resistor

Basically all the material has a resistive nature, but some materials such as copper, silver, gold and metal materials generally have very little resistance. The material is well deliver an electric current, so called a conductor. The opposite of a conductive material, ie material such as rubber, glass, carbon has a greater resistance to withstand the flow of electrons so it is referred to as an insulator.
Resistors are the basic components of electronics are always used in every electronic circuit that can function as a regulator or to limit the amount of current flowing in a circuit. With a resistor, electrical current can be distributed according to need. As the name implies is resistive resistor and is generally made of carbon materials. Unit resistance of a resistor is called Ohm or represented by the symbol Ω (Omega).
In the electronic circuit, resistors are denoted with the letter "R". Judging from the material, there are several types of resistors in the market include: Carbon Resistor, wirewound, and Metalfilm. There is also a resistor that can be changed resistance value, among others: Potentiometer, Rheostat and Trimmer (trimpot). There was also a resistor that changes its resistance when exposed to light called LDR (Light Dependent Resistor) and resistor resistance value will increase in size when exposed to hot temperatures whose name PTC (Positive Thermal Coefficient) resistor and a small resistance value will increase when exposed to temperatures whose names are hot NTC (Negative Thermal Coefficient).
For the types of carbon resistors and metalfilm typically used color codes to guide the value of resistance (resistance) of the resistor. This resistor has a shape like a tube with two legs on the left and right. In the body there is a circle form a ring color code, the code is great to know without having to measure the magnitude of the resistance with ohmmeter. The color code is the manufacturing standards issued by EIA (Electronic Industries Association) as shown in Table 1.1.

Table 1.1 The color of the ring resistor

Scale resistance of a resistor is read from the most forward position of the ring toward the tolerance ring. Usually the tolerance ring is in position on the resistor body that most corner or even with the width of the more prominent, while the position of the first ring is a bit inward. Thus the user is immediately aware of how much tolerance resistor. If we have been able to determine where the first ring next is to read the resistance value.
Number of rings which are generally circular in accordance with a large resistor tolerance. Usually the resistor with a tolerance of 5%, 10% or 20% have 3 rings (not including the tolerance ring). But the resistor with a tolerance of 1% or 2% (small tolerance) has 4 rings (not including the tolerance ring). The first ring and so on successively demonstrated great value unit, and the last ring is pengalinya factor.
For example a resistor with a ring of yellow, violet, red and gold. Gold-colored ring is the ring of tolerance. Thus the ring resistor color sequence is, the first ring of yellow, violet colored and the second ring to the three red rings. Ring to a four-colored gold is a tolerance ring. From table 1.1 note if golden ring of tolerance, it means that this resistor has a tolerance of 5%. Resistance value calculated in accordance with the order of the color. The first is to determine the unit value of this resistor. Since this resistor resistor 5% (which usually has three rings in addition to tolerance rings), then the value of the units is determined by the first ring and second ring. Still from Table 1.1, note the yellow ring and ring value = 4 value = violet 7. So the first and second rings or yellow and violet respectively, the unit is 47. The third ring is a multiplier, and if the color red ring means pengalinya factor is 100. So with this known resistor value is the value x multiplier units or 47 x 100 = 4700 K Ohm = 4.7 Ohm (in electronic circuits are usually written 4k7 Ohm) and the tolerance is + 5%. The meaning of tolerance itself is a restriction of minimum and maximum resistance value which is owned by the resistor. So the true value of 4.7 k Ohm resistor + 5% is:
4700 x 5% = 235
Thus,
Rmaksimum = 4700 + 235 = 4935 Ohm
Rminimum = 4700 - 235 = 4465 Ohm
If the resistor on the measure using an ohmmeter and its value in the range of maximum and minimum value (4465 s / d 4935), the resistor was still meet the standards. The value of tolerance is provided by the manufacturer of resistors to anticipate the characteristics of a material that is not the same between one resistor with another resistor so that the electronics designers can estimate the tolerance factor in their design. The smaller the tolerance value, the better the quality of the resistor. So that the market value of tolerance resistors have 1% (eg resistors metalfilm) is much more expensive than resistors having tolerances of 5% (carbon resistor)
Other specifications to consider in choosing a resistor on a draft of the resistance is greater than his or watts maximum power that is able to hold the resistor. Because the resistors in aliri working with electric current, there will be a power dissipation of heat for: 

 

The greater the physical size of a resistor, may indicate the greater ability of the resistor power dissipation. Generally available in the market size of 1 / 8, 1 / 4, 1 / 2, 1, 2, 5, 10 and 20 watts. Resistor which has a maximum power dissipation of 5, 10 and 20 watts are generally elongated rectangular-shaped beam of white, but some are cylindrical and are usually for large size of this resistor the resistance value in the direct print dibadannya shaped rings are not color, for example 100Ω5W or 1KΩ10W.

