laptop audio amplifier

LAPTOP AUDIO AMPLIFIER

1.1 INTRODUCTION:

All Laptops with Integrated Audio have built in speakers.

However the sound quality and available volume of built in speakers is often inadequate for

high quality music play back, MDI work, multimedia applications, or business presentations

before a large group. In these cases, you will want to attach more powerful and higher quality

speakers to your laptop`s speaker jack.

If your laptop has S/PDIF digital output, you will need to connect your laptop to a home

theatre system with an S/PDF input to be able to play back digital audio from sources such as

DVD movies. In either case, you should try to select the highest quality speakers you can

afford.

When you need to add external speakers, look for the best performance available in a small

space. I recommend small bookshelf speakers instead of standard stereo speakers, especially

if you must travel with speakers.

You should not depend on the onboard audio system in your notebook to provide adequate

amplification. Instead, use self-powered, magnetically shielded speakers. Magnetic shielding

is especially important if you are using a CRT monitor along with your laptop in a business

Administration.

With dozens of brands and models on the market at a variety of price points, it`s essential to

stand how to evaluate the quality of any given speaker. Speakers are measured by three

criteria:

FREQUENCY RESPONSE: A measurement of the range of high and low sounds a

speaker can reproduce. The ideal range is 20Hz-20KHz, the range of human hearing. No

speaker system reproduces this range perfectly. In fact, few people hear sounds 18KHz. An

exceptional speaker might cover over a range of 30KHz-23,000Hz, and lesser models might

cover only 100Hz-20,000Hz. Frequency response is the most deceptive specification because

identically rated speakers can sound completely different.

1

DEPT. OF ECE, ABHINAV HI-TECH COLLEGE OF ENGINEERING


TOTAL HARMONIC DISTORTION:

An expression of the amount of distortion or noise

created by amplifying the signal. Simply put, distortion is the difference between the sound

sent to the speaker and the sound you hear. The amount of Distortion is measured in

percentages. An acceptable level of distortion is less than 0.1%. For some CD-quality

recording equipment, a common standard is 0.05%, but some speakers have a distortion of

10% or more. Headphones often have a distortion of about 2% or more.

WATTS:

Usually stated as watts per channel, this is the amount of amplification available to

drive the speakers. Check that the company means “per channel” (or RMS) and not the total

power. Many audio adapters have built-in amplifiers, providing up to 8 watts per channel

(most provide 4 watts). This wattage is not enough to provide rich sound, however, which is

why many speakers have built-in amplifiers. With the flick of a switch or the press of a

button, these speakers amplify the signals they receive from the audio adapter. If you do not

want to amplify the sound, you typically leave the speaker switch set to “direct.” In most

cases, you`ll want to amplify the signal.

To overcome all these drawbacks an Audio amplifier specialized only for Laptops have been

to enhance the sound outcome and also the quality of sound.

2



2.1 BLOCK DIAGRAM OF LAPTOP AUDIO AMPLIFIER:

2.1.1 Block Diagram of Laptop Audio Amplifier

DESCRIPTION OF VARIOUS BULDING BLOCKS:

INPUT SECTION:

We refer the input section as laptop and stereo interfacing where in

the laptop is connected to stereo through 3.5mm jack cable. The audio signal through stereo

is taken as input, it is connected to amplifier circuitry through audio jack cable.

IC AMPLIFIER SECTION:

It is the main part of the experimental setup. We prefer to

use a IC amplifier rather than a transistor amplifier keeping in the advantage less complexity

and voltage gain of an IC amplifier when compared with transistor amplifiers. To serve this

purpose we use here IC LA 4440 so as to minimize the external circuitry other than the

amplifier section.


LAPTOP AND

STEREO INTERFACI

NG

IC AMPLIFER SECTION

NOISE FILTERS

INPUT SECTION

OUTPUT UNIT


3

NOISE FILTERS:

The external component connected to IC LA 4440 solve the noise

disturbances, hence we refer them as noise filter section.

OUTPUT UNIT:

The loud speakers which can enhance the audibility of sound output

form amplifier section are connected as load. This is termed as output unit.

