History of CDMA

8/4/2019 History of CDMA

1/45

1. CDMA

Code division multiple access (CDMA) is a form of

multiplexing (not a modulation scheme) and a method ofmultiple

access that does not divide up the channel by time (as in

TDMA), or frequency (as in FDMA), but instead encodes data

with a certain code associated with a channel and uses the

constructive interference properties of the signal medium to

perform the multiplexing. CDMA also refers to digital cellular

telephony systems that make use of this multiple access

scheme, such as those pioneered by Qualcomm, orW-CDMA.

1.1 Usage in mobile telephony

A number of different terms are used to refer to CDMA

implementations. The original standard spearheaded by

QUALCOMM was known as IS-95, the IS referring to an Interim

Standard of the Telecommunications Industry Association (TIA).

IS-95 is often referred to as 2G or second generation cellular.

The QUALCOMM brand name cdma One may also be used to

refer to the 2G CDMA standard.

After a couple of revisions, IS-95 was superseded by the IS-

2000 standard. This standard was introduced to meet some of

the criteria laid out in the IMT-2000 specification for 3G, or third

generation, cellular. It is also referred to as 1xRTT which simply

means "1 times Radio Transmission Technology" and indicates

that IS-2000 uses the same 1.25-MHz shared channel as the

1
http://en.wikipedia.org/wiki/Multiple_accesshttp://en.wikipedia.org/wiki/Multiple_accesshttp://en.wikipedia.org/wiki/Timehttp://en.wikipedia.org/wiki/TDMAhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/FDMAhttp://en.wikipedia.org/wiki/Constructive_interferencehttp://en.wikipedia.org/wiki/Cellular_networkhttp://en.wikipedia.org/wiki/Cellular_networkhttp://en.wikipedia.org/wiki/Qualcommhttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/QUALCOMMhttp://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/IMT-2000http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/Multiple_accesshttp://en.wikipedia.org/wiki/Multiple_accesshttp://en.wikipedia.org/wiki/Timehttp://en.wikipedia.org/wiki/TDMAhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/FDMAhttp://en.wikipedia.org/wiki/Constructive_interferencehttp://en.wikipedia.org/wiki/Cellular_networkhttp://en.wikipedia.org/wiki/Cellular_networkhttp://en.wikipedia.org/wiki/Qualcommhttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/QUALCOMMhttp://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/IMT-2000http://en.wikipedia.org/wiki/CDMA2000


2/45

original IS-95 standard. A related scheme called 3xRTT uses

three 1.25-MHz carriers for a 3.75-MHz bandwidth that would

allow higher data burst rates for an individual user, but the

3xRTT scheme has not been commercially deployed.

More recently, QUALCOMM has led the creation of a new

CDMA-based technology called 1xEV-DO, or IS-856, which

provides the higher packet data transmission rates required by

IMT-2000 and desired by wireless network operators.

The QUALCOMM CDMA system includes highly accurate time

signals (usually referenced to a GPS receiver in the cell base

station), so cell phone CDMA-based clocks are an increasingly

popular type of radio clock for use in computer networks. The

main advantage of using CDMA cell phone signals for reference

clock purposes is that they work better inside buildings, thus

often eliminating the need to mount a GPS antenna on the

outside of a building.

Also frequently confused with CDMA is W-CDMA. The CDMA

technique is used as the principle of the W-CDMA air interface,

and the W-CDMA air interface is used in the global 3G standard

UMTS and the Japanese 3G standard FOMA, by NTT DoCoMo

and Vodafone; however, the CDMA family of standards

(including cdmaOne and CDMA2000) are not compatible with

the W-CDMA family of standards.

Another important application of CDMApredating and entirely

distinct from CDMA cellularis the Global Positioning System,

GPS.

2
http://en.wikipedia.org/wiki/Evolution-Data_Optimizedhttp://en.wikipedia.org/wiki/Radio_clockhttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/UMTShttp://en.wikipedia.org/wiki/FOMAhttp://en.wikipedia.org/wiki/NTT_DoCoMohttp://en.wikipedia.org/wiki/Vodafonehttp://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/GPShttp://en.wikipedia.org/wiki/Evolution-Data_Optimizedhttp://en.wikipedia.org/wiki/Radio_clockhttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/UMTShttp://en.wikipedia.org/wiki/FOMAhttp://en.wikipedia.org/wiki/NTT_DoCoMohttp://en.wikipedia.org/wiki/Vodafonehttp://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/GPS


3/45

1.2 Coverage

As CDMA is newer than GSM, it may not be available in some

parts of the world. However, as the signal can be transmitted

over greater distances, it may give reception in more remote or

rural areas where a GSM phone does not pick up a signal.

1.3 Mathematical foundation

CDMA exploits at its core mathematical properties of

orthogonality. Suppose we represent data signals as vectors.

For example, the binary string "1011" would be represented by

the vector (1, 0, 1, 1). We may wish to give a vector a name, we

may do so by using boldface letters, eg a. We also use an

operation on vectors, known as the dot product, to "multiply"

vectors, by summing the product of the components. For

example, the dot product of (1, 0, 1, 1) and (1, -1, -1, 0) would

be (1)(1)+(0)(-1)+(1)(-1)+(1)(0)=1+-1=0. Where the dot product

of vectors a and b is 0, we say that the two vectors are

orthogonal.

