AN614 Datasheet, PDF (1/10 Pages) Panasonic Semiconductor – Video amplifier, modulator/demodulator IC

AN614
A SIMPLE ALTERNATIVE TO ANALOG ISOLATION AMPLIFIERS
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.
Input
Input
Amp
Modulator
or Driver
ISOLATION
BARRIER
Demodulator
or
Conditioner
Figure 1. ISOamp Block Diagram
Output
Amp
Output
Rev. 0.2 2/13
Copyright © 2013 by Silicon Laboratories
AN614