si8405 Silicon Laboratories, si8405 Datasheet - Page 14

• Manufacturer Part Number: si8405
• Description: Bidirectional I 2c Isolators With Unidirectional Digital Channels
• Manufacturer: Silicon Laboratories

Si840x
2. Overview
2.1. Theory of Operation
The operation of an Si84xx channel is analogous to that of an opto coupler, except an RF carrier is modulated
instead of light. This simple architecture provides a robust isolated data path and requires no special
considerations or initialization at start-up. A simplified block diagram for a single unidirectional Si84xx channel is
shown in Figure 10.
A channel consists of an RF Transmitter and RF Receiver separated by a semiconductor-based isolation barrier.
Referring to the Transmitter, input A modulates the carrier provided by an RF oscillator using on/off keying. The
Receiver contains a demodulator that decodes the input state according to its RF energy content and applies the
result to output B via the output driver. This RF on/off keying scheme is superior to pulse code schemes as it
provides best-in-class noise immunity, low power consumption, and better immunity to magnetic fields. See
Figure 11 for more details.
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A
Transmitter
OSCILLATOR
MODULATOR
Figure 10. Simplified Channel Diagram
RF
Figure 11. Modulation Scheme
Preliminary Rev. 0.1
Semiconductor-
Based Isolation
Barrier
DEMODULATOR
Modulation Signal
Output Signal
Input Signal
Receiver
B