The dot product has a number of properties, and one will aid us

in understanding why CDMA works. For vectors a, b, c:

3
http://en.wikipedia.org/wiki/Orthogonalityhttp://en.wikipedia.org/wiki/Coordinate_vectorhttp://en.wikipedia.org/wiki/Dot_producthttp://en.wikipedia.org/wiki/Orthogonalityhttp://en.wikipedia.org/wiki/Coordinate_vectorhttp://en.wikipedia.org/wiki/Dot_product


4/45

The square root of a.a is a real number, and is important. We

write

Suppose vectors a and b are orthogonal. Then:

4


5/45

1.4 Implementation

An example of 4 orthogonal digital signals.

Suppose now we have a set of vectors that are mutually

orthogonal to each other. Usually these vectors are specially

constructed for ease of decoding -- they are columns or rows

from Walsh matrices that are constructed from Walsh functions

-- but strictly mathematically the only restriction on these vectors

is that they are orthogonal. An example of orthogonal functions

5
http://en.wikipedia.org/wiki/Walsh_matrixhttp://en.wikipedia.org/wiki/Walsh_functionhttp://en.wikipedia.org/wiki/Image:Cdma_orthogonal_signals.pnghttp://en.wikipedia.org/wiki/Walsh_matrixhttp://en.wikipedia.org/wiki/Walsh_function


6/45

is shown in the picture on the right. Now, associate with one

sender a vector from this set, say v, which is called the chip

code. Associate a zero digit with the vector -v, and a one digit

with the vectorv. For example, ifv=(1,-1), then the binary vector

(1, 0, 1, 1) would correspond to (1,-1,-1,1,1,-1,1,-1). For the

purposes of this article, we call this constructed vector the

transmitted vector.

Each sender has a different, unique vector chosen from that set,

but the construction of the transmitted vector is identical.

Now, the physical properties of interference say that if two

signals at a point are in phase, they will "add up" to give twice

the amplitude of each signal, but if they are out of phase, they

will "subtract" and give a signal that is the difference of the

amplitudes. Digitally, this behaviour can be modelled simply by

the addition of the transmission vectors, componentwise. So, if

we have two senders, both sending simultaneously, one with thechip code (1, -1) and data vector (1, 0, 1, 1), and another with

the chip code (1, 1), and data vector (0,0,1,1), the raw signal

received would be the sum of the transmission vectors (1,-1,-

1,1,1,-1,1,-1)+(-1,-1,-1,-1,1,1,1,1)=(0,-2,-2,0,2,0,2,0).

Suppose a receiver gets such a signal, and wants to detect what

the transmitter with chip code (1, -1) is sending. The receiver

will make use of the property described in the above foundation

section, and take the dot product to the received vector in parts.

Take the first two components of the received vector, that is, (0,

-2). Now, (0, -2).(1, -1) = (0)(1)+(-2)(-1) = 2. Since this is

6
http://en.wikipedia.org/wiki/Chiphttp://en.wikipedia.org/wiki/Chip


7/45

positive, we can deduce that a one digit was sent. Taking the

next two components, (-2, 0), (-2, 0).(1,-1)=(-2)(1)+(0)(-1)=-2.

Since this is negative, we can deduce that a zero digit was sent.

Continuing in this fashion, we can successfully decode what the

transmitter with chip code (1, -1) was sending: (1, 0, 1,

1).Likewise, applying the same process with chip code (1, 1): (1,

1).(0,-2) = -2 gives digit 0, (1, 1).(-2,0)=(1)(-2)+(1)(0)=-2 gives

digit 0, and so on, to give us the data vector sent by the

transmitter with chip code (1, 1): (0, 0, 1, 1).

Now, there are certain issues where this mathematical processcan be disrupted. Suppose that one sender transmits at a higher

signal strength than another. Then the critical orthogonality

property can be disrupted, and thus the system can fail. Thus

controlling power strength is an important issue with CDMA

transmitters. A TDMA or FDMA receiver can in theory

completely reject arbitrarily strong signals on other time slots or

frequency channels. This is not true for CDMA; rejection of

unwanted signals is only partial. If any or all of the unwanted

signals are much stronger than the desired signal, they will

overwhelm it. This leads to a general requirement in any CDMA

system to approximately match the various signal power levels

as seen at the receiver. In CDMA cellular, the base station uses

a fast closed-loop power control scheme to tightly control each

mobile's transmit power.

Suppose that noise present in a channel takes a zero bit to

some other value. Then this will also disrupt the orthogonality

7


8/45

property, and thus adding an extra level of forward error

correction (FEC) coding is also vital.

So far, we have assumed that CDMA timing is absolutely exact,

that is, transmitters exactly transmit at points in multiples of the

length of the chip sequence. Of course, in reality, this is

impractical to achieve, so all forms of CDMA use spread

spectrumprocess gain to allow receivers to partially discriminate

against unwanted signals. Signals with the desired chip code

and timing are received, while signals with different chip codes

(or the same spreading code but a different timing offset) appear

as wideband noise reduced by the process gain.

