.

For normal operation of the transmit and receiver modes, the

Shut Down (SD) pin should be held low. It is recommended

that this pin be connected to GND if Shut Down (SD) mode is

not used.

In receive mode, the receiver output (RxD) which normally

stays high, will go low for duration of the receive pulses. It is a

push-pull CMOS driver capable of driving a standard CMOS or

TTL load. No external pull-up or pull-down resistor is required.

turn on IR LED transmitter. At the LED Anode (pin 1) connect

reduce the thermal dissipation and to lower LED current.

+

-

+

-

Receiver Output

Receive

Detector

Regulated

Voltage &

Current

Sources

Power Down

Current Limited

Transmit

Error

amp

Detector

Reference

Lowpass

Filter

IR LED

AGC & Signal

Reference

Processor

AGC

Tx

Blanking

Switched

current source

Tx In

Tx Input

Buffer

Main

amp

Pre

amp

Ambient DC

Cancelling

LED Anode

Receive Ouput

Blanking

TxD

SD

RxD

Tri-State

Control

Tri-State

CMOS Buffer

Driver

GND

500 k

Ω

Differential

Photodiode

500 k

Ω

Pin 3

Pin 8

Pin 6

Pin 4

Pin 5

Pin 1

LED Cathode

Pin 2

Table 2. Slimline IRMS6118/IRMT6118 Truth Table

Inputs

Outputs

SD

TxD

Detector

RxD

LED

2.4 V to

5.0 V

High X=don’t care

state

X=don’t care

state

500 k

Ω

pull-up

Off

2.4 V to

5.0 V

Low

High

Undefined On

Low

<0.4

High

Off

<4.0

Low