Judging from its function, the resistor can be divided into:

    * Fixed Resistors (Fixed Resistors)
That resistor whose value can not be changed, so it always remains (constant). This resistor usually made from nikelin or carbon. Serves as a voltage divider, regulate or limit the current in a circuit as well as enlarging and reducing stress.

    * Not Fixed Resistor (variable resistor)
That is the resistor whose value can change by shifting or rotating the toggle on the tool, so that the resistor value can be set according to need. Functioning as a volume control (adjust the size of the current), tone control on the sound system, high and low tone control (bass / treble) and serves as a voltage divider current and voltage.

    * NTC and PTC resistors.
NTC (Negative Temperature Coefficient), a resistor whose value will grow smaller when exposed to hot temperatures. While the PTC (Positive Temperature Coefficient), the resistor whose value will be greater when the temperature cools.

    * Resistor LDR
LDR (Light Dependent Resistor) are the type of resistor that changes its resistance due to the influence of light. When exposed to black light the greater the value of his prisoner, when exposed to bright light while the value becomes smaller.

    * The series of resistors
In practice, the designers sometimes need a resistor with a certain value. However, the resistor values ​​are not in the shop, even the factory itself does not produce it. Solution to get a resistor with resistance values ​​that can be done uniquely by assembling several resistors so we get the required resistance value. There are two ways to couple the resistor, namely:
1. Serial Method
2. Parallel Method
The series of resistors in series will result in larger total resistance value. Below is an example of resistors arranged in series.

 Series resistor in the circuit applies the formula: 

While the series of resistors in parallel will result in a replacement value of the smaller resistance. Below are examples of resistors arranged in parallel

In a parallel resistor circuit applies the formula: 

3. Standard resistor values
Not all resistance values ​​are available on the market. Table 1.2 is an example table standard resistor value in the market. Data on the resistors on the market can be obtained from the Data Sheet issued by the manufacturer of resistors.

Below are some formulas (Ohm's Law) which is often used in the calculation of electronics: 

Where:
V = voltage measured in Volts
I = current measured in amperes
R = resistance measured in Ohms
P = power measured in Watts
Conversion unit:
1 Ohm = 1 Ω
1 K Ohm = 1 K Ω
1 M Ohm = 1 M Ω
1 K Ω = 1.000 Ω
1 M Ω Ω = 1,000 K
1 M Ω = 1,000,000 Ω
(M = Mega (106); K = Kilo (103)

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Colpitts Oscillator at Resonance

Using a circuit from the RF schematics section, and the formula from the theory section, you can estimate the resonant frequency for this oscillator:

Working out the parallel capacitance, C1 C2, (27*27)/(27+27) = 13.5pF
Assuming that the coil, L has an inductance of 0.2uH then:

 

= 96.8 MHz

This puts the frequency of oscillation in the middle of the UK FM Band (87.5 - 108 MHz). If an inductor with a core is used, then the oscillator can be tuned by moving the core. If an air spaced core is used, then tuning is achieved by physically squeezing or separating the turns.

semiconductor

Basic Principles

Semiconductors are the basic elements of electronics components such as diodes, transistors and an IC (integrated circuit). Called semi-or half-conductors, since this material is not a pure conductor. Metals such as copper, iron, tin referred to as a good conductor because the metal has an atomic arrangement is such that electrons can move freely. 

