Basics Of Electronics and Communication and VLSI

Basics Of Electronics and Communication and VLSI 

Electronics = Electron  +   tronics  => Elctrons Theory  =>  Momentum of Electron  => drive the Electron from point to point.

Basics  of Electronics

Electronics is the science of how to control electric energy, energy in which the electrons have a fundamental role. Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive electrical components and interconnection technologies. Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements; such a circuit is described as an electronic circuit.

Vacuum tubes

Transistors

Diodes

Integrated Circuits

Vacuum Tubes

Diode

 Basic Diode with Color Line is cathode and opposite anode

In the Diode tutorials we saw that simple diodes are made up from two pieces of semiconductor material, either silicon or germanium to form a simple PN-junction and we also learnt about their properties and characteristics. If we now join together two individual signal diodes back-to-back, this will give us two PN-junctions connected together in series that share a common P or N terminal. The fusion of these two diodes produces a three layer, two junction, three terminal device forming the basis of a Bipolar Junction Transistor, or BJTfor short.

Transistor:

1. A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit.
2. 
   

   Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. The transistor’s ability to change between these two states enables it to have two basic functions: “switching” (digital electronics) or “amplification” (analogue electronics). Then Bipolar Transistors have the ability to operate within three different regions:

   
   

   • • Active Region   –   the transistor operates as an amplifier and Ic = β.Ib
   • • Saturation   –   the transistor is “Fully-ON” operating as a switch and Ic = I(saturation)
   • • Cut-off   –   the transistor is “Fully-OFF” operating as a switch and Ic = 0

Transistors can be regarded as a type of switch, as can many electronic components. They are used in a variety of circuits and you will find that it is rare that a circuit built in a school Technology Department does not contain at least one transistor. They are central to electronics and there are two main types; NPN and PNP. Most circuits tend to use NPN. There are hundreds of transistors which work at different voltages but all of them fall into these two categories.

Bipolar Transistor Construction

Bipolar Transistor Configurations

As the Bipolar Transistor is a three terminal device, there are basically three possible ways to connect it within an electronic circuit with one terminal being common to both the input and output. Each method of connection responding differently to its input signal within a circuit as the static characteristics of the transistor vary with each circuit arrangement.

• • Common Base Configuration   –   has Voltage Gain but no Current Gain.
• • Common Emitter Configuration   –   has both Current and Voltage Gain.
• • Common Collector Configuration   –   has Current Gain but no Voltage Gain.

The Common Base (CB) Configuration

As its name suggests, in the Common Base or grounded base configuration, the BASE connection is common to both the input signal AND the output signal with the input signal being applied between the base and the emitter terminals. The corresponding output signal is taken from between the base and the collector terminals as shown with the base terminal grounded or connected to a fixed reference voltage point.

The input current flowing into the emitter is quite large as its the sum of both the base current and collector current respectively therefore, the collector current output is less than the emitter current input resulting in a current gain for this type of circuit of “1” (unity) or less, in other words the common base configuration “attenuates” the input signal.

The Common Base Transistor Circuit

This type of amplifier configuration is a non-inverting voltage amplifier circuit, in that the signal voltages Vin and Vout are “in-phase”. This type of transistor arrangement is not very common due to its unusually high voltage gain characteristics. Its output characteristics represent that of a forward biased diode while the input characteristics represent that of an illuminated photo-diode.

Also this type of bipolar transistor configuration has a high ratio of output to input resistance or more importantly “load” resistance ( RL ) to “input” resistance ( Rin ) giving it a value of “Resistance Gain”. Then the voltage gain ( Av ) for a common base configuration is therefore given as:

Common Base Voltage Gain

Where: Ic/Ie is the current gain, alpha ( α ) and RL/Rin is the resistance gain.

The common base circuit is generally only used in single stage amplifier circuits such as microphone pre-amplifier or radio frequency ( Rf ) amplifiers due to its very good high frequency response.

The Common Emitter (CE) Configuration

In the Common Emitter or grounded emitter configuration, the input signal is applied between the base, while the output is taken from between the collector and the emitter as shown. This type of configuration is the most commonly used circuit for transistor based amplifiers and which represents the “normal” method of bipolar transistor connection.

The common emitter amplifier configuration produces the highest current and power gain of all the three bipolar transistor configurations. This is mainly because the input impedance is LOW as it is connected to a forward biased PN-junction, while the output impedance is HIGH as it is taken from a reverse biased PN-junction.

The Common Emitter Amplifier Circuit

In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing into the transistor as the emitter current is given as Ie = Ic + Ib.

