SI8440 SILABS [Silicon Laboratories], SI8440 Datasheet - Page 15

• Manufacturer Part Number: SI8440
• Description: QUAD-CHANNEL DIGITAL ISOLATOR
• Manufacturer: SILABS [Silicon Laboratories]

3. Application Information
3.1. Theory of Operation
The operation of an Si8440 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 Si8440 channel is shown in
Figure 12. A channel consists of an RF transmitter and receiver separated by a transformer.
Referring to the transmitter, input A modulates the carrier provided by an RF oscillator using on/off keying and
applies the resulting waveform to the primary of the transformer. 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.
3.2. Eye Diagram
Figure 13 illustrates an eye-diagram taken on an Si8440-IS. The test used an Anritsu (MP1763C) Pulse Pattern
Generator for the data source. The output of the generator's clock and data from an Si8440-IS were captured on an
oscilloscope. The results illustrate that data integrity was maintained even at the high data rate of 150 Mbps. The
results also show that very low pulse width distortion and very little jitter were exhibited.
A
TRANSMITTER
Figure 12. Simplified Channel Diagram
OSCILLATOR
MODULATOR
RF
Figure 13. Eye Diagram
Rev. 0.3
DEMODULATOR
RECEIVER
Si8440/1/2
B
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