Si8440/41/42/45
2. Functional Description
2.1. Theory of Operation
The operation of an Si844x 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 Si844x channel is shown in
Transmitter
RF
OSCILLATOR
Receiver
A
MODULATOR
Semiconductor-
Based Isolation
Barrier
DEMODULATOR
B
Figure 5. Simplified Channel Diagram
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
Input Signal
Modulation Signal
Output Signal
Figure 6. Modulation Scheme
18
Rev. 1.5
SILABS [ SILICON LABORATORIES ]