Atomic Structure of Semiconductors

Semiconductor materials are widely known example is Silicon (Si), Germanium (Ge) and Gallium arsenide (GaAs). Germanium is a material previously only known for making semiconductor components. But lately, silicon became popular after it was discovered how to extract these materials from nature. Silicon is the second largest material on earth after oxygen (O2). Sand, glass and other stones are natural materials that contain many elements of silicon. Can you calculate the amount of sand on the beach.
Crystalline structure of silicon atoms, one atom core (nucleus) each have 4 valence electrons. Nuclei are stable bond is when surrounded by 8 electrons, so the 4 pieces of crystal atomic electrons form a covalent bond with neighboring atomic ions. At very low temperatures (0oK), the atomic structure of silicon visualized as shown below.

two-dimensional structure of crystalline silicon
 

Covalent bond causes the electrons can not move from one nucleus to another nucleus. In such conditions, semiconductor materials are insulators because the electrons can not move to conduct electricity. At room temperature, there are some covalent bonds are loose due to heat energy, thus allowing the electrons released from this bond. However, only some small amount that can be detached, so it is not possible to be a good conductor.
Physicists, especially the control of quantum physics at that time was trying to give this doping in semiconductor materials. The provision is intended to get a doping-free valence electrons in much smaller lots and permanent, which will hopefully be able to conduct electricity. In fact such, they are fun once and a genius.

Type-N

For example on a silicon material given doping phosphorus or arsenic pentavalen the crystalline material with atomic nuclei has 5 valence electrons. With doping, silicon is no longer pure (impurity semiconductor) will have an excess of electrons. Excess electrons to form n-type semiconductors. N-type semiconductor is also called a donor ready to release electrons.

doping atoms pentavalen
 

Type-P

If silicon were doped Boron, Gallium or Indium, it will be obtained p-type semiconductor. To obtain p-type silicon, the material is a material dopingnya with trivalent ions of elements which has 3 electrons in the valence band. Since the silicon ion has 4 electrons, thus there is a covalent bond is perforated (holes). Hole is described as an electron acceptor that is ready to accept. Thus, a deficiency of electrons cause the semiconductor is a p-type.

trivalent atom doping 

Resistance

P-type semiconductor or n-type by itself is nothing but a resistor. Just like carbon resistors, semiconductors having resistance. This method is used to create a resistor in a semiconductor component. However a large minor resistance that can be obtained because of limited volume of the semiconductor itself.

PN diode

If the two types of semiconductor material is attached - use glue probably yes:), then the connection will be obtained PN (pn junction) is known as a diode. In the type material of manufacture is P and N type is not connected to harpiah, but from one material (monolithic) to give doping (impurity material) is different. 

p-n connection 

If given a forward voltage (forward bias), where P side voltage is greater than the N, electrons can easily flow from the N side to fill the void of electrons (holes) in the P.

forward bias 

Conversely, if given a reverse voltage (reverse bias), understood that no electrons can flow from the N side of the fill hole on the side of P, because the voltage potential on the N side is higher.
Diode will only be able to stream flow in one direction only, so it is used for applications rectifier circuit (rectifier). Diode, Zener, LED, varactor and varistor are some connections PN semiconductor components are discussed in a special column. 

Bipolar Transistor

The transistor is a diode with two connections (junction). Connections that form the PNP and NPN transistor. The ends of the terminal in a row are called emitter, base and collector. Base is always in the middle, between the emitter and collector. These transistors are called bipolar transistor, because the structure and working principle of the displacement of electrons depends on the negative pole to fill shortage of electrons (holes) in the positive pole. bi = 2 and polar = pole. William Schockley in 1951 who first discovered bipolar transistors.

NPN and PNP transistors 

Will be explained later, the transistor is a component that works as a switch (switch on / off) and also as an amplifier (amplifier). Bipolar transistor is the innovation that replaces the transistor tubes (vacuum tube). In addition to the bipolar transistor dimensions are relatively smaller, power dissipation is also smaller so it can work in colder temperatures. In some applications, transistor tubes are still used primarily in audio applications, to get good sound quality, but power consumption is very large. For to be able to release electrons, the technique used is as in the heating filament incandescent lamp.

DC Bias

Junction bipolar transistor has a second that can be equated with the incorporation of 2 pieces of diodes. Emitter-Base is a base-collector junction and other junctions. As in the diode, current will only flow only if given a positive bias, ie only if the voltage on the material P is more positive than the material N (forward bias). In the following illustration NPN transistor, the base-emitter junction are positively biased while the base-collector gets a negative bias (reverse bias).