CDMA's main advantage over TDMA and FDMA is that the

number of available CDMA codes is essentially infinite. This

makes CDMA ideally suited to large numbers of transmitters

each generating a relatively small amount of traffic at irregular

intervals, as it avoids the overhead of continually allocating and

deallocating a l imited number of orthogonal time slots or

frequency channels to individual transmitters. CDMA

transmitters simply send when they have something to say, and

go off the air when they don't.

8
http://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/Process_gainhttp://en.wikipedia.org/wiki/Orthogonalhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/Process_gainhttp://en.wikipedia.org/wiki/Orthogonal


9/45

1.5 CDMA features

Narrowband message signal multiplied by wideband

spreading signal orpseudo-noise code

Each user has his own pseudo-noise (PN) code

Soft capacity limit: system performance degrades for all

users as number of users increases

Cell frequency reuse: no frequency planning needed

Soft handoffincreases capacity

Near-far problem

Interference limited: power control is required

Wide bandwidth induces diversity: rake receiveris used

It would take all the computers ever made as much time as

humans have been on earth to crack or decode a single

second of CDMA conversation

9
http://en.wikipedia.org/wiki/Pseudorandom_noisehttp://en.wikipedia.org/wiki/Handoffhttp://en.wikipedia.org/wiki/Near-far_problemhttp://en.wikipedia.org/wiki/Rake_receiverhttp://en.wikipedia.org/wiki/Pseudorandom_noisehttp://en.wikipedia.org/wiki/Handoffhttp://en.wikipedia.org/wiki/Near-far_problemhttp://en.wikipedia.org/wiki/Rake_receiver


10/45

10


11/45

11


12/45

12


13/45

2. Capacitors

The capacitor's function is to store electricity, or electrical

energy. The capacitor also functions as a filter, passing

alternating current (AC), and blocking direct current (DC). This

symbol is used to indicate a capacitor in a circuit diagram.

The capacitor is constructed with two electrode plates facing

each other, but separated by an insulator. When DC voltage is

applied to the capacitor, an electric charge is stored on each

electrode. While the capacitor is charging up, current flows. The

current will stop flowing when the capacitor has fully charged.

The capacitance of a capacitor is generally very small, so units

such as the microfarad ( 10-6F ), nanofarad ( 10-9F ) , and

picofarad (10-12F) are used.

The capacitor has an insulator ( the dielectric ) between 2

sheets of electrodes. Different kinds of capacitors use different

materials for the dielectric.

2.1 Electrolytic Capacitors (Electrochemical

capacitors)

Aluminum is used for the electrodes by using a thin oxidizationmembrane. Large values of capacitance can be obtained in

comparison with the size of the capacitor, because the dielectric

used is very thin. The most important characteristic of

electrolytic capacitors is that they have polarity. They have a

13


14/45

positive and a negative electrode.[Polarised] This means that it

is very important which way round they are connected. If the

capacitor is subjected to voltage exceeding its working voltage,

or if it is connected with incorrect polarity, it may burst. It is

extremely dangerous, because it can quite literally explode.

Make absolutely no mistakes. Generally, in the circuit diagram,

the positive side is indicated by a "+" (plus) symbol. Electrolytic

capacitors range in value from about 1F to thousands of F.

Mainly this type of capacitor is used as a ripple filter in a power

supply circuit, or as a filter to bypass low frequency signals, etc.

Because this type of capacitor is comparatively similar to the

nature of a coil in construction, it isn't possible to use for high-

frequency circuits. (It is said that the frequency characteristic is

bad.) The photograph on the left is an example of the different

values of electrolytic capacitors in which the capacitance and

voltage differ. From the left to right: 1F (50V) [diameter 5 mm,

high 12 mm] 47F (16V) [diameter 6 mm, high 5 mm] 100F

(25V) [diameter 5 mm, high 11 mm] 220F (25V) [diameter 8

mm, high 12 mm] 1000F (50V) [diameter 18 mm, high 40 mm]

The size of the capacitor sometimes

14


15/45

depends on the manufacturer. So the sizes shown here on this

page are just examples. In the photograph to the right, the mark

indicating the negative lead of the component can be seen. You

need to pay attention to the polarity indication so as not to make

a mistake when you assemble the circuit.

2.2 Ceramic Capacitors

Ceramic capacitors are constructed with materials such as

titanium acid barium used as the dielectric. Internally, these

15


16/45

capacitors are not constructed as a coil, so they can be used in

high frequency

applications. Typically, they are used in circuits which bypass

high frequency signals to ground. These capacitors have the

shape of a disk. Their capacitance is comparatively small. The

capacitor on the left is a 100pF capacitor with a diameter of

about 3 mm.The capacitor on the right side is printed with 103,

so 10 x 103pF becomes 0.01 F. The diameter of the disk is

about 6 mm. Ceramic capacitors have no polarity. Ceramic

capacitors should not be used for analog circuits, because they

can distort the signal. Multilayer Ceramic Capacitors The

multilayer ceramic capacitor has a many-layered dielectric.

