7 Detailed Description

7.1 Overview

ISO7821 employs 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. These devices also incorporates

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 7-1, shows a functional block diagram of a typical channel.

7.2 Functional Block Diagram

TX IN

Oscillator

OOK

Modulation

Transmitter

Emissions

Reduction

Techniques

TX Signal

Conditioning

Envelope

Detection

RX Signal

Conditioning

Receiver

EN

RX OUT

SiO2 based

Capacitive

Isolation

Barrier

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Figure 7-1. Conceptual Block Diagram of a Digital Capacitive Isolator

Also a conceptual detail of how the ON/OFF Keying scheme works is shown in Figure 7-2.

TX IN

RX OUT

Carrier signal through

isolation barrier

Figure 7-2. On-Off Keying (OOK) Based Modulation Scheme

ISO7821, ISO7821F

SLLSEM2H – NOVEMBER 2014 – REVISED NOVEMBER 2024

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