Rev. 0.2 2/13

Copyright © 2013 by Silicon Laboratories

AN614

AN614

1. Introduction

Analog circuits sometimes require linear (analog) signal isolation for safety, signal level shifting, and/or ground loop

elimination. Linear signal isolation is typically difficult to implement, costly, and often exhibits mediocre

performance. While the design community thirsts for a flexible and inexpensive linear isolator solution, it is the

analog isolation amplifier (ISOamp) that most often captures the socket.

ISOamps are hybridized devices that contain linear input and output circuits separated by an internal isolation

barrier. ISOamps typically modulate the linear input signal and transmit the resulting digital information across the

isolation barrier to a demodulator where it is converted back to analog (Figure 1). ISOamps typically employ

transformers and high-voltage capacitors or optocouplers in the isolation barrier design. While ISOamps are a

convenient single-package linear isolation solution, the industry's limited device offerings often force the designer

to make difficult trade-offs or add external circuitry for a complete solution. In addition, transformer-based ISOamps

are susceptible to signal corruption from external field interference and errors due to poor common-mode transient

immunity (CMTI). Optocoupler-based ISOamp versions also often suffer from poor linearity and even worse CMTI.

This application note provides insight into a robust linear isolator reference design based on the Silicon Labs

Si86xx family of CMOS digital isolators.

Figure 1. ISOamp Block Diagram

Modulator

or Driver

ISOLATION

BARRIER

Demodulator

or

Conditioner

Input 

Amp

Output 

Amp

Input

Output