From Analog Circuits: World Class Designs

Marc Thompson


Here, Marc explains why a resistance and a capacitance are not trivial items. Real resistors and real capacitors have several reactive or lossy components. Is this part of our circuit design work? Yeah. So we have to engineer to get the system working despite component imperfections. Sometimes wise component choice is a very important part of our job./rap

In This Chapter

Here we consider some of the subtleties of passive components, including construction techniques of these devices and parasitic effects. We'll cover some details about resistors, capacitors, and inductors. Then we'll use what we've learned in an illustrative discussion of PC board layout issues.


At first blush, a resistor is a resistor is a resistor. However, we'll now delve into some of the subtleties of these devices. The impedance of an ideal resistor is not dependent on operating frequency, [1] and is:

A real-world resistor ( Figure 5-1) includes a parasitic inductance, due to the geometry of the lead length, and a parasitic capacitance across the resistor. The impedance of the resistor, including these parasitic elements, is: [2]

Figure 5-1: Resistor R showing parasitic elements series inductance L p and parallel capacitance C p.

We can put this in " j ?" form by making the substitution s = j ?, resulting in:

For a large-valued resistor, [3] the RC time constant dominates. This is because a large resistor will swamp out the value of the parasitic...

Products & Services
Resistors are electrical components that oppose the flow of either direct or alternating current. They are used to protect, operate, or control circuits.
Chip Resistors
Chip resistors are passive resistors with a form factor of an integrated circuit (IC) chip. Typically, they are manufactured using thin-film technology.
Current Sensing Resistors
Current sensing resistors convert the current flowing through it to a voltage drop. Monitoring or measuring this voltage drop allows the current through the resistor to be measured. Applications for current sensing resistors include power supplies, receptacles, and battery packs. 
RF Inductors
RF inductors are special inductors designed to be used in radio frequency (RF) and microwave applications.
Power Resistors
Power resistors are used in power generation and distribution, high-voltage applications, control systems, and other power system applications. They include load banks, grounding resistors, and dynamic braking resistors.

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