The Junction Transistor A bipolar junction transistor consists of three regions of dopedsemiconductors. A small current in the center or base region can be used to control a larger currentflowing between the end regions (emitter and collector). The device can be characterized as acurrent amplifier, having many applications foramplification andswitching. Constraints on operation Transistor operating conditions Varieties of Transistors Details about conduction in transistors Determining collector current Details about base-emitter junction

Index Semiconductor concepts Semiconductors for electronics Electronics concepts

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Transistor as Current Amplifier The larger collector current IC is proportional to the base current IB according to the relationship IC =βIB , or more precisely it is proportional to the base-emitter voltage VBE . The smaller base current controls the larger collector current, achieving current amplification. The analogy to a valve is sometimes helpful. The smaller current in the base acts as a "valve", controlling the larger current from collector to emitter. A "signal" in the form of a variation in the base current is reproduced as a larger variation in the collector-to-emitter current, achieving an amplification of that signal. Constraints on operation Comments on structure To pnp version

Index Semiconductor concepts Semiconductors for electronics Electronics concepts Reference Diefenderfer /Holton p156

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Transistor Structure The junction transistor Current amplifier operation Constraints on operation	Index Semiconductor concepts Semiconductors for electronics Electronics concepts
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Transistor as Current Amplifier The larger collector current IC is proportional to the base current IB according to the relationship IC =βIB , or more precisely it is proportional to the base-emitter voltage VBE . The smaller base current controls the larger collector current, achieving current amplification. Constraints on operation To npn version	Index Semiconductor concepts Semiconductors for electronics Electronics concepts
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Constraints on Transistor Operation The bold text and the "buttons" are active links to further details.	Index Semiconductor concepts Semiconductors for electronics Electronics concepts
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Transistor Maximum Values Part of the manufacturer's data for transistors is a set of maximum values which must not be exceeded in its operation. These form some of the constraints on transistor operation which are a part of the design of any circuit. A typical set, for the silicon transistor 2N2222: Collector-Base Voltage = 60 v Collector-Emitter Voltage = 30 v Base-Emitter Voltage = 5 v Power dissipation = 500 mW Temperature 125 C

Index Semiconductor concepts Semiconductors for electronics Electronics concepts

How a junction transistor works

How a field-effect transistor (FET) works

All transistors work by controlling the movement of electrons, but not all of them do it the same way. Like a junction transistor, a FET (field effect transistor) has three different terminals—but they have the names source (analogous to the emitter), drain (analogous to the collector), and gate (analogous to the base). In a FET, the layers of n-type and p-type silicon are arranged in a slightly different way and coated with layers of metal and oxide. That gives us a device called a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

Although there are extra electrons in the n-type source and drain, they cannot flow from one to the other because of the holes in the p-type gate in between them. However, if we attach a positive voltage to the gate, an electric field is created there that allows electrons to flow in a thin channel from the source to the drain. This "field effect" allows a current to flow and switches the transistor on:

For the sake of completeness, we could note that a MOSFET is a unipolar transistor because only one kind ("polarity") of electric charge is involved in making it work

The Common Base (CB) Configuration

As its name suggests, in the Common Base or grounded base configuration, the BASE connection is common to both the input signal AND the output signal with the input signal being applied between the base and the emitter terminals. The corresponding output signal is taken from between the base and the collector terminals as shown with the base terminal grounded or connected to a fixed reference voltage point.

The input current flowing into the emitter is quite large as its the sum of both the base current and collector current respectively therefore, the collector current output is less than the emitter current input resulting in a current gain for this type of circuit of “1” (unity) or less, in other words the common base configuration “attenuates” the input signal.

The Common Base Transistor Circuit

This type of amplifier configuration is a non-inverting voltage amplifier circuit, in that the signal voltages Vin and Vout are “in-phase”. This type of transistor arrangement is not very common due to its unusually high voltage gain characteristics. Its output characteristics represent that of a forward biased diode while the input characteristics represent that of an illuminated photo-diode.

Also this type of bipolar transistor configuration has a high ratio of output to input resistance or more importantly “load” resistance ( RL ) to “input” resistance ( Rin ) giving it a value of “Resistance Gain”. Then the voltage gain ( Av ) for a common base configuration is therefore given as:

Common Base Voltage Gain

Where: Ic/Ie is the current gain, alpha ( α ) and RL/Rin is the resistance gain.

The common base circuit is generally only used in single stage amplifier circuits such as microphone pre-amplifier or radio frequency ( Rf ) amplifiers due to its very good high frequency response.

The Common Emitter (CE) Configuration

In the Common Emitter or grounded emitter configuration, the input signal is applied between the base, while the output is taken from between the collector and the emitter as shown. This type of configuration is the most commonly used circuit for transistor based amplifiers and which represents the “normal” method of bipolar transistor connection.

The common emitter amplifier configuration produces the highest current and power gain of all the three bipolar transistor configurations. This is mainly because the input impedance is LOW as it is connected to a forward biased PN-junction, while the output impedance is HIGH as it is taken from a reverse biased PN-junction.

