Ch 3Transistor Amplifiers — 2nd PUC Electronics, concept-first.

Nearly every electronic device — a radio, a mobile phone, a public-address system, a music system — depends on making a weak electrical signal stronger.

An amplifier is a device that receives a small electrical signal and enlarges it; the process of increasing the strength of a weak electrical signal is called amplification.

BJT amplifiers are built in one of three configurations — CB, CC or CE — chosen for a particular application on the basis of their characteristic parameters.

When only one transistor with its associated circuitry is used to amplify a weak signal, the circuit is called a single-stage transistor amplifier.

In a working transistor amplifier, direct current from the biasing supply and alternating current from the signal being amplified flow through the same components at the same time.

A small-signal amplifier is essentially a voltage amplifier — it turns a small input voltage into a much larger output voltage but can deliver very little power.

Very often the voltage gain, power amplification or frequency response available from a single stage of amplification is not enough to drive the load or to build up a strong enough signal.

Amplifier configurations. A transistor amplifier can be built in common-emitter (CE), common-base (CB) or common-collector (CC) configuration.