4



3.1 IC AMPLIFIERS:

There was a time when the use of ICs (Integrated Circuits) in

high-end audio was almost universally regarded as undesirable. The first ICs designed in the

1960's and 70's had poor slew rates and a host of other problems, making them inferior to

discrete designs. However, times have changed. Over 40 years of collective design

experiences have transformed the scene. We now understand more about various

mechanisms of distortion and have the advantage of more advanced fabrication technologies

and faster transistors. IC power amplifiers built using National Semiconductor's

LM3886/LM4780 offer truly exceptional performance, on a par with or even superior to

discrete designs.

Its sonic potential was first noted by 47 Laboratories, which introduced an IC-based amplifier

called Gain Card. It was a paradigmatic shift in the philosophy of high-end amplifier design,

and it started a small revolution in the DIY world, with countless hobbyists confirming the

quality of its sonic performance.

The beauty of the IC amplifier is its simplicity. It is remarkably easy to build, and even

novice hobbyists can build a good sounding amplifier out of it. At the same time, it requires

just as much attention to details as any other amplifier to obtain the best possible

performance. With careful design and tuning, its sonic performance can truly blossom.

"Of all our human resources, the most precious is the desire to improve"

We started our own investigation by building several versions of IC power amplifiers based

on National Semiconductor's Overture series. Through our investigations, we discovered that

its potential had not yet been exhausted and that it could be pushed even more to a higher

level by optimizing the circuitry around it and the PCB layout. The result of this optimization

has demonstrated that the performance of an IC power amplifier can equal or exceed that of

expensive discrete designs. The only limitation is its moderate power capability, which still is

adequate for most home listening environment.



5

Key Advantages of IC Power Amplifiers:

What are the key advantages of IC power amplifiers over conventional discrete designs?

Three factors stand out:

Small Current Loops: With power amplifier ICs, a fully-functional amplifier can be

built using merely a handful of capacitors and resistors. This austerity lends itself to a

compact layout, with tiny current loop areas compared to discrete designs. Why is the loop

area important? The smaller the current loop, the less noise picked up by the circuit. The

inside of the amplifier enclosure is actually a noisy place, with lots of high-order harmonics

from the power supply (for Class AB amplifiers) and multiples of 60Hz from the transformer

floating around. Given such a noisy environment, the small loop area is a great antidote to

unwanted noise. The compactness of the IC power amplifier results in a very clean noise

floor, well below the realms of audibility.

Small Parasitic Capacitances and Inductances: The integrated-circuit technology

reduces drastically the capacitances and inductances associated with the layout. Within the

IC, wiring distances are orders of magnitude shorter compared to discrete designs. Also,

outside the IC, the layout can be compact, as already mentioned. All of this, along with the

sound circuit design of LM3886/4870, contributes to superior speed without resorting to

expensive technologies. Even with a 2uF capacitor load, just about the worst capacitive load

it will drive, the amplifier remains stable and well-behaved. Its excellent transient response

is well suited to driving all types of loudspeakers.

Close and Fast Thermal Tracking: Another key advantage of IC amplifiers is the

close thermal tracking of all the transistors. Since all the transistors are on the same chip, any

excessive heating in the output transistors can be detected fast and reliably, and actions can

be taken quickly to protect the amplifier and the loudspeaker (See National

Semiconductors Application Note AN-898 on SPiKe protection circuit). Moreover, the bias

devices for the output stage can track the output transistors closely in real time over a wide

range of temperatures. The result is consistent performance whether the amplifier is cold or

hot and whether it plays softly or loudly. The amplifiers settles into its optimum



6

Operating conditions. Within a few minutes of turn-on, and its performance remains solid

over a large range of temperatures and power levels.

These three factors, we believe, are the most significant ones that contribute to the excellent

performance of LM3886/4870 amplifiers.

Are there then any limitations to IC power amplifiers? The power handling capacity of a

single IC is moderate. But this is not an inherent limitation. The power output can be

increased significantly through the use of bridge and parallel techniques (See National

Semiconductor's Application Note AN-1192). Understandably, some are concerned about

thermal distortion, which arises from the heat generated in the output transistors flowing into

the input transistors. The first generation IC op amps indeed suffered from this effect, but

again, a significant progress has been made. By carefully controlling thermal gradients and

by using the common-centroid layout for the input devices, the thermal distortion can be

made negligible. If it is present, it would manifest itself as an increase in harmonic distortion

at low frequencies. In Anedio's implementation, no increase is observed, and the total

harmonic distortion at 20Hz remains below the threshold of measurement, about 0.0002%.