Electron current NPN transistor 

Because the base-emitter got it as a positive bias on the diode, electrons flow from emitter to base. Collectors in this series is more positive because it gets a positive voltage. Because the collector is more positive, the flow of electrons moving toward this pole. For example there is no collector, the flow of electrons will be entirely toward the base as in the diode. But because the base width is very thin, only a portion of electrons that can be joined with the existing holes on the base. Most will penetrate the base layer toward the collector. This is why if the two diodes can not be combined into a transistor, because the requirements are that the width of the base must be very thin so it can be hit by electrons.
If for example the base-emitter voltage is reversed (reverse bias), then it will not happen the flow of electrons from the emitter to the collector. If gently 'tap' given base forward bias (forward bias), electrons flow towards the collector and the magnitude of the bias current is proportional to the given base. In other words, adjust the amount of base current of electrons flowing from emitter to collector. This is called the strengthening effect transistors, because of the small base currents produce emitter-collector current is greater. The term amplifier (reinforcement) to be misguided, because with the above explanation is actually occurring is not strengthening, but a smaller flow control a larger current flow. Can also be explained that the base set to open and close the emitter-collector current flow (switch on / off).
In the PNP transistors, the same phenomenon can be explained by giving a bias as shown below. In this case the so-called displacement current is the flow hole.

Hole current PNP transistors
 

To facilitate discussion of the principle of further bias transistor, the transistor parameters of the following is the terminology. In this case the current direction of the potential is greater to a smaller potential.

potential flow

IC: collector current
IB: base flow
IE: the emitter currents
VC: voltage collector
VB: base voltage
VE: emitter voltage
VCC: voltage at the collector
VCE: collector-emitter voltage clamp
VEE: the voltage on the emitter
VBE: base-emitter voltage clamp
ICBO: current base-collector
VCB: collector-base voltage clamp
Please note, although no difference in the doping material for the emitter and collector, but in practice the emitter and collector can not be reversed.

cross section of a bipolar transistor 

From a silicon material (monolithic), the emitter is made first, then base with different doping and the last is the collector. Sometimes also the effect of diodes made on the terminals so that the flow will only occur in the desired direction.

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ELECTRONIC SYMBOLS

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POWER SUPPLY SCHEME

 

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BJT

BJT (Bipolar Junction Transistor)

While the C-B (common-base) amplifier is known for wider bandwidth than the C-E (common-emitter) configuration, the low input impedance (10s of Ω) of C-B is a limitation for many applications. The solution is to precede the C-B stage by a low gain C-E stage which has moderately high input impedance (kΩs). See Figure below. The stages are in a cascode configuration, stacked in series, as opposed to cascaded for a standard amplifier chain. See “Capacitor coupled three stage common-emitter amplifier” Capacitor coupled for a cascade example. The cascode amplifier configuration has both wide bandwidth and a moderately high input impedance.

The cascode amplifier is combined common-emitter and common-base. This is an AC circuit equivalent with batteries and capacitors replaced by short circuits.

The key to understanding the wide bandwidth of the cascode configuration is the Miller effect Miller effect. It is the multiplication of the bandwidth robbing collector-base capacitance by beta. This C-B capacitance is smaller than the E-B capacitance. Thus, one would think that the C-B capacitance would have little effect. However, in the C-E configuration, the collector output signal is out of phase with the input at the base. The collector signal capacitively coupled back opposes the base signal. Moreover, the collector feedback is beta times larger than the base signal. Thus, the small C-B capacitance appears beta times larger than its actual value. This capacitive gain reducing feedback increases with frequency, reducing the high frequency response of a C-E amplifier.

A common-base configuration is not subject to the Miller effect because the grounded base shields the collector signal from being fed back to the emitter input. Thus, a C-B amplifier has better high frequency response. To have a moderately high input impedance, the C-E stage is still desirable. The key is to reduce the gain (to about 1) of the C-E stage to reduce the Miller effect C-B feedback to 1·C_CB. The total C-B feedback is the Miller capacitance 1·C_CB plus the actual capacitance C_CB for a total of 2·C_CB. This is a considerable reduction from β·C_CB.

The way to reduce the common-emitter gain is to reduce the load resistance. The gain of a C-E amplifier is approximately R_C/R_E. The internal emitter resistance R_EE at 1mA emitter current is 26Ω. For details on the 26Ω, see “Derivation of R_EE”, see REE. The collector load R_C is the resistance of the emitter of the C-B stage loading the C-E stage, 26Ω again. CE gain amplifier gain is approximately R_C/R_E=26/26=1. We now have a moderately high input impedance C-E stage without suffering the Miller effect, but no dB voltage gain. The C-B stage provides a high voltage gain. Thus, the cascode has moderately high input impedance of the CE, good gain, and good bandwidth of the C-B.

