Si8440/41/42/45

18

Rev. 1.5

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

Figure 5.

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

Figure 6 for more details.

Figure 6. Modulation Scheme

RF

OSCILLATOR

MODULATOR

DEMODULATOR

A

B

Semiconductor-

Based Isolation

Barrier

Transmitter

Receiver

Input Signal

Output Signal

Modulation Signal