Transistors and Amplifiers Overview

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Questions and Answers

What device is considered the most effective for weak-signal amplification?

Field-effect transistor (correct)

Vacuum tube and field-effect transistor both

Vacuum tube

Bipolar transistor

What is the specification that denotes the effectiveness of a weak-signal amplifier?

Sensitivity (correct)

Power output

Distortion

Efficiency

In power amplification, efficiency is defined as:

The number of microvolts of signal input that produce a certain ratio of signal output to noise output

The gain set by the user

The ratio of signal power output to total power input (correct)

The extent to which the output waveform is a faithful replication of the input waveform

Which device is most frequently used for power amplification?

Bipolar transistor Signup and view all the answers

What is power output measured in?

Watts or kilowatts Signup and view all the answers

In audio applications, how efficient are power amplifiers typically?

30-50% Signup and view all the answers

What is the main purpose of an amplifier?

To create a large output signal from a small input signal Signup and view all the answers

Why is the term 'linear electronics' considered a misnomer?

Because many circuits classified as linear are actually nonlinear in nature Signup and view all the answers

In what type of applications are weak-signal amplifiers commonly used?

In wireless receivers and audio devices Signup and view all the answers

What distinguishes weak-signal amplifiers from other types of amplifiers?

Their ability to handle very small input signals with minimal noise Signup and view all the answers

What is one of the very earliest applications of electronic devices mentioned in the text?

Amplification Signup and view all the answers

How do amplifiers contribute to signal processing in various industries?

By creating larger output signals from small input signals Signup and view all the answers

What is the formula to calculate decibel power gain GdB in decibels?

GdB = 10 log10 (Po/Pi) Signup and view all the answers

In decibel computation, what factor appears when dealing with power gain?

A factor of 10 Signup and view all the answers

When multiple stages are connected in cascade, what is used to determine the net voltage gain in absolute form?

Product of all the individual gains Signup and view all the answers

What does a negative decibel voltage gain indicate?

A reduction of signal level through the circuit Signup and view all the answers

Why is it more convenient to work with losses rather than gains for voltage divider networks?

To make positive gains negative Signup and view all the answers

What is the difference between a negative voltage gain and a negative linear gain?

Negative voltage gain indicates signal inversion, while negative linear gain indicates signal reduction. Signup and view all the answers

Study Notes

Amplifiers and Amplification

The most effective device for weak-signal amplification is the field-effect transistor.
Sensitivity is the specification that denotes the effectiveness of a weak-signal amplifier, defined as the number of microvolts of signal input that produce a certain ratio of signal output to noise output (usually 10 to 1).

Power Amplifiers

Power amplifiers are used in wireless transmitters, broadcast transmitters, and hi-fi audio equipment.
The most frequently-used device for power amplification is the bipolar transistor, but vacuum tubes are becoming increasingly popular, especially among musicians.
Power output is measured in watts or kilowatts, and efficiency is the ratio of signal power output to total power input (wattage demanded of the power supply or battery).
Efficiency is typically expressed as a percentage, ranging from 30 to 50 percent in audio applications and 50 to 70 percent in wireless communications and broadcasting transmitters.

Ideal Amplifier

An ideal amplifier will pass the input signal through to the output undistorted but enlarged (gain set by user), with no delay.
An ideal amplifier includes all signal-processing functions associated with such signals.

Linear Electronics

Linear electronics is a category that includes all signal-processing functions associated with electronic devices.
Amplification is one of the most important applications of linear electronics.
Nonlinear circuits are also classified under linear electronics.

Amplifier

An amplifier uses a small input signal to create a large output signal, while minimizing distortion of the waveform.
Amplifiers are used for both electrical and optical signals.

Weak-Signal Amplifiers

Weak-signal amplifiers are used primarily in wireless receivers, acoustic pickups, audio tape players, and compact disc players.
They are designed to deal with exceedingly small input signals, in some cases measuring only a few nanovolts (units of 10-9 volt).
Weak-signal amplifiers must generate minimal internal noise while increasing the signal voltage by a large factor.

Decibel Power Gain

The decibel power gain GdB in decibels is defined by: GdB = 10 log10G = 10 log10 (Po/Pi).
A factor of 10 appears in decibel computation involving power gain, and a factor of 20 appears when voltage and current gains are used.

Cascaded Amplifiers

When two or more stages are connected in cascade, decibel measures are particularly convenient to use in dealing with combinations.
The net decibel gain is the sum of the individual decibel gains for the different stages.

Decibel Voltage Gain and Loss

The net voltage gain is determined in absolute form as the product of all the individual gains.
A negative voltage gain should not be confused with negative linear gain.
Negative gain corresponds to the reduction of the signal level through the circuit, while negative linear gain corresponds to an inversion of the polarity.
Voltage gains and their equivalents can be represented in decibel form.

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Description

Explore the basics of transistors and amplifiers, including the field-effect transistor for weak-signal amplification and power amplifiers commonly used in wireless and broadcast transmitters. Learn about sensitivity and power amplification in different electronic devices.