ANALOG

ELECTRONICS
BY
RWENDEIRE ANDREW
ELECTRICAL ENGINEER (POWER)
B.ENG.ELECTRICAL. MSC. POWER SYSTEMS ENG.
+256788993858 / +256782151445
andrewrwe@gmail.com / andrewrwend@gmail.com
 POWER AMPLIFIERS
• Audio and RF power amplifiers; Class A, B, AB, C, D, E and F.

• IC Power Amplifiers. Design considerations and applications;

• Bipolar and FET Differential Amplifiers: DC and AC analysis.

• Single and Double ended operation.

• Differential gain, common mode gain common mode rejection ratio.

 INTRODUCTION
• An amplifier receives a signal from some pickup transducer or other input source and provides a
larger version of the signal to some output device or to another amplifier stage.

• Consider a transducer signal; these are generally small signals, a few millivolts from a cassette, this
signal needs to be amplified to sufficiently operate an output device like a speaker.

• In small signal amplifiers, the main factors are usually amplification linearity and magnitude of
gain. Since signal voltage and current are small in a small-signal amplifier, the amount of power-
handling capacity and power efficiency are of little concern.

• A voltage amplifier provides voltage amplification primarily to increase the voltage of the input
signal.
 INTRODUCTION…
• Large-signal or power amplifiers, on the other hand, primarily provide sufficient power to an
output load to drive a speaker or other power device, typically a few watts to tens of watts.

• These amplifier circuits handle large-voltage signals at moderate to high current levels.

• The main features of a large-signal amplifier are the circuit’s power efficiency, the maximum
amount of power that the circuit is capable of handling, and the impedance matching to the output
device.

• One method used to categorize amplifiers is by class.

• Amplifier classes represent the amount the output signal varies over one cycle of operation for a
full cycle of input signal.
 AMPLIFIER EFFICIENCY

• In order to deliver sufficient current to the load, power

amplifiers must have a very low value of output impedance

• PENT power surrendered by the power supply

• PEXC excitatory power (worthless magnitude)

• PSAL output power on the useful load

• PDIS power dissipated by the amplifier (their exit

component/s)
 AMPLIFIER GAIN
• The amount of amplification or gain is an important parameters of an amplifier
• Gain is simply the ratio of output voltage to input voltage, output current to input current, or output
power to input power

• Thus
 EXAMPLE
An amplifier produces an output voltage of 2 V for an input of 50 mV. If the input and output
currents in this condition are, respectively, 4 mA and 200 mA, determine:

(a) the voltage gain; (40)

(b) the current gain; (50)

(c) the power gain. (2000)

 AMPLIFIER CLASSES OF OPERATION
• linear amplifiers: the output signal should be a faithful copy of the input signal although somewhat
larger in amplitude.

• non-linear amplifiers: the input and output waveforms will not necessarily be similar.

• The degree of linearity provided by an amplifier can be affected by a number of factors including
the amount of bias applied, and the amplitude of the input signal

• a linear amplifier will become non-linear when the applied input signal exceeds a threshold value.
Beyond this value the amplifier is said to be overdriven
 CLASS A AMPLIFIER
• Active device(s) must be operated in the linear part of their
transfer characteristic

• For class A, the input and output signals for an amplifier are
operating in linear mode.

• The bias point is adjusted to the mid-point of the linear part of

the transfer characteristic.

• Current will flow in the active devices used in a Class A

amplifier during a complete cycle of the signal waveform. At no
time does the current fall to zero.
 CLASS A AMPLIFIER…
• When the bias point is moved down the
transfer characteristic and, at the same
time, increasing the amplitude of the input
signal

• The signal is distorted.

• This effect arises from the nonlinearity of

the transfer characteristic that occurs near
the origin (i.e. the zero point)
 CLASS AB AMPLIFIER
• Now consider the case of reducing the bias even further
while further increasing the amplitude of the input signal

• The bias point has been set at the projected cut-off point.

• The negative portion of the output signal becomes cut off (or
clipped) and the active device(s) will cease to conduct

•
 CLASS B AMPLIFIER
• No bias at all is applied to the amplifier

• The output signal will only comprise a series of positive

half-cycles and the active device(s) will only be conducting
during half-cycles of the waveform (50% of the time).

• This mode of operation (Class B) is commonly used in high-

efficiency push-pull power amplifiers where the two active
devices in the output stage operate on alternate half-cycles
of the waveform
 CLASS C AMPLIFIER
• The bias point is set at beyond the cut-off (zero) point and a
very large input signal is applied.

• The output waveform will then comprise a series of quite

sharp positive-going pulses. These pulses of current or
voltage can be applied to a tuned circuit load in order to
recreate a sinusoidal signal.

