In Practice

摘要

Q: In the October 2009 column you said, "Supply rail decoupling can be a tricky subject." Can you expand on that? A: Figure 1 recalls Figure 1 from the October article, and shows a transistor AF amplifier that develops its output voltage across the collector load resistor R1. An essential feature of this circuit is the decoupling capacitor C1, connected between the DC supply end of the load (point D) and this stage's local 'ground' point G. In RF circuits the collector load would usually be a tuned circuit or some kind of RF transformer and, of course, the active device could also be a FET or a valve; but in every case, the circuit needs a decoupling capacitor from D to G.