1. TRANSISTOR

2. TRANSISTOR Background and Introduction A semiconductor device that Amplifies, Oscillates, or Switches the flow of current between two terminals Invention of the Transistor American physicists John Bardeen, Walter H. Brattain, and William Shockley(later jointly awarded a Nobel Prize) It was also independently developed nearly simultaneously by Herbert Mataré and Heinrich Welker, German physicists working at Westinghouse Laboratory in Paris. First Transistor Model, 1947

3. Transistor Material The transistor is an arrangement of semiconductor materials that share common physical boundaries. Materials most commonly used are Silicon gallium-arsenide and germanium Impurities have been introduced by a process called “doping”

4. TYPES OF TRANSISTOR BJT Bi Polar Junction transistor FET Field effect transistor

5. BIPOLAR JUNCTION TRANSISTORS

6. BJT A BJT (Bipolar Junction Transistor) transistor has inside two similar semi conductive materials, and between them there is a third semi conductive material of different type if the two similar materials are P and the middle one is N, then we have a P-N-P or PNP transistor. if the two materials are N and the middle one is P, then we have a N-P-N material or NPN Each transistor has 3 leads which we call base, collector and emitter, and we use the symbols b, c and e respectively The symbol of the transistor has an arrow on the emitter. If the transistor is a PNP, then the arrow points to the base of the transistor, otherwise it points to the output.

7. Types Of BJT Two basic types of bipolar junction transistor construction, 1. PNP 2. NPN, which basically describes the physical arrangement of the P-type and N-type semiconductor materials n-type semiconductors the impurities result in an excess of electrons, or negative charges p-type semiconductors the material lead to a deficiency of electrons and therefore an excess of positive charge carriers or “holes.” current regulating devices that control the amount of current flowing through them

8. NPN and PNP Transistor

9. BJT Basic construction The BJT is a three terminal device that produce two PN junctions Emitter ( E ) Base ( B ) Collector ( C ) Principle of operation of the two transistor types PNP and NPN Biasing polarity of the power supply for each type Emitter Base Collector

10. EMITTER It is highly doped To inject a large number of charge carriers Main function is to supply the majority carriers to the base. It is always forward biased with respect to base

11. BASE It is a middle section of a transistor It is lightly doped So that most of the charge carriers pass to the collector. It controls flow of charges It forms two PN junctions with Emitter and Collector

12. COLLECTOR IT IS situated opposite to the emitter It is always reversed biased So that it can collect the majority carriers Size of collector is larger than emitter Its doping level is in the middle of base and emitter

13. NPN TRANSISTOR It is constructed by two N type and One P type material. Emitter and collector are of N type material Base is of P type material It consist of two PN junctions Sandwiching a P-type layer between two n-type layers.

14. OPERATION OF NPN TRANSISTOR Forwardbackward CB E The base-emitter diode is forward biased The base-collector diode is reverse biased VBE injects the electron to the Emitter. Emitter is highly doped Base is lightly doped Collector creates electrostatic field which Attracts the electrons 95 to 99% electrons diffuses in collector region V CB V BE

15. Transistor operation With no power applied to the transistor areas There are two depletion zones between the two P-N contacts. Power source Connected b/w base and collector in reverse-bias With the positive of the source connected to the collector and the negative to the base. The depletion zone of the P-N contact between the base and the collector will be widened. A slight current will flow within this contact (due to impurities). This current is the reverse contact current symbol I CBO

16. Transistor operation Voltage supply between the emitter and the base in forward bias With the positive of the source connected to the base and the negative connected to the emitter. The depletion zone between the emitter and the base will be shortened current (electrons) will flow when the voltage exceeds a specific level. This level depends on the material that the transistor is made of. Some of the electrons that go through the e-b depletion zone, will re-connect with holes in the base. This is the base current I B symbol for reference. In real life, this current is at the scale of micro-amperes ( μ A ):

17. Cont’d Most of the electrons will flow through the base (due to spilling) and will be directed to the collector. When these electrons reach the depletion area between the base and the collector, they will experience a force from the electric field which exists in this zone, The electrons will pass through the depletion zone. The electrons will then re-connect with holes in the collector. The re-connected holes will be replaced with holes coming from the base-collector power supply (V CC ). The movement of these holes equals to a movement of electrons in the opposite direction, from the collector to the supply. In other words, the current that flows to the emitter will be divided into the small base current and the larger collector current: I E = I B + I C

18. Cont’d Generally, the number of electrons that arrive at the collector is the 99% of the total electrons, and the rest 1% causes the base current. At the collector, except the electrons that come from the emitter, there is also the reverse current from the base-collector contact Both currents flow at the same direction, so they are added I C ' = I C + I CBO

19. Transistor Parameters and Ratings The ratio of the dc collector current (I C ) to the dc base current (I B ) is the dc beta (b DC ). b DC is called the gain of a transistor: b DC = I C /I B Typical values of b DC range from less than 20 to 200 or higher. b DC is usually designated as an equivalent hybrid (h) parameter: h FE = b DC The ratio of the collector current (I C ) to the dc emitter current (I E ) is the dc alpha (a DC ). This is a less-used parameter than beta. a DC = I C /I E Typical values range from 0.95 to 0.99 or greater. a DC is always less than 1. This is because I C is always slightly less than I E by the amount of I B.

20. Cont’d There are a number of standard parameters that are used to define the performance of a transistor. Some of them are given below Type number Case Material Polarity V CEO Collector emitter voltage with base open circuit V CBO Collector base voltage with the emitter open circuit V EBO Emitter base voltage with collector open circuit I C Collector current I CM Peak collector current I BM Peak base current P TOT Total power dissipation T amb Ambient temperature T

21. Cont’d Stg Storage temperature. I CBO Collector base cut-off current I EBO Emitter base cut-off current h FE Forward current gain V CEsat Collector emitter saturation voltage V BEsat Base emitter saturation voltage C c Collector capacitance C e Emitter capacitance F t Frequency Transition

22. Introduction to Amplifiers The BJT is an excellent amplifier when biased in the forward-active region. The FET can be used as an amplifier if operated in the saturation region. In these regions, the transistors can provide high voltage, current and power gains. DC bias is provided to stabilize the operating point in the desired operation region. The DC Q-point also determines The small-signal parameters of the transistor The voltage gain, input resistance, and output resistance The maximum input and output signal amplitudes The overall power consumption of the amplifier