The Common Emitter Amplifier Circuit

In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing into the transistor as the emitter current is given as Ie = Ic + Ib.

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As the load resistance ( RL ) is connected in series with the collector, the current gain of the common emitter transistor configuration is quite large as it is the ratio of Ic/Ib. A transistors current gain is given the Greek symbol of Beta, ( β ).

As the emitter current for a common emitter configuration is defined as Ie = Ic + Ib, the ratio of Ic/Ie is called Alpha, given the Greek symbol of α. Note: that the value of Alpha will always be less than unity.

Since the electrical relationship between these three currents, Ib, Icand Ie is determined by the physical construction of the transistor itself, any small change in the base current ( Ib ), will result in a much larger change in the collector current ( Ic ).

Then, small changes in current flowing in the base will thus control the current in the emitter-collector circuit. Typically, Beta has a value between 20 and 200 for most general purpose transistors. So if a transistor has a Beta value of say 100, then one electron will flow from the base terminal for every 100 electrons flowing between the emitter-collector terminal.

By combining the expressions for both Alpha, α and Beta, β the mathematical relationship between these parameters and therefore the current gain of the transistor can be given as:

Where: “Ic” is the current flowing into the collector terminal, “Ib” is the current flowing into the base terminal and “Ie” is the current flowing out of the emitter terminal.

Then to summarise a little. This type of bipolar transistor configuration has a greater input impedance, current and power gain than that of the common base configuration but its voltage gain is much lower. The common emitter configuration is an inverting amplifier circuit. This means that the resulting output signal is 180o “out-of-phase” with the input voltage signal.

The Common Collector (CC) Configuration

In the Common Collector or grounded collector configuration, the collector is now common through the supply. The input signal is connected directly to the base, while the output is taken from the emitter load as shown. This type of configuration is commonly known as a Voltage Follower or Emitter Follower circuit.

The common collector, or emitter follower configuration is very useful for impedance matching applications because of the very high input impedance, in the region of hundreds of thousands of Ohms while having a relatively low output impedance.

The Common Collector Transistor Circuit

The common emitter configuration has a current gain approximately equal to the β value of the transistor itself. In the common collector configuration the load resistance is situated in series with the emitter so its current is equal to that of the emitter current.

As the emitter current is the combination of the collector AND the base current combined, the load resistance in this type of transistor configuration also has both the collector current and the input current of the base flowing through it. Then the current gain of the circuit is given as:

The Common Collector Current Gain

This type of bipolar transistor configuration is a non-inverting circuit in that the signal voltages ofVin and Vout are “in-phase”. It has a voltage gain that is always less than “1” (unity). The load resistance of the common collector transistor receives both the base and collector currents giving a large current gain (as with the common emitter configuration) therefore, providing good current amplification with very little voltage gain.

We can now summarise the various relationships between the transistors individual DC currents flowing through each leg and its DC current gains given above in the following table.

Relationship between DC Currents and Gains

Bipolar Transistor Summary

Then to summarise, the behaviour of the bipolar transistor in each one of the above circuit configurations is very different and produces different circuit characteristics with regards to input impedance, output impedance and gain whether this is voltage gain, current gain or power gain and this is summarised in the table below.

Bipolar Transistor Configurations

with the characteristics of the different transistor configurations given in the following table:

Characteristic	Common Base	Common Emitter	Common Collector
Input Impedance	Low	Medium	High
Output Impedance	Very High	High	Low
Phase Angle	0o	180o	0o
Voltage Gain	High	Medium	Low
Current Gain	Low	Medium	High
Power Gain	Low	Very High	Medium

In the next tutorial about Bipolar Transistors, we will look at the NPN Transistor in more detail when used in the common emitter configuration as an amplifier as this is the most widely used configuration due to its flexibility and high gain. We will also plot the output characteristics curves commonly associated with amplifier circuits as a function of the collector current to the base current.

BC184L NPN transistors

• Maximum allowed power dissipation, P = 350 mW
• Max. allowed collector current,  = 100 mA
• Max. allowed collector-emitter voltage,  = 30 V
• Typical current gain,  = 250 to 800

1. The base-emitter voltage will always be about 0·6 Volts (or ­0·6 for a PNP transistor).
2. The current gain (the  value) will be a few hundred.
3. The large  value means that , so we can assume that 
4. The circuit is driven by a +15V power line and the collector-emitter voltage is applied via the two series resistors,  & . In the absence of any good reason for making some other choice we might just as well assume that the available voltage should be shared equally between , , and the transistor. We therefore want about 5 volts across , 5 volts across , and 5 volts between the collector and emitter. This means that the amplifier should have,  V,  V, and  V.