Protecting the differential input stage from damage is accomplished by limiting the voltage across the base-emitter junctions. This protects the amplifier, as ESD currents are routed to the power supplies and bypass capacitors, rather than through the sensitive active circuitry.Ībrupt voltage changes across an op amp’s input can reverse bias the input differential pair, leading to latent defects, increased input bias current, and increased offset voltage. These on-chip diodes are connected from the op amp inputs and outputs to the power supply rails. ESD diodes protect the amplifier against static electricity, electrostatic induction, and other ESD events. Common-mode over-voltage protection primarily limits the input voltage to be compatible with the safe operating range of the amplifier. Various forms of input protection can be found in high-speed amplifiers: common-mode over-voltage protection, electrostatic discharge (ESD) protection, and input differential pair protection are some of the common ones. It also presents alternatives and circuit solutions that utilize amplifiers with input protection. This article discusses the need for input protection, its implementation, and its potential drawbacks. In most cases, this protection is transparent to the user, but in some applications it can be the circuit’s Achilles’ heel. Many of today’s high-speed op amps have on-chip input protection.
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