• The pulses will excite the tuned circuit and its inherent
flywheel action will produce a sinusoidal output waveform.
This mode of operation is only used in RF power amplifiers
that must operate at very high levels of efficiency.
 CLASS D AMPLIFIER
• This operating class is a form of amplifier operation using pulse (digital) signals, which are on for
a short interval and off for a longer interval.

• Using digital techniques makes it possible to obtain a signal that varies over the full cycle (using
sample-and-hold circuitry) to recreate the output from many pieces of input signal.

• The major advantage of class D operation is that the amplifier is on (using power) only for short
intervals and the overall efficiency can practically be very high.
SUMMARY
 INPUT AND OUTPUT RESISTANCE
• Input resistance is the ratio of input voltage to input current and it is expressed in ohms.
• The input of an amplifier is normally purely resistive (i.e. any reactive component is negligible) in
the middle of its working frequency range (i.e. the mid-band).
• In some cases, the reactance of the input may become appreciable (e.g. if a large value of stray
capacitance appears in parallel with the input resistance). In such cases we would refer to input
impedance rather than input resistance.
• Output resistance is the ratio of open-circuit output voltage to short-circuit output current and is
measured in ohms. This resistance is internal to the amplifier and should not be confused with the
resistance of a load connected externally.
• As with input resistance, the output of an amplifier is normally purely resistive and we can safely
ignore any reactive component. If this is not the case, we would once again need to refer to output
impedance rather than output resistance
INPUT AND OUTPUT RESISTANCE…
 TRANSISTOR AMPLIFIERS
• The transistor circuit configurations depend upon which one of the three transistor connections is
made common to both the input and the output.
• These configurations are: common emitter, common collector (or emitter follower) and
common base.
 COMMON BASE, EMITTER, COLLECTOR
CIRCUITS
• RECALL:
 APPROXIMATE COMMON BASE, EMITTER
CONFIGURATION.
• β is temperature sensitive, especially for silicon transistors.
• The term biasing appearing in the title of this chapter is an all-inclusive term for the application of dc voltages
to establish a fixed level of current and voltage.
 SERIES-FED CLASS A AMPLIFIER
• Not the best to use as a large-signal amplifier
because of its poor power efficiency.
• The beta of a power transistor is generally less than
100,
• The overall amplifier circuit using power transistors
that are capable of handling large power or current
while not providing much voltage gain.
• The factor β (beta) of a BJT is an amplification
factor
• RECALL:
SERIES-FED CLASS A AMPLIFIER
 COLLECTOR CHARACTERISTIC
• The AC load line is drawn using the values of Vcc and Rc.
• The intersection of the dc bias value of IB with the dc load
line then determines the operating point (Q-point) for the
circuit.
• If the dc bias collector current is set at one-half the possible
signal swing (between 0 and Vcc/Rc), the largest collector
current swing will be possible.
• Additionally, if the quiescent collector-emitter voltage is set at
one-half the supply voltage, the largest voltage swing will be
possible.
IN PUT OF SERIES FED CLASS A AMPLIFIER
• When an input ac signal is applied to the amplifier the output will vary from its dc
bias operating voltage and current. A small input signal will cause the base current
to vary above and below the dc bias point, which will then cause the collector
current (output) to vary from the dc bias point set as well as the collector-emitter
voltage to vary around its dc bias value.

• As the input signal is made larger, the output will vary further around the
established dc bias point until either the current or the voltage reaches a limiting
condition. For the current, this limiting condition is either zero current at the low
end or Vcc/Rc at the high end of its swing. For the collector-emitter voltage, the
limit is either 0 V or the supply voltage, Vcc.
OUT PUT OF SERIES FED CLASS A AMPLIFIER
• The output voltage and current varying around the bias point provide ac
power to the load. This ac power is delivered to the load, RC, in the
circuit. The ac signal, Vi, causes the base current to vary around the dc
bias current and the collector current around its quiescent level, ICQ.

• The ac input signal results in ac current and ac voltage signals. The

larger the input signal, the larger the output swing, up to the maximum set
by the circuit. The ac power delivered to the load (RC) can be expressed
in a number of ways
 POWER CONSIDERATIONS OF SERIES FED
CLASS A AMPLIFIER
• The power into an amplifier is provided by the supply. With no input signal, the dc current drawn is
the collector bias current, ICQ. The power then drawn from the supply is

• Even with an AC signal applied, the average current drawn from the supply remains the same, so
that the above equation represents the input power supplied to the series fed class A amplifier.
 MAXIMUM EFFICIENCY OF SERIES FED CLASS
A AMPLIFIER.
• For the series fed class A amplifier., the maximum efficiency can be determined using the
maximum voltage and current swings. For the voltage swing, it is
 MAXIMUM EFFICIENCY OF SERIES FED CLASS
A AMPLIFIER…
• The maximum efficiency of a series fed class A amplifier is thus seen to be 25%. Since this
maximum efficiency will occur only for ideal conditions of both voltage swing and current swing,
most series fed circuits will provide efficiencies of much less than 25%
• The amplifier is an electronic device used to increase the signal
of current, voltage and power.
• The amplifier is quite opposite to an attenuator if the amplifier
provides the gain, hence the attenuator provides the loss
 CLASS A AMPLIFIER
• To obtain high linearity and gain in class A amplifier the output of the class A amplifier should be biased
ON for all times.

