TX IN

RX OUT

Carrier signal through

isolation barrier

TX IN

Oscillator

OOK

Modulation

Transmitter

Emissions

Reduction

Techniques

TX Signal

Conditioning

Envelope

Detection

RX Signal

Conditioning

Receiver

EN

RX OUT

Capacitive

Isolation

Barrier

Copyright © 2016, Texas Instruments Incorporated

22

ISO7740, ISO7741, ISO7742

SLLSEP4A – MARCH 2016 – REVISED JUNE 2016

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Product Folder Links: ISO7740 ISO7741 ISO7742

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Copyright © 2016, Texas Instruments Incorporated

8 Detailed Description

8.1 Overview

The ISO774x family of devices have an ON-OFF keying (OOK) modulation scheme to transmit the digital data

across a silicon dioxide based isolation barrier. The transmitter sends a high frequency carrier across the barrier

to represent one digital state and sends no signal to represent the other digital state. The receiver demodulates

the signal after advanced signal conditioning and produces the output through a buffer stage. If the ENx pin is

low then the output goes to high impedance. The ISO774x devices also incorporate advanced circuit techniques

to maximize the CMTI performance and minimize the radiated emissions due the high frequency carrier and IO

buffer switching. The conceptual block diagram of a digital capacitive isolator, Figure 19, shows a functional

block diagram of a typical channel.

8.2 Functional Block Diagram

Figure 19. Conceptual Block Diagram of a Digital Capacitive Isolator

Figure 20 shows a conceptual detail of how the ON/OFF keying scheme works.

Figure 20. On-Off Keying (OOK) Based Modulation Scheme