These two dies are separated by a physical gap containing a transparent insulating shield intended to reduce parasitic input/output coupling capacitance. The optocoupler’s hybrid construction attaches the LED and output die to a split lead frame. An X-Ray view of a single-channel optocoupler is shown in Figure 2a. While the basic operating principles of both the CMOS digital isolator and optocoupler are similar, the physical implementation of each is quite different. The receiver, therefore, detects no in-band carrier energy and drives VOUT low. When VIN is low, the transmitter is disabled, and no carrier is present.
The receiver asserts logic 1 on VOUT when sufficient in-band carrier energy is detected. When VIN is high, the transmitter generates an RF carrier that propagates across the isolation barrier to the receiver. Data is transferred from input to output using simple on/off keying (OOK). The CMOS digital isolator consists of two identical semiconductor dies connected together within a standard IC package forming an RF transmitter and receiver separated by a differential capacitive isolation barrier. The basic operation of the CMOS digital isolator is analogous to that of the optocoupler, except that an RF carrier is used instead of light (Figure 1b). When LED forward current no longer flows, light emission ceases, and the output transistor turns off.įigure 1. Emitted light passes through an optically transparent insulating film (or dielectric), striking a photo detector and causing a current flow that biases the output transistor on. As shown in Figure 1a, the optocoupler is a hybrid assembly having a light-emitting diode (LED) that emits light when forward biased, with brightness being proportional to LED forward current. This white paper discusses industrial isolation issues and ways RF isolation technology can be applied to increase system robustness and performance.įigure 1 shows top-level block diagrams of an optocoupler and the CMOS digital isolator. Of the competing silicon isolators currently on the market, the Silicon Labs CMOS digital isolator family is the most advanced, offering best-in-class timing performance, electromagnetic interference (EMI) and external field immunity, power consumption, size, and cost. Over the last four decades, optocouplers have been the “default” signal isolation device, but recent breakthroughs in silicon isolation technology have spawned smaller, faster, and more reliable and cost-effective solutions that have already begun supplanting optocouplers in many end applications. This environment presents challenges for designing reliable isolation circuits that deliver error-free operation over long equipment lifetimes. It is well known that industrial equipment must operate reliably in the harshest environments, where strong electromagnetic fields, surges, fast transients, and high noise floors are the norm. Industrial electronic equipment commonly uses galvanic isolators to protect systems and users from potentially hazardous voltages. Isolation circuits designed to withstand the rigors of industrial environments are the focus of this white paper. CMOS Digital Isolators Supersede Optocouplers in Industrial Applications
0 kommentar(er)
