ABSTRACT
So far, we have mostly considered passive elements (resistors, capacitors and inductors), which simply transmit currents and voltages. Amplifiers involve active devices – transistors. The amplifier is a central feature of all electronic circuits. Sometimes it may be hidden from view inside the circuit and may not be immediately apparent in the relation between input and output, but it is always there. Even in digital circuitry where the output voltage is often the same as at the input, the circuit amplifies current.
