Measuring inductance is a complex task. Methods proposed elsewhere require precise measurements with an oscilloscope in its usual (voltage vs. time) display mode. Methods based on building a filter with the inductor and finding the cutoff or natural frequency assume a sufficiently high-Q that peak/null detection is obvious. In practice, I find these methods hard to apply.
Is there an easier method to measure inductance using a hobby-grade oscilloscope?
Continue reading Measuring Inductance
Input signals often have a DC component that is not of interest and inconvenient to work with. The DC component might be unknown or of a value that doesn’t match the circuit the input is driving. Under standard linear circuit assumptions, the response to the time-varying component of the input is independent of the DC component, so we can strip away the DC component and replace it with a more convenient value. A blocking capacitor generally provides the “AC Coupling” of the input signal.
A problem with blocking capacitors arises when I try to select one for my audio circuits. To the signal source, my circuit appears to have some input impedance, R, and the equivalent circuit becomes a single-pole high-pass filter:
The commonly-defined “cut-off” frequency for such a circuit is , and I often try to have a cut-off frequency one decade below my lowest frequency of interest. To accomplish this I need a very large RC product, but the input impedance of my circuit is generally too low. Continue reading AC Coupling using an Emitter Follower