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Course : Applied Electronics

Course : Applied Electronics. Course Code:22329. Teaching Scheme. Examination Scheme Theory. Examination Scheme Practical. Unit -01 Low Power Amplifier -16 Marks. Course outcome. Use transistor as low power amplifier.

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Course : Applied Electronics

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  1. Course: Applied Electronics Course Code:22329 Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  2. Teaching Scheme Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  3. Examination SchemeTheory Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  4. Examination SchemePractical Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  5. Unit -01 Low Power Amplifier -16 Marks Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  6. Course outcome Use transistor as low power amplifier Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  7. TRANSISTOR CONFIGURATIONS AND BIASING Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  8. Transistor configurations • A general two port network is • This network has input port and output port. Therefore the total number of terminals are four. Ii 2 Io 1 Two port network Output port Input port 2 1 Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  9. But transistor have only 3 terminals, hence we treat one of the three terminals “common” to input and output port. • Depending on which terminal is made common to input and output port, there are three possible configurations of transistor, they as follows: • Common base configuration • Common emitter configuration • Common collector configuration Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  10. Common Base (CB) Configuration a) NPN transistor b) PNP transistor Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  11. In CB configuration, base acts as common terminal between the input and output ports. • The input voltage VEB is applied between emitter and base while output voltage VCB is taken between collector and base. • Current relations: • The output current IC is given by IC = IC(INJ) + ICBO where IC(INJ) = injected collector current and ICBO = reverse saturation current of CB junction • As ICBO flows due to minority carriers, it is negligible as compared to IC(INJ), ∴ IC ≈ IC(INJ) • Current amplification factor (αdc): αdc = IC / IE Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  12. Common Emitter (CE) Configuration Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  13. In CE configuration, emitter acts as common terminal between input and output poets. • The input voltage VBB is applied between base and emitter while output voltage VCC is taken between collector and emitter. • Current relations: • For CB configuration, we can write IC = αdc IE + ICBO • Similarly for CE configuration, we can write IC = βdc IB + ICEO • Current gain (βdc): βdc = IC / IB Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  14. Common Collector (CC) Configuration a) NPN transistor b) PNP transistor Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  15. In CC configuration, collector acts as a common terminal between input and output. • The input voltage VEE or VBB is applied between base and collector while output voltage VCC taken between collector and emitter. • Current gain (γdc): γdc = IE / IB Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  16. Comparison of configurