What Are Digital Isolators?

Digital isolators are used in a variety of applications to isolate digital signals by use of CMOS and similar components. Used in high-speed multichannel circuits, serial interfaces, and logic analyzer applications, digital isolators play an essential role in signal transduction. In this blog, we will discuss the basics of digital isolators while describing their importance in high-caliber circuitry.

In any large system containing grounding units, there is always the potential for a ground difference to occur, in which the ground of one part of the system uses a different voltage from another. This difference may cause damage to any connected devices due to intolerable voltage levels. Input sensors are commonly used to combat this phenomenon by altering the voltage level before the current reaches the output. Unfortunately, ground differences may also skew sensor data, thus decreasing their efficacy. By implementing a digital isolator, the input sensor can better perform its task in protecting the associated data and devices.

Digital isolators make use of modulators and receivers to couple data across a barrier. The modulator sends a high-frequency carrier across an isolation barrier, where it then meets a receiver that can filter the signal and yield an isolated output. They are composed of complementary metal-oxide-semiconductor (CMOS) or transistor-transistor logic (TTL) devices, both of which have voltage ranges from 0-5V.

The quality of a digital isolator is largely dependent on its structural design, insulation material, and data transfer method. Insulating materials such as polyimide and silicon dioxide that have long been used in optocouplers are generally chosen for digital isolators. These highly-effective materials typically provide device longevity well over the expected timeframe.

Digital isolators may employ either magnetic or capacitive methods to couple data. Magnetic coupling is performed by transformers, which create a localized magnetic field by applying a small current to a coil. This coupling method can work effectively at more considerable distances between the modulator and receiver. As such, isolators designed with transformers may be fitted with a thicker coat of insulation, thus providing less noise to the system. Conversely, capacitors require the modules to be closer together and have less capacity to reject transient noise signals. However, capacitors use a lower current compared to transformers, which becomes more important at higher data transfer rates.

Before digital isolators became widely used, optocouplers had long been the preferred method to transmit data across an isolation barrier. Comparatively, digital isolators use more sophisticated circuitry in order to handle complex system requirements. For example, transformers use a pulse protocol to create the magnetic field, which significantly reduces power consumption as compared to optocouplers, which have a continuous power requirement. However, other transmission methods such as RF modulation require a steady current.

Digital isolators may be used in a variety of circuity applications. One of the most common is to protect operators from transient high-voltage events, which would otherwise cause injury. Additionally, computer processors that are sensitive to voltage levels may benefit from isolation. Finally, many medical devices and electric vehicles contain varying ground voltages and require digital isolation.

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