These capacitors are small in size, and have good temperatureand frequency characteristics. Square wave signals used in

digital circuits can have a comparatively high frequency

component included. This capacitor is used to bypass the high

frequency to ground. In the photograph, the capacitance of the

16


17/45

component on the left is displayed as 104. So, the capacitance

is 10 x 104 pF = 0.1 F. The thickness is 2 mm, the height is 3

mm, the width is 4 mm.The capacitor to the right has a

capacitance of 103 (10 x 103 pF = 0.01 F). The height is 4 mm,

the diameter of the round part is 2 mm. These capacitors are not

polarized. That is, they have no polarity.

2.3 Polystyrene Film Capacitors

In these devices, polystyrene film is used as the dielectric. Thistype of capacitor is not for use in high frequency circuits,

because they are constructed like a coil inside. They are used

well in filter circuits or timing circuits which run at several

hundred KHz or less. The component shown on the left has a

red color due to the copper leaf used for the electrode. The

silver color is due to the use of aluminum foil as the electrode.

The device on the left has a height of 10 mm, is 5 mm thick, and

is rated 100pF. The device in the middle has a height of 10 mm,

5.7 mm thickness, and is rated The device on the right has a

height of 24 mm, is 10 mm thick, and is rated 10000pF. These

devices have no polarity.

17


18/45

This capacitor is used when a higher tolerance is necessary

than polyester capacitors offer. Polypropylene film is used for

the dielectric. It is said that there is almost no change of

capacitance in these devices if they are used with frequencies of

100KHz or less. The pictured capacitors have a tolerance of

1%. From the left in the photograph Capacitance: 0.01 F

(printed with 103F) [the width 7mm, the height 7mm, the

thickness 3mm]Capacitance: 0.022 F (printed with 223F) [the

width 7mm, the height 10mm, the thickness 4mm]Capacitance:

0.1 F (printed with 104F) [the width 9mm, the height 11mm, the

thickness 5mm] When I measured the capacitance of a 0.01 F

capacitor with the meter which I have, the error was +0.2%.

These capacitors have no polarity.

2.4 Variable CapacitorsVariable capacitors are used for adjustment etc. of frequency

mainly. On the left in the photograph is a "trimmer," which uses

18


19/45

ceramic as the dielectric. Next to it on the right is one that uses

polyester film for the dielectric.

The pictured components are meant to be mounted on a printed

circuit board.

When adjusting the value of a variable capacitor, it is advisable

to be careful. One of the component's leads is connected to the

adjustment screw of the capacitor. This means that the value of

the capacitor can be affected by the capacitance of the

screwdriver in your hand. It is better to use a special screwdriver

to adjust these components. Pictured in the upper left

photograph are variable capacitors with the following

specifications: Capacitance: 20pF (3pF - 27pF measured)

[Thickness 6 mm, height 4.8 mm]Their are different colors, as

well. Blue: 7pF (2 - 9), white: 10pF (3 - 15), green: 30pF (5 - 35),

brown: 60pF (8 - 72). In the same photograph, the device on the

right has the following specifications: Capacitance: 30pF (5pF -40pF measured) [The width (long) 6.8 mm, width (short) 4.9 mm,

and the height 5 mm] The components in the photograph on the

right are used for radio tuners, etc. They are called "Varicons"

but this may be only in Japan. The variable capacitor on the left

in the photograph, uses air as the dielectric. It combines three

independent capacitors. For each one, the capacitance changed

2pF - 18pF. When the adjustment axis is turned, the capacitance

of all 3 capacitors change simultaneously. Physically, the device

has a depth of 29 mm, and 17 mm width and height. (Not

including the adjustment rod.) There are various kinds of

19


20/45

variable capacitor, chosen in accordance with the purpose for

which they are needed. The pictured components are very small.

To the right in the photograph is a variable capacitor using

polyester film as the dielectric. Two independent capacitors are

combined. The capacitance of one side changes 12pF - 150pF,

while the other side changes from 11pF - 70pF. Physically, it

has a depth of 11mm, and 20mm width and height. (Not

including the adjustment rod.) The pictured device also has a

small trimmer built in to each capacitor to allow for precise

adjustment up to 15pF.

3. Coils

20


21/45

A coil is nothing more than copper wire wound in a spiral. This

symbol is used to indicate a coil in a circuit diagram.

Inductance value is designated in units called the Henry(H). The

more wire the coil contains, the stronger its characteristics

become. The inductance value can become quite large. If a coil

is wound around an iron rod, or ferrite core (strengthened with

iron powder), the inductance of the coil will be greatly increased.