In conclusion, IC power amplifiers, such as the LM3886/4870, can be pushed to state-of-the-

art performance by carefully optimizing the circuitry around it and the PCB layout. And such

a level of performance can be achieved at a fraction of the cost of typical high-end

amplifiers, making them accessible to all audiophiles. Most important of all, it offers

exceptionally musical sound that engages the listener, powerful transients that communicate

the emotional impact, and extraordinary definition that draws the listener closer to live

performance.

TO SERVE THIS PURPOSE WE USE HERE IC LA 4440.



7

IC LA 4440 is a monolithic linear IC. It is a popular type of stereo amplifier with 6W-2

channel, Bridge 19W type power amplifier.

3.2 FEATURES:

• Built-in 2 channels (dual) enabling use in stereo and bridge amplifier applications.

Dual: 6W x 2 (typ.)

Bridge: 19W (typ.)

• Minimum number of external parts required.

• Small pop noise at the time of power supply ON/OFF and good starting balance.

• Good ripple rejection: 46dB (typ.)

• Good channel separation.

• Small residual noise (Rg=0).

• Low distortion over a wide range from low frequencies to high frequencies.

• Easy to design radiator fin.

• Built-in audio muting function.

• Built-in protectors.

a. Thermal protector

b. Overvoltage, surge voltage protector

c. Pin-to-pin short protector

PACKAGING DIMENSIONS:

Units: mm3023A-SIP14H

3.1.1 PACKAGING DIMENSIONS



8

3.3 SPECIFICATIONS AND OPERATING CHARACTERISTICS AT Ta=25°C:

Specifications:

Absolute Maximum Ratings at Ta = 25°C



9

3.3.1 CHARACTERISTICS OF IC LA 4440 AT Ta=25C



10

3.4 EQIVALENT IC CIRCUIT BLOCK DIAGRAM:

3.4.1 EQUIVALENT CIRCUIT BLOCK DIAGRAM OF IC



11

3.5 SAMPLE APPLICATION UNDER DIFFERENT OPERATING

MODES:

STEREO AMPLIFICATION MODE:

3.5.1 STEREO AMPLIFIER CIRCUIT

BRIDGE AMPLIFIER 1:

3.5.2 BRIDGE AMPLIFIER CKT-1



12

BRIDGE AMPLIFIER-2:

3.5.3 BRIDGE AMPLIFIER CKT-2

3.6 DESCRIPTION OF PIN DIAGRAM:

Features of IC System and Functions of Remaining Pins:

(a) Since the input circuit uses PNP transistors and the input potential is designed to be

0 bias, no input coupling capacitor is required and direct coupling is available. However,

when slider contact noise caused by the variable resistor presents a problem, connect a

capacitor in series with the input.

(b) The open-loop voltage gain is lowered and the negative feedback amount is reduced for

stabilization. An increase in distortion resulted from the reduced negative feedback

amount is avoided by use of the built-in unique distortion reduction circuit, and thus

distortion is kept at 0.1% (typ.).



(c) A capacitor for oscillation compensation is contained as a means of reducing the number

of external parts. The capacitance value is 35pF which determines high cutoff frequency

fH (– 3dB point) of the amplifier (fH»20kHz).

13

(d) For preventing the IC from being damaged by a surge applied on the power line, an

overvoltage protector is contained. Overvoltage setting is 25V. It is capable of

withstanding up to 50V at giant pulse surge 200ms.

(e) No damage occurs even when power is applied at a state where pins 10, 11, and 12 are

short-circuited with solder bridge, etc.

(f) To minimize the variations in voltage gain, feedback resistor RNF is contained and

voltage gain (51.5dB) is fixed.

3.7 VOLTAGE GAIN ADJUST AT DIFFERENT OPERATING MODES

VOLTAGE GAIN AT STEREO MODE:



3.7.1 VOLTAGE GAIN AT STEREO MODE

14

RNF=50W (typ), Rf=20kW (typ)

At RNF’=0 (recommended VG)

VG=20logVG/RNF (dB)

In case of using RNF’

VG=20logRf/(RNF1+RNF2) (dB)

VOLTAGE GAIN AT BRIDGE AMPLIFIER MODE:



3.7.2. VOLTAGE GAIN ADJUST AT BRIDGE AMPLILFIER-1

15

· The bridge amplifier configuration is as shown left, in which ch1 and ch2 operate as non-

inverting amplifier and inverting amplifier respectively.

The output of the non-inverting amplifier divided by resistors R3, R4 is applied, as input, to

the inverting amplifier.

Since attenuation (R4/R3) of the non-inverting amplifier output and amplification factor

(Rf/R4+RNF) of the inverting amplifier are fixed to be the same, signals of



the same level and 180° out of phase with each other can be obtained at output pins (12) and

(10). The total voltage gain is apparently higher than that of the non-inverting amplifier by

6dB and is approximately calculated by the following formula.

VG=20log +Rf/RNF 6dB

In case of reducing the voltage gain, RNF’ is connected

to the non-inverting amplifier side only and the following

formula is used.

VG=20log + RF/(RNF1+RNF2)6dB

16

3.8 PROPER CARE IN USING IC LA 4440: Proper Cares in Using IC

· Maximum ratings:

If the IC is used in the vicinity of the maximum ratings, even a slight variation in conditions

may cause the maximum ratings to be exceeded, thereby leading to breakdown. Allow an

ample margin of variation for supply voltage, etc. and use the IC in the range where the

maximum ratings are not exceeded.

Printed circuit board:



When making the board, refer to the sample printed circuit pattern and be careful that no

feedback loop is formed between input and output.

Oscillation preventing capacitor:

Normally, a polyester film capacitor is used for 0.1mF + 4.7W. The capacitance value can be

reduced to 0.047mF depending on the stability of the board·

Others:

Connect the radiator fin of the package to GND.

17

Proper Cares in Mounting Radiator Fin

1. The mounting torque is in the range of 39 to 59N-cm.

2. The distance between screw holes of the radiator fin must coincide with the distance

between screw holes of the IC.

With case outline dimensions L and R referred to, the screws must be tightened with the

distance between them as close to each other as possible.



3.8.1. HEAT SINK PIN PATTERN

3. The screw to be used must have a head equivalent to the one of truss machine screw or binder machine screw defined by JIS. Washers must be also used to protect the IC case.

4. No foreign matter such as cutting particles shall exist between heat sink and radiator fin. When applying grease on the junction surface, it must be applied uniformly on the whole surface.

5. IC lead pins are soldered to the printed circuit board after the radiator fin is mounted on

the IC.

18

4.1RESISTOR:

A resistor is a passive two-terminal electrical component that

implements electrical resistance as a circuit element. The current through a resistor is

in direct proportion to the across the resistor's terminals. Thus, the ratio of the voltage applied

across a resistor's terminals to the intensity of current through the circuit is called resistance.

This relation is represented by ohm`s law:



Where I is the current through the conductor in units of amperes V is the potential difference

measured across the conductor in units of volts,, and R is the resistance of the conductor in

units of ohms. More specifically, Ohm's law states that the R in this relation is constant,

independent of the current. Resistors are common elements of electrical and electronic

circuit and are ubiquitous in electronic equipment. Practical resistors can be made of various

compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such

as nickel-chrome). Resistors are also implemented within integrated circuits, particularly

analog devices, and can also be integrated into hybrid and printed circuits.

The electrical functionality of a resistor is specified by its resistance: common commercial

resistors are manufactured over a range of more than nine orders of magnitude. When

specifying that resistance in an electronic design, the required precision of the resistance may

require attention to the manufacturing tolerance of the chosen resistor, according to its

specific application. The temperature coefficient of the resistance may also be of concern in

some precision applications. Practical resistors are also specified as having a

maximum power rating which must exceed the anticipated power dissipation of that resistor

in a particular circuit: this is mainly of concern in power electronics applications.

19

Resistors with higher power ratings are physically larger and may require heat sinks. In a

high-voltage circuit, attention must sometimes be paid to the rated maximum working

voltage of the resistor.

Practical resistors have a series inductance and a small parallel capacitance; these

specifications can be important in high-frequency applications. In a low noise

amplifier or pre-amp, the noise characteristics of a resistor may be an issue. The unwanted

inductance, excess noise,



and temperature coefficient are mainly dependent on the technology used in manufacturing

the resistor. They are not normally specified individually for a particular family of resistors

manufactured using a particular technology. A family of discrete resistors is also

characterized according to its form factor, that is, the size of the device and the position of its

leads (or terminals) which is relevant in the practical manufacturing of circuits using them.

