Unit 11 Electronic amplifier

I Read and memorise the following words:

1. circuit – схема, ланцюг

2. device – пристрій

3. modulating – модуляція

4. supply – забезпечувати

5. imperfect – недовиконаний

6. gain – одержувати

II Read and translate the text:

The term amplifier as used in this article can mean either a circuit (or stage) using a single active device or a complete system such as a packaged audio hi-fi amplifier.

An electronic amplifier is a device for increasing the power of a signal. It does this by taking power from a power supply and controlling the output to match the input signal shape but with a larger amplitude. In this sense, an amplifier may be considered as modulating the output of the power supply. Real world amplifiers are not ideal and this control is thus imperfect.

• One consequence is that the power supply itself may influence the output, and must itself be considered when designing the amplifier

• The amplifier circuit has an "open loop" performance, that can be described by various parameters (gain, slew rate, output impedance, distortion, bandwidth, signal to noise ratio ...)

• Many modern amplifiers use negative feedback techniques to hold the gain at the desired value.

Classification of amplifier stages and systems

Different designs of amplifiers are used for different types of applications and signals. We can broadly divide amplifiers into four categories:

• Small-signal amplifiers

• Low-frequency power amplifiers

• Radio-frequency (RF) power amplifiers

• Microwave power amplifiers

Each of these calls for a slightly different design approach, mainly because of the physical limitations of the components used to implement the amplifier, and the efficiencies that can be realised.

There are many alternative classifications that address different aspects of amplifier designs, and they all have some effect on the design parameters and objectives of the circuit. Amplifier design is always a compromise of numerous factors, such as cost, amount of power consumed, devices that have real-world imperfections, and the need to match the amplifier to the input signal as well as the output load.

Classification of amplifier stages by common terminal

One set of classifications for amplifiers is based on which device terminal is common to both the input and the output circuit. In the case of bipolar junction transistors, the three classes are common emitter, common base, and common collector. For field-effect transistors, the corresponding configurations are common source, common gate, and common drain; for triode vacuum devices, common cathode, common grid, and common plate.

Inverting or non-inverting

Another way to classify amps is the phase relationship of the input signal to the output signal. An inverting amplifier produces an output 180 degrees out of phase with the input signal (that is. an inversion or mirror image of the input as seen on an oscilloscope). A non-inverting amplifier maintains the phase of the input signal waveforms. An emitter follower is a type of non-inverting amplifier, indicating that the signal at the emitter of a transistor is following (that is. matching with unity gain but perhaps an offset) the input signal.

This description can apply to a single stage of an amplifier, or to a complete amplifier system.