Coils used in typical electric circuits varely widely in values,

ranging from a few micro-henry (H) to many henry (H). Coils

are sometimes called "inductors." Inductance is the measure ofthe strength of a coil. Capacitors have capacitance, resistors

have resistance, and Inductors (coils) have inductance. When

alternating current flows through a coil, the magnetic flux that

occurs in the coil changes with the current. When a second coil

is put close to the first coil (with the changing flux), alternating

voltage is caused to flow in the second coil by an effect known

as "mutual induction." Mutual inductance (inductance) is

measured in units of the Henry. The changing magnetic flux in a

coil affects itself as well as other coils. This is called self

induction, the degree of this self induction is called Self

Inductance. Self inductance is a measure of a coil's ability to

establish an induced voltage as a result of a change in its

current. Self inductance is commonly referred to as simply

"inductance," and is symbolized by "L". The unit of inductance is

the Henry (H).

21


22/45

The definition of "Henry" is "When a current of 1 ampere flows

through a given coil in 1 second such that 1 volt is induced to

flow in a second coil, the mutual inductance between the coils is

said to be 1 Henry." The definition of self inductance is the

same, except that the 1 volt is induced in the first coil; there is

no second coil.

Characteristic of coils When wire is coiled, it takes on various

characteristics that are different from straight wire. Below I will

explain some of the characteristics coils that I know. Current

Stabilization Characteristic When current begins to flow in the

coil, the coil resists the flow. When current decreases, the coil

makes current continue to flow (briefly) at the previous rate. This

is called " Lenz's law ".The direction of induced current in a coil

is such that is opposes the change in the magnetic field that

produced it.

This characteristic is used for the ripple filter circuit of a power

supply where it transforms alternating current(AC) to direct

current(DC).When a rectifier is used to make DC from AC, the

output of the rectifier without a ripple filter circuit is ripple

current. Ripple current is DC that has a large AC component. Aripple filter circuit often combines coil and capacitors. The coil

resists the change of current and capacitors supplement the flow

of current by discharging into the circuit if the input voltage

drops. Thus, clear, ripple-free DC is obtained from the ripple

22


23/45

filter circuit. Resistor is used instead of coil in simple ripple filter

circuit. Mutual induction

23


24/45

4. DiodesA diode is a semiconductor device which allows current to flow

through it in only one direction. Although a transistor is also a

semiconductor device, it does not operate the way a diode does.

A diode is specifically made to allow current to flow through it in

only one direction. Some ways in which the diode can be used

are listed here. A diode can be used as a rectifier that converts

AC (Alternating Current) to DC (Direct Current) for a power

supplydevice.

Diodes can be used to separate the signal from radio

frequencies

Diodes can be used as an on/off switch that controls current.

This symbol is used to indicate a diode in a circuit diagram.

The meaning of the symbol is (Anode) (Cathode). Current

flows from the anode side to the cathode side. Although all

diodes operate with the same general principle, there are

different types suited to different applications. For example, the

following devices are best used for the applications noted.

4.1 Light emitting diodeThe circuit symbol is .This type of diode emits light when current

flows through it in the forward direction. (Forward biased.)

24


25/45

4.2 Variable capacitance diode

The circuit symbol is .The current does not f low when

applying the voltage of the opposite direction to the diode. In

this condition, the diode has a capacitance like the capacitor. It

is a very small capacitance. The capacitance of the diode

changes when changing voltage. With the change of this

capacitance, the frequency of the oscillator can be changed.

25


26/45

The graph on the right shows the electrical characteristics of a

typical diode. When a small voltage is applied to the diode in

the forward direction, current flows easily. Because the diodehas a certain amount of resistance, the voltage will drop slightly

as current flows through the diode. A typical diode causes a

voltage drop of about 0.6 - 1V (VF) (In the case of silicon diode,

almost 0.6V) This voltage drop needs to be taken into

consideration in a circuit which uses many diodes in series.

Also, the amount of current passing through the diodes must be

considered. When voltage is applied in the reverse direction

through a diode, the diode will have a great resistance to current

flow. Different diodes have different characteristics when

reverse-biased. A given diode should be selected depending on

how it will be used in the circuit. The current that will flow

through a diode biased in the reverse direction will vary from

several mA to just A, which is very small. The limiting voltages

and currents permissible must be considered on a case by case

basis. For example, when using diodes for rectification, part of

the time they will be required to withstand a reverse voltage. If

the diodes are not chosen carefully, they will break down.

26


27/45

4.3 Rectification/Switching/RegulationDiode

The stripe stamped on one end of the diode shows indicates the

polarity of the diode. The stripe shows the cathode side. The top

two devices shown in the picture are diodes used for

rectification. They are made to handle relatively high currents.

The device on top can handle as high as 6A, and the one below

it can safely handle up to 1A. However, it is best used at about

70% of its rating because this current value is a maximum

rating. The third device from the top (red color) has a part

27


28/45

number of 1S1588. This diode is used for switching, because it

can switch on and off at very high speed. However, the

maximum current it can handle is 120 mA. This makes it well

suited to use within digital circuits. The maximum reverse

voltage (reverse bias) this diode can handle is 30V. The device

at the bottom of the picture is a voltage regulation diode with a

rating of 6V. When this type of diode is reverse biased, it will

resist changes in voltage. If the input voltage is increased, the

output voltage will not change. (Or any change will be an

insignificant amount.) While the output voltage does not

increase with an increase in input voltage, the output current

will. This requires some thought for a protection circuit so that

too much current does not flow. The rated current limit for the

device is 30 mA.