A resistor of 330 ohm serves our purpose of oscillatory preventing resistor in the noise filter.

4.1.1. RESISTOR 330 OHMS

20

4.2 CAPACITORS:

A capacitor (originally known as condenser) is a passive two-

terminal electrical component used to store energy in an electric field. The forms of practical

capacitors vary widely, but all contain at least two electrical conductors separated by

a dielectric (insulator); for example, one common construction consists of metal foils

separated by a thin layer of insulating film. Capacitors are widely used as parts of electrical

circuits in many common electrical devices.



When there is a potential difference (voltage) across the conductors, a static electric

field develops across the dielectric, causing positive charge to collect on one plate and

negative charge on the other plate. Energy is stored in the electrostatic field. An ideal

capacitor is characterized by a single constant value, capacitance, measured in farads. This is

the ratio of the electric charge on each conductor to the potential difference between them.

The capacitance is greatest when there is a narrow separation between large areas of

conductor, hence capacitor conductors are often called "plates," referring to an early means

of construction. In practice, the dielectric between the plates passes a small amount

of leakage current and also has an electric field strength limit, resulting in a breakdown

voltage, while the conductors and leads introduce an undesired inductance and resistance.

The capacitance is greatest when there is a narrow separation between large areas of

conductor, hence capacitor conductors are often called "plates," referring to an early means

of construction. In practice, the dielectric between the plates passes a small amount

of leakage current and also has an electric field strength limit, resulting in a breakdown

voltage, while the conductors and leads introduce an undesired inductance and resistance.

21

Various capacitors employed here in noise filter are:



2200uf/25v capacitor: 100uf/25vcapacitor:

47uf/25v capacitor: 0.1uf capacitor:

330uf/25v capacitor:

4.2.1. VARIOUS CAPACITORS

22

4.3 SPEAKERS:



A loudspeaker (or "speaker") is an electro acoustic transducer that

produces sound in response to an electrical audio signal input. Non-electrical loudspeakers

were developed as accessories to telephone systems, but electronic amplification by vacuum

tube made loudspeakers more generally useful. The most common form of loudspeaker uses

a paper cone supporting a voice coil electromagnet acting on a permanent magnet, but many

other types exist. Where accurate reproduction of sound is required, multiple loudspeakers

may be used, each reproducing a part of the audible frequency range. Miniature loudspeakers

are found in devices such as radio and TV receivers, and many forms of music players.

Larger loudspeaker systems are used for music, sound reinforcement in theatres and concerts,

and in public address systems.

4.3.1 LOUD SPEAKERS

23

5.1 COMPONENTS USED IN LAPTOP AUDIO AMPLIFIER:



1. IC LA 4440

2. RESISTORS- 330 OHMS (2x)

3. CAPACITORS- 2200uf/25v (1x), 100uf/25v (2x), 330uf/25v (3x), 47uf/25v(2x)

4. INTER CONNECTING WIRES

5. GENERAL PURPOSE PCB

5.2 EQUIVALENT CIRCUIT:

5.2.1 EQUIVALENT CKT AMPLIFIER DIAGRAM

24



5.3 DESCRIPTION OF EXTERNAL PARTS:

C1- Power source capacitor.

C2 · De-coupling capacitor: Used for the ripple filter. Since the rejection effect is saturated at

a certain capacitance value, it is meaningless to increase the capacitance value more than

required. This capacitor, being also used for the time constant of the muting circuit, affects

the starting time.

C3 (C4) · Feedback capacitor: The low cutoff frequency depends on this capacitor.

If the capacitance value is increased, the starting time is delayed.

C5 (C8) · Bootstrap capacitor: If the capacitance value is decreased, the output at low

frequencies goes lower.

C6 (C9) · Oscillation preventing capacitor: Polyester film capacitor, being good in

temperature characteristic, frequency characteristic, is used.

The capacitance value can be reduced to 0.047mF depending on the stability of the board.

C7 (C10) · Output capacitor: The low cutoff frequency depends on this capacitor.

At the bridge amplifier mode, the output capacitor is generally connected.

R1 (R2) · Filter resistor for preventing oscillation.

Ls1 (Ls2) - loud speakers: given as load to the circuit for audio enhancement purpose.