• Class A amplifier is biased so that it conducts over the whole of the cycle of the waveform. It conducts
all of the time, even for very small signals, or when no signal is present

• The Class A amplifier is inherently the most linear form of amplifier.

• As the output device is always conducting this current represents a loss of power in the amplifier. In fact
the maximum theoretical efficiency that a class A amp can achieve is 50% efficiency with inductive
output coupling or just 25% with capacitive coupling.

• The Class A amplifier provides a linear output with the lowest distortion, but it also has the lowest
efficiency level.
 CLASS A AMPLIFIER…
Advantages

• It eliminates Non-linear distortion

• It has low ripple voltage

• It does not require any frequency compensation

• There is no cross and switching distortions

• There is low harmonic distortion in the voltage and current amplifier

Disadvantages

• The transformers used in this amplifier are bulk and they are high cost

• Its requirement of two identical transistors

• Low efficiency
 CLASS B AMPLIFIER
• A class B amplifier is biassed so that it conducts over half the waveform by using two amplifiers,
each conducting our half the waveform, the complete signal can be covered.
• Class B amplifiers called “push-pull,” because the outputs of the active devices have a 180° phase
relationship.
• The efficiency is much higher, but the class B amplifier suffers from what is termed cross-over
distortion, where one half of the amplifier turns off and the other comes into play. This results
from non-linearities which occur close to the changeover point where one device is turning on and
the other is turning off. This point is notoriously non-linear, and the distortion is particularly
noticeable for low level signals where the non-linear section of the curve represents a much larger
portion of the overall signal.
• Although the maximum theoretical efficiency of a class B amplifier is 78.5%, typical efficiency
levels are much lower.
 CLASS B AMPLIFIER…
• Uses two amplifiers, each conducting one half the waveform,
the complete signal can be covered
• Two active devices are used and input waveform is split so that
one active device conducts during half of an input cycle, the
other during the other half.
• The two halves are summed at the amplifier output to
reconstruct the complete waveform.
• if the input signal is positive, then the positively biased
transistor conduct and the negative transistor is switched OFF. If
the input signal is negative, then the positive transistor switches
OFF and negative biased transistor turn ON. Hence the
transistor conduct half of the time whatever it may be like
positive or negative half cycle of the input signal
 CLASS B AMPLIFIER…
Advantages
• Some amount of distortion in the circuit gives the more output per device because of there is no
presence of the even harmonics
• The use of push-pull system in the class B amplifier eliminates the even harmonic
Disadvantages
• In the class B amplifier, there is high harmonic distortion
• In this amplifier, there is no need for self bias
Applications
• The class B amplifiers are used in low-cost design
• This amplifier is more significant than the class A amplifier
• The class B amplifier suffers from the bad distortion if the signal level is low
 CLASS AB AMPLIFIER…
• The class AB is the combination of class A and class B amplifier. The class AB amplifiers are using
commonly in the audio power amplifiers. From the diagram the two transistors have the small
amount of voltage which is 5 to 10% of the quiescent current and the bias the transistor just above
the cutoff point.

• In the class AB amplifier design each of the push-pull transistors is conducting slightly more than
the half cycle of conduction in class B, but much less than the full cycle of conduction of class A.
 CLASS AB AMPLIFIER…
• Class AB amplifier falls between Class A and Class B.

• It seeks to overcome the cross-over distortion by slightly

turning on the transistors so that they conduct for slightly
more than half the cycle and the two devices overlap by a
small amount during the switch-on / switch-off phase,
thereby overcoming the crossover distortion.