28


29/45

Generally, a 3-terminal voltage regulator is used for the

stabilization of a power supply. Therefore, this diode is typically

used to protect the circuit from momentary voltage spikes. 3

terminal regulators use voltage regulation diodes inside.

4.4 Diode bridge

Rectification diodes are used to make DC from AC. It is possible

to do only 'half wave rectification' using 1 diode. When 4 diodes

are combined, 'full wave rectification' occurrs. Devices that

combine 4 diodes in one package are called diode bridges. They

are used for full-wave rectification. Physically, it is 7 mm high,

and 10 mm in diameter. The flat device on the left has a current

29


30/45

limit of 4A. It is has a thickness of 6 mm, is 16 mm in height, and

19 mm in width.The photograph on the right shows a large, high-

power diode bridge. It has a current capacity of 15A. The peak

reverse-bias voltage is 400V. Diode bridges with large current

capacities like this one, require a heat sink. Typically, they are

screwed to a piece of metal, or the chasis of device in which

they are used. The heat sink allows the device to radiate excess

heat. As for size, this one is 26 mm wide on each side, and the

height of the module part is 10 mm.

4.5 Light Emitting Diode ( LED )

Light emitting diodes must be choosen according to how they

will be used, because there are various kinds. The diodes are

available in several colors. The most common colors are red and

green, but there are even blue ones. The device on the far right

30


31/45

in the photograph combines a red LED and green LED in one

package. The component lead in the middle is common to both

LEDs. As for the remaing two leads, one side is for the green,

the other for the red LED. When both are turned on

simultaneously, it becomes orange. When an LED is new out of

the package, the polarity of the device can be determined by

looking at the leads. The longer lead is the Anode side, and the

short one is the Cathode side. The polarity of an LED can also

be determined using a resistance meter, or even a 1.5 V battery.

When using a test meter to determine polarity, set the meter to a

low resistance measurement range. Connect the probes of the

meter to the LED. If the polarity is correct, the LED will glow. If

the LED does not glow, switch the meter probes to the opposite

leads on the LED. In either case, the side of the diode which is

connected to the black meter probe when the LED glows, is the

Anode side. Positive voltage flows out of the black probe when

the meter is set to measure resistance. It is possible to use

an LED to obtain a fixed voltage. The voltage drop (forward

voltage, or VF) of an LED is comparatively stable at just about

2V.

31


32/45

5. Transistors

The transistor's function is to amplify an electric current. Many

different kinds of transistors are used in analog circuits, fordifferent reasons. This is not the case for digital circuits. In a

digital circuit, only two values matter; on or off. The amplification

abilitiy of a transistor is not relevant in a digital circuit. In many

cases, a circuit is built with integrated circuits(ICs). Transistors

are often used in digital circuits as buffers to protect ICs. For

example, when powering an electromagnetic switch (called a

'relay'), or when controlling a light emitting diode. (In my case.)

Two different symbols are used for the transistor. PNP type

and NPN type

The name (standard part number) of the transistor, as well as

the type and the way it is used is shown below.

2SAXXXX PNP type high frequency 2SBXXXX PNP type low

frequency 2SCXXXX NPN type high frequency 2SDXXXX NPN

type low frequency

The direction of the current flow differs between the PNP and

NPN type.When the power supply is the side of the positive

(plus), the NPN type is easy to use.

32


33/45

6. Resistors

The resistor's function is to reduce the flow of electric current.

This symbol is used to indicate a resistor in a circuit

diagram, known as a schematic. Resistance value is designated

in units called the "Ohm." A 1000 Ohm resistor is typically

shown as 1K-Ohm ( kilo Ohm ), and 1000 K-Ohms is written as

1M-Ohm ( megohm ). There are two classes of resistors; fixed

resistors and the variable resistors . They are also classified

according to the material from which they are made. The typical

resistor is made of either carbon film or metal film. There are

other types as well, but these are the most common. The

resistance value of the resistor is not the only thing to consider

when selecting a resistor for use in a circuit. The "tolerance" and

the electric power ratings of the resistor are also important. The

tolerance of a resistor denotes how close it is to the actual ratedresistence value. For example, a 5% tolerance would indicate a

resistor that is within 5% of the specified resistance value. The

power rating indicates how much power the resistor can safely

tolerate. Just like you wouldn't use a 6 volt flashlight lamp to

replace a burned out light in your house, you wouldn't use a 1/8

watt resistor when you should be using a 1/2 watt resistor. The

maximum rated power of the resistor is specified in Watts.

Power is calculated using the square of the current ( I2 ) x the

resistance value ( R ) of the resistor. If the maximum rating of

the resistor is exceeded, it will become extremely hot, and even

33
http://www.interq.or.jp/japan/se-inoue/e_resistor.htm#fixhttp://www.interq.or.jp/japan/se-inoue/e_resistor.htm#fixhttp://www.interq.or.jp/japan/se-inoue/e_resistor.htm#variablehttp://www.interq.or.jp/japan/se-inoue/e_resistor.htm#fixhttp://www.interq.or.jp/japan/se-inoue/e_resistor.htm#fixhttp://www.interq.or.jp/japan/se-inoue/e_resistor.htm#variable


34/45

burn. Resistors in electronic circuits are typicaly rated 1/8W,

1/4W, and 1/2W. 1/8W is almost always used in signal circuit

applications. When powering a l ight emitting diode, a

comparatively large current flows through the resistor, so you

need to consider the power rating of the resistor you choose.

