TABLE OF CONTENTS Marc Thompson
| Note | 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 |
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]
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...
