It is an R L circuit or filter. It is driven by an output resistance R.
Every source of voltage, AC or DC has a non 0Ω output impedance. Effectively Rout is a series resistance. According to Ohm's law when we draw current the voltage drops at this resistance. A potential devider.
Connecting an L in parallel is the opposite of connecting a capacitor C in parallel which reduces the high frequency content.
The impedance of C decreases as frequency rises. So it becomes increasingly towards being a short circuit. So the output voltage of the source is forced to drop.
The opposite with an L. As frequency increases its impedance increases. So the source is less and less loaded and there is treble increase.
See also L Pleiades microphone filters and gentler slope (R,L) Pleiades filters connected in parallel with mic output.
Other example is driving a magnetic tape recording head. It is an inductor. So if it is driven by a high output impedance which is the case, the voltage across it increases as frequency rises.
Other example is an output transformer if it has a low inductance compared to the output impedance of what drives it.
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