25



5.4 PCB LAYOUT:

5.4.1 PCB Layout

26



6.1 WORKING PROCEDURE:

The project Laptop Audio Amplifier is exclusive project that enables the user to enhance the

sound output from laptop audio speakers.

The working of the project starts when the stereo is interfaced with Laptop through Audio

Jack Cable which is in connected to the amplifier circuit. The problem comes into picture

when one tries to address a group of people either in a presentation purposes or in conference

hall. The in built sound from an integrated laptop speaker may not be audible till the last

sitters, this retrieves the attention of listeners.

To avoid this situation one may use locally built self speaker amplifiers but those many

drawbacks, they provide sound output of poor quality, with Total Harmonic Distortion of 3%

or more and power output of 4watts per channel. These factors limit the usage of such

speakers.

This problem can be avoided with simple Usage a Laptop audio amplifier circuit build by

using IC LA 4440 which provide a power output of 6w per channel, operates in frequency

range of

23khz-18,000khz with a minimal THD of 1%.

27



FOLLOWING STEPS OF SEQUENCE ARE EMPLOYED:

1.) Connect the stereo and Laptop interface to the circuit such that the right channel input is

given to pin no.2 and left channel input is given to pin no.6.

2.) Pin no.2 along with the NF1 (negative feednack1) placed at pin 1, voltage derived from a

capacitor of 47uf is given as input to a differential amplifier in-built in the IC.

3.) Pin no.6 along with NF2 (negative feedback 2) placed at pin 7, voltage derived from a

capacitor of 47uf is given as input to a differential amplifier in-built in the IC.

4.) The output from the op-amp is given to driver amplifier because the output from the op-

amp are not sufficient to driver load in the form of speakers.

5.) The output from the driver amplifier is given to a output amplifier, where these placed are

observed in-built in IC.

6.) The pin no.5 provides route for ripple filter.

7.) The pin no.4 is muting pin, which is connected in pin no.7 of both op-amps inside the

IC`s.

28 -----------------------------------------------------------------------------------------------------



6.2 ADVANTAGES:

All the drawbacks of in-built speakers in a Integrated laptop system are overcome by the

design of Laptop audio amplifier.

1.) FREQUENCY RANGE:

We know that the perfect human hearing range is 20khz-20,000khz because of

limitations in a normal speaker system we obtained a output range of 100khz-

23,000khz.

By the use of this laptop audio amplifier, we have successfully obtained a Frequency

range of around 23khz-18,000khz.

2.) POWER OUTPUT:

An Ideal Speaker Is Assumed To Provide A High Output Of Around 6w-8w.

We here satisfactorily designed a power output of 6wx2 channels.

3.) Total Harmonic Distortion:

Audio signals of THD around 0.1% or less are only acceptable. The laptop audio is

generally produces a THD of 10%, the laptop audio amplifier produces audio of

around of 0.5%-1%.

29



6.3 APPLICATIONS:

1.) It can be used of general laptop purposes.

2.) Used in sound mixing-

For sound output of -0.1DBFS

3.) Used in Re-Recording purpose especially for Low Quality speech signals.

4.) It can also used to serve both as stereo and mono amplifier.

30



6.4 CONCLUSION:

The Project “Laptop Audio Amplifier” has been successfully designed and tested.

Integrating features of all the hardware components used have developed it.

Presence of all reasoned out and placed carefully thus contributing to the best working of the

unit. Secondly, using highly advanced IC`s and with the help of growing technology the

project has been successfully designed.

Hence this project provides a better solution for the users to amplify

their Audio output from Laptops.

31



6.5 BIBLIOGRAPHY:

1.) www.wikipedia.com

2.) www.daasheetarcheive.com

3.) www.electronicsforu.com

4.) UPGRADING AND REPAIRING LAPTOPS- SCOTT MUELER

5.) http://hyperphysics.phy-astr.gsu.edu/hbase/audio/spk.html

6.) www.circuitsector.com/.../simple-laptop-audio-amplifier-circuit.html

7.) PERIPHERAL COMPONENTS-D.E.V PRASAD

32



APPENDIX:

33



34



35



36


laptop audio amplifier

Documents

audio jack

laptop audio

polyester

bridge amplifier

total harmonic

ic power amplifiers

oscillation

printed circuit