• This approach means that the amplifier sacrifices a certain

amount of potential efficiency for better linearity - there is
a much smoother transition at the crossover point of the
output signal.
 CLASS AB AMPLIFIER…
Advantages

• The class AB has a linear behavior

• The design of this amplifier is very simple

• The distortion of this amplifier is less than 0.1%

• The sound quality of this sound is very high

Disadvantages

• The power dissipation of this amplifier generates the heat and requires large amount of heat sink

• This amplifier has low power efficiency and the average efficiency is less than the 50%
 CLASS C AMPLIFIER
• Class C amplifiers are biassed so that they conduct over much less than half a cycle.
• Class C amplifiers have very high levels of distortion, but also it enables very high efficiency
levels to be achieved.
• This type of amplifier can be used for RF amplifiers that carry a signal with no amplitude
modulation - it can be used for frequency modulation with no issues.
• The harmonics created by the amplifier effectively running in saturation can be removed by filters
on the output.
• These amplifiers are not used for audio applications in view of the level of distortion.
• Efficiency levels can be as high as 80% but values of 66% are normal if losses are taken into
account
 CLASS C AMPLIFIER…
• The class C amplifier is a deeply biased hence the output current is zero
for more than the one-half of the input signal and the transistor idling at
the cut off point.

• Class C amplifiers typically use a single active device that is biased well
into its off region. As the signal is applied, the top peaks of the signal
cause the device to run into conduction, but obviously for only a small
portion of each input-waveform cycle.

• At the output the circuit uses a high-Q, L-C resonant circuit. This circuit
effective rings after it is hit by each pulse so that the output contains an
approximation to a sine wave. Filtering is required on the output to
ensure that the level of harmonic is sufficiently low.
 CLASS C AMPLIFIER…
Advantages
• The efficiency of Class C amplifier is high
• In class C amplifier the physical size is low for the given o/p power
Disadvantages
• The linearity of Class C amplifier is low
• The class C amplifiers are not used in the audio amplifiers
• The dynamic range of the class c amplifier is decreased
• The class C amplifier will produce more RF interfaces
Applications
• This amplifier is used in the RF amplifiers
 CLASS D AMPLIFIER
• The class D amplifier is non-linear switching amplifiers or PWM amplifiers. This amplifier can
reach 100% efficiency in theoretically and there is no period during the cycle. The voltage and the
current waveforms overlap current is drawn only with the help of transistor which is in ON state.
These amplifiers are also called as the digital amplifiers

• In reality the actual levels attained are less, but nevertheless the efficiency levels achieved are very
much higher than the other analogue classes.
Advantages
• The class D amplifier has more efficiency that is more than 90%
• In the class D amplifiers, there is a low power dissipation
 CLASS D AMPLIFIER…
Disadvantages

• The design of the class D amplifier is more complex

than the class AB amplifier.

Applications

• This amplifier is used in the sound cards of the mobile

devices and personal computers

• These amplifiers are used in cars of audio subwoofer

amplifiers.

• Nowadays, in most of the applications, these

amplifiers are using.
 CLASS F AMPLIFIER
• The F amplifiers are used to increase the efficiency and
output by the harmonic resonators in the form of output
network and to shape the output waveform in a square wave.

• The class F amplifiers have more than 90% of efficiency if

the infinite harmonic tuning is used.
 CLASS S AMPLIFIER
• The class S amplifiers are similar operations to the class D
amplifiers.

• These amplifiers are Non-linear switching mode amplifiers.

• It converts the analog input signals to the digital square

wave pulses by using the delta-sigma modulations. It
amplifies them to increase the output power by the help of
band pass filter.

• The digital signal of the switching amplifier is fully in ON

or OFF state and its efficiency can reach 100%.
 CLASS T AMPLIFIER
• The class T amplifiers are designed with a type of digital
switching amplifiers.
• These amplifiers became more popular as an audio
amplifier design because of the extension of the DSP
chip and multi-channel sound amplifier.
• This amplifier converts the signal from analog signal to
the digital pulse width modulation signal and the
amplification increase the efficiency of an amplifiers.
• The class T amplifiers are the combination of low
distortion signal of class AB amplifier and the other one
is the efficiency of class D amplifier.
 CLASS G AMPLIFIER
• The enhancement of class G Amplifier is the basic of
Class AB Amplifier. The class G amplifier used in the
multiple power supply rails of different voltages.

• Automatically switches between the supply rails as the

input signal changes.

• The contact switching decreases the average power

consumption hence, the power loss is produced by the
wasted heat.
 CLASS G AMPLIFIER…
• Class G is a form of amplifier that uses multiple power supplies rather than just a single supply.

• For low level signals a low voltage supply is used, but as the signal level increases, so a high voltage supply is
utilised.

• This gives a very efficient design as additional power is only used when it is actually required.

• The change both the higher voltage supply can be achieved without detriment to the output signal fidelity.

• The amplifier is able to provide both low levels of distortion, whilst also providing high levels of efficiency.

• This approach can be complex to design from scratch, but if engineered correctly, it can work well. Fortunately the
difficulty of design can be reduced if one of the many audio ICs that use Class G is used.