6.1 Rating electric power

For example, to power a 5V circuit using a 12V supply, a three-

terminal voltage regulator is usually used. However, if you try todrop the voltage from 12V to 5V using only a resistor, then you

need to calculate the power rating of the resistor as well as the

resistance value. At this time, the current consumed by the 5V

circuit needs to be known. Here are a few ways to find out how

much current the circuit demands. Assemble the circuit and

measure the actual current used with a multi-meter. Check the

component's current use against a standard table. Assume the

current consumed is 100 mA (mill iamps) in the following

example. 7V must be dropped with the resistor. The resistance

value of the resistor becomes 7V / 0.1A = 70(ohm). The

consumption of electric power for this resistor becomes 0.1A x

0.1A x 70 ohm = 0.7W. Generally, it's safe to choose a resistor

which has a power rating of about twice the power consumption

needed.

34


35/45

6.2 Resistance value

As for the standard resistance value, the values used can be

divided like a logarithm. For example, in the case of E3, The

values [1], [2.2], [4.7] and [10] are used. They divide 10 into

three, like a logarithm. In the case of E6 : [1], [1.5], [2.2], [3.3],

[4.7], [6.8], [10]. In the case of E12 : [1], [1.2], [1.5], [1.8], [2.2],

[2.7], [3.3], [3.9], [4.7], [5.6], [6.8], [8.2], [10]. It is because of

this that the resistance value is seen at a glance to be a discrete

value. The resistance value is displayed using the color code

( the colored bars/the colored stripes ), because the average

resistor is too small to have the value printed on it with numbers.

You had better learn the color code, because almost all resistors

of 1/2W or less use the color code to display the resistance

value.

6.3 Fixed Resistors

A fixed resistor is one in which the value of its resistance cannot

change.

6.4 Carbon film resistors

This is the most general purpose, cheap resistor. Usually the

tolerance of the resistance value is 5%. Power ratings of 1/8W,

1/4W and 1/2W are frequently used. Carbon film resistors have

a disadvantage; they tend to be electrically noisy. Metal film

35
http://www.interq.or.jp/japan/se-inoue/e_resistor.htm#colorcodehttp://www.interq.or.jp/japan/se-inoue/e_resistor.htm#colorcode


36/45

resistors are recommended for use in analog circuits. However, I

have never experienced any problems with this noise. The

physical size of the different resistors are as follows.

This resistor is called a Single-In-Line(SIL) resistor network. It is

made with many resistors of the same value, all in one package.

One side of each resistor is connected with one side of all the

other resistors inside. One example of its use would be to

control the current in a circuit powering many light emitting

diodes (LEDs). In the photograph on the left, 8 resistors are

housed in the package. Each of the leads on the package is one

resistor. The ninth lead on the left side is the common lead. The

face value of the resistance is printed. ( It depends on the

supplier. ) Some resistor networks have a "4S" printed on the

top of the resistor network. The 4S indicates that the package

contains 4 independent resistors that are not wired together

inside. The housing has eight leads instead of nine. The internal

wiring of these typical resistor networks has been illustrated

below. The size (black part) of the resistor network which I have

36


37/45

is as follows: For the type with 9 leads, the thickness is 1.8 mm,

the height 5mm, and the width 23 mm. For the types with 8

component leads, the thickness is 1.8 mm, the height 5 mm, and

the width 20 mm.

6.5 Variable Resistors

There are two general ways in which variable resistors are used.

One is the variable resistor which value is easily changed, like

the volume adjustment of Radio. The other is semi-fixed resistor

that is not meant to be adjusted by anyone but a technician. It is

used to adjust the operating condition of the circuit by the

technician. Semi-fixed resistors are used to compensate for the

inaccuracies of the resistors, and to fine-tune a circuit. The

rotation angle of the variable resistor is usually about 300

degrees. Some variable resistors must be turned many times to

37


38/45

use the whole range of resistance they offer. This allows for very

precise adjustments of their value. These are called

"Potentiometers" or "Trimmer Potentiometers."

In the photograph to the left, the variable resistor typically used

for volume controls can be seen on the far right. Its value is very

easy to adjust. The four resistors at the center of the photograph

are the semi-fixed type. These ones are mounted on the printed

circuit board. The two resistors on the left are the trimmer

potentiometers.

This symbol is used to indicate a variable resistor in a circuit

diagram. There are three ways in which a variable resistor's

value can change according to the rotation angle of its axis.

