From fly-by-wire aircraft to cardiac monitoring devices to the safety-critical components of an electric vehicle, humans are increasingly placing trust for our safety in the electronic systems surrounding us. For these systems to protect us, all have one thing in common – the need for clean power. To ensure reliable power to these systems, designers must use bypass capacitors.

Why are Bypass Capacitors Necessary?

Most electronic designs are complex and compact, resulting in many opportunities for introducing noise into the system. Even with careful layout considerations, any DC power line can act as an inductor that absorbs and transmits electromagnetic fields from high-speed digital sources such as DDR RAM data lines or AC power lines. The quality of the power provided is reduced when these emissions are loaded on top of the desired steady-state DC voltage. In addition, transient voltage spikes from electrostatic discharge (ESD), lightning, or other sources of electromagnetic interference (EMI) can seriously damage mission-critical integrated circuit (IC) components. 

Some potential EMI-induced failure modes range from single-bit flips and glitches that robust hardware and software solutions are designed to correct to IC latch-up, forcing a system reset. Large ESD spikes may cause total IC failure. 

To ensure that expensive, high-speed components are provided with clean power consistently, designers add bypass capacitors as close to the IC power input leads as possible. The bypass capacitor acts as a filter,  providing infinite resistance to steady-state voltage, adding stored charge back on the line in case of voltage reductions, or bypassing to ground voltages exceeding the steady-state equilibrium. (See Figure 1.)

Capacitors are typically manufactured in the following forms:

• Ceramic capacitors with metal electrodes and ceramic dielectric 
• Electrolytic capacitors with aluminum or tantalum electrodes and liquid or solid electrolyte dielectric
• Film capacitors with metal electrodes deposited on both sides of a plastic film dielectric
• Tantalum capacitors with tantalum as the electrodes and tantalum pentoxide as the dielectric material.

Bypass capacitors commonly use ceramic capacitors as they can be manufactured with a layered dielectric material and surface mount topologies that reduce equivalent series inductance (ESL) and equivalent series resistance (ESR) while bypassing high-frequency EMI. Ceramic capacitors can also operate in a wide range of temperatures.

Although this discussion emphasizes microprocessor or DSP IC applications, the ability of bypass capacitors to provide clean power encompasses all IC jobs. For example, a Magnetic Resonance Imaging (MRI) scanning device employs bypass capacitors in its power supplies, its RF Pulse Generators, which send radio pulses to excite cells in the body to emit photons, its signal reception circuits that capture the resulting excited photons, and amplifiers to increase the strength of the incoming weak signals received. Bypass capacitors employed in the image display systems ensure sharp results are presented to clinicians. MRI imaging has dramatically revolutionized the diagnosis of human illnesses and resulted in life-saving treatment plans. Their design relies on bypass capacitors to ensure every phase of the imaging sequence provides the highest quality results.

Providing Solutions that Meet Regulatory Requirements.

Since we place our safety in the hands of engineers designing systems that defend and drive our world, the systems must meet the highest standards available. World regulatory bodies have agreed to a standard of electromagnetic compatibility (EMC), which means devices will not emit or receive electromagnetic energy causing EMI. 

Various regulatory bodies provide design guidelines to meet their functionality and human safety requirements. The U.S. Department of Defense MIL-Specs outlines criteria for systems to protect and defend our country reliably. Following the Food and Drug Administration, Title 21 CFR Part 820 – Quality System Regulation (QSR) (pdf) ensures medical devices protect human lives. The Federal Communications Commission Title 47 CFR Part 15 and Part 18 cover safety aspects of radio frequency devices and industrial, scientific, and medical equipment. 

Every electronic device that impacts our lives requires due diligence in design to ensure that guidelines are met or exceeded. Bypass capacitors are a critical component in ensuring the safety and efficacy of all electronic equipment.

If you are interested in publishing this or similar content to your blog, feel free to contact me.