Much like the break pieces that are used to separate sections of a domino rally, optical isolation is used to separate different sections of an electrical circuit.
Why would you want to separate parts of a circuit? Well, the galvanic isolation provided by an optical isolator can protect sensitive components from potentially damaging high currents or voltages. Such isolation can also be useful for protecting sensors from interference or signal grounding problems.
At the heart of any photocoupler is an optical emitter, such as an LED and a photodetector, tuned to respond to the emitted wavelength. Photocouplers can transmit data incredibly quickly and are ideal for transmitting pulsed, or digital signals.
To provide isolation of an analogue signal, an ordinary optical isolator would require an analogue-to-digital converter (ADC) in front of the emitting LED. If an analogue signal was required on the other side of the isolation barrier, then a digital-to-analogue converter (DAC) would be required at the output of the receiver signal.
Isolation amplifiers integrate the necessary conversion circuitry to allow an analogue signal to be input to the emitter. Broadly speaking, two types of isolation amplifiers are available, that give designers the choice of an analogue output that is directly equivalent to the input signal, or an output that is a digital representation of the input signal.
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