When type "A" rotates clockwise, at first, the resistance value

changes slowly and then in the second half of its axis, it

changes very quickly. The "A" type variable resistor is typically

used for the volume control of a radio, for example. It is well

suited to adjust a low sound subtly. It suits the characteristics of

38


39/45

the ear. The ear hears low sound changes well, but isn't as

sensitive to small changes in loud sounds. A larger change is

needed as the volume is increased. These "A" type variable

resistors are sometimes called "audio taper" potentiometers. As

for type "B", the rotation of the axis and the change of the

resistance value are directly related. The rate of change is the

same, or linear, throughout the sweep of the axis. This type

suits a resistance value adjustment in a circuit, a balance circuit

and so on. They are sometimes called "linear taper"

potentiometers. Type "C" changes exactly the opposite way to

type "A". In the early stages of the rotation of the axis, the

resistance value changes rapidly, and in the second half, the

change occurs more slowly. This type isn't too much used. It is a

special use. As for the variable resistor, most are type "A" or

type "B".

39


40/45

7. Soldering

The soldering is the basic work for electronic circuit engineering.

I will introduce the tools for soldering below. The sufficient

attention is necessary during work, because soldering handles a

high temperature. Pay attention to the handling of the soldering

iron sufficiently, because it becomes burn, fire more, carelessly.

7.1 Soldering iron

Soldering iron is a necessary instrument when you solder.

Solder is hardening in a normal temperature, but solder can melt

easily by using the soldering iron and the parts and wiring

materials can be fixed to the printed wiring board(PWB).The

important point is temperature of the soldering iron. For

soldering, it needs to become the temperature of the

object(PWB, parts, wire etc) to solder melting temperature.

However, the temperature of soldering iron must not be too high.

The electronic component gets damage with high temperature.

So, you need to solder in a short time. Sometimes, the loose

contact of soldering occurs. It is difficult to confirm only by

looking at. When the temperature of the object is not enough,

the loose contact will be occured. At the end of assembling of

40


41/45

the electronic circuit, you need to check the soldered contact

with circuit tester etc.

7.2 Electric power

There are various kind of soldering irons. I am using 3 kinds of

soldering irons. 25W type, 80W type, 15W type

7.3 The tip of iron

The soldering is done at the tip of iron. So, the tip of iron is very

important. There is the type that the tip of soldering iron is made

of copper stick. But I don't recommend that type. Because, the

copper stick rusts easily by heat and it becomes difficult to

convey heat. Also the tip of copper stick melts with solder. It

becomes difficult to solder. I recommend the one that is difficult

to convey heat. There are many shape of tips. The tip which fit

to the DIP type IC is used to remove the ICs. All of the solder on

the pins can be melt at same time then it easy to remove the IC.I

do not have such kind of soldering iron.

41


42/45

Usually the soldering iron is heated by electricity. However,

there is the soldering iron heated by gas. It is convenient to

carry.

7.4 Soldering iron stand

The soldering iron becomes high temperature. Therefore it can't

be placed on the desk directly. The stabilized soldering iron

stand is necessary. When making the electronic circuit,

sometime I forgot the existence of soldering iron, because I

have devoted to the parts, wiring etc. It was serious when I

noticed, desk was burning. You need to choose the iron stand

with appropriate weight which can hold iron stably. Also you

need to choose the iron stand that fit the form of iron. Usually I

wipe the tip of iron with moistened sponge. Therefore I use the

iron stand with the place for sponge. This is your taste.

7.5 Solder

42


43/45

The solder is the alloy of lead and tin. As for good solder, the

containment rate of t in is high. The finish of soldering is

beautiful. The price is a little bit high. There are several kinds of

solder, solder wire( thread form solder ) is convenient for

electronic circuit making. This solder wire is doing the structure

of the pipe and flux is included inside. Flux melts together with

the solder and the solder becomes easy to attach to the

component leads. There are some thicknesses of solder wire. I

am usually using the one that diameter is 0.5 mm. The

containment rate of the tin is 60%.

7.6 Solder sucker

The failure of soldering occurs often. In this case, the part or the

wiring must be removed. I will introduce the instruments that can

be used for desoldering

7.7 Solder pump

This is the tool that can be absorbed the melted solder with the

repulsion power of the spring that was built in with the principle

of the piston. The usage is shown below. Push down the knob of

the upper part of the pump against to spring until it is locked.

Melt the solder of the part that wants to absorb solder with iron.

Apply the nozzle of the pump to the melted solder part. Push the

release knob of pump. Then the plunger of the pump is pushed

43


44/45

up with the power of spring and solder is absorbed inside the

pump. You need to do this operation quickly, otherwise the part

gets damage by the heat. A little practice is needed.

7.8 De-soldering wireThis is made of thin copper net wire like a screen cable in a

coaxial cable. Like water inhales to cloth, the solder is absorbed

to the net wire by a capillary tube phenomenon. The usage is

shown below. Apply the de-soldering wire to the part that wants

to take solder. Apply the soldering iron from the top and Melt the

solder. The melted solder is absorbed to de-soldering wire witha capillary tube phenomenon. At this time you absorb solder

while shifting de-soldering wire. When the solder can not be

removed in the once, remove repeatedly while shifting the de-

soldering wire. There are several kinds of width of de-soldering

wire. I am using the one with 2mm width.

44


45/45

Documents

History of CDMA