SPICE: Cascode and common-emitter for comparison.

The SPICE version of both a cascode amplifier, and for comparison, a common-emitter amplifier is shown in Figure above. The netlist is in Table below. The AC source V3 drives both amplifiers via node 4. The bias resistors for this circuit are calculated in an example problem cascode.

SPICE waveforms. Note that Input is multiplied by 10 for visibility.

SPICE netlist for printing AC input and output voltages.

*SPICE circuit <03502.eps> from XCircuit v3.20
V1 19 0 10
Q1 13 15 0 q2n2222
Q2 3 2 A q2n2222
R1 19 13 4.7k
V2 16 0 1.5
C1 4 15 10n
R2 15 16 80k
Q3 A 5 0 q2n2222
V3 4 6 SIN(0 0.1 1k)  ac 1
R3 1 2 80k
R4 3 9 4.7k
C2 2 0 10n
C3 4 5 10n
R5 5 6 80k
V4 1 0 11.5
V5 9 0 20
V6 6 0 1.5
.model q2n2222 npn (is=19f bf=150
+ vaf=100 ikf=0.18 ise=50p ne=2.5 br=7.5
+ var=6.4 ikr=12m isc=8.7p nc=1.2 rb=50
+ re=0.4 rc=0.3 cje=26p tf=0.5n
+ cjc=11p tr=7n xtb=1.5 kf=0.032f af=1)
.tran 1u 5m
.AC DEC 10 1k 100Meg
.end

The waveforms in Figure above show the operation of the cascode stage. The input signal is displayed multiplied by 10 so that it may be shown with the outputs. Note that both the Cascode, Common-emitter, and Va (intermediate point) outputs are inverted from the input. Both the Cascode and Common emitter have large amplitude outputs. The Va point has a DC level of about 10V, about half way between 20V and ground. The signal is larger than can be accounted for by a C-E gain of 1, It is three times larger than expected.

Cascode vs common-emitter banwidth.

Figure above shows the frequency response to both the cascode and common-emitter amplifiers. The SPICE statements responsible for the AC analysis, extracted from the listing:

V3 4 6 SIN(0 0.1 1k)  ac 1
.AC DEC 10 1k 100Meg

Note the “ac 1” is necessary at the end of the V3 statement. The cascode has marginally better mid-band gain. However, we are primarily looking for the bandwidth measured at the -3dB points, down from the midband gain for each amplifier. This is shown by the vertical solid lines in Figure above. It is also possible to print the data of interest from nutmeg to the screen, the SPICE graphical viewer (command, first line):

nutmeg 6 -> print frequency db(vm(3)) db(vm(13))

Index   frequency     db(vm(3))  db(vm(13)) 
22      0.158MHz      47.54      45.41
33      1.995MHz      46.95      42.06
37      5.012MHz      44.63      36.17

Index 22 gives the midband dB gain for Cascode vm(3)=47.5dB and Common-emitter vm(13)=45.4dB. Out of many printed lines, Index 33 was the closest to being 3dB down from 45.4dB at 42.0dB for the Common-emitter circuit. The corresponding Index 33 frequency is approximately 2Mhz, the common-emitter bandwidth. Index 37 vm(3)=44.6db is approximately 3db down from 47.5db. The corresponding Index37 frequency is 5Mhz, the cascode bandwidth. Thus, the cascode amplifier has a wider bandwidth. We are not concerned with the low frequency degradation of gain. It is due to the capacitors, which could be remedied with larger ones.

The 5MHz bandwith of our cascode example, while better than the common-emitter example, is not exemplary for an RF (radio frequency) amplifier. A pair of RF or microwave transistors with lower interelectrode capacitances should be used for higher bandwidth. Before the invention of the RF dual gate MOSFET, the BJT cascode amplifier could have been found in UHF (ultra high frequency) TV tuners.

• REVIEW
• A cascode amplifier consists of a common-emitter stage loaded by the emitter of a common-base stage.
• The heavily loaded C-E stage has a low gain of 1, overcoming the Miller effect
.
• A cascode amplifier has a high gain, moderately high input impedance, a high output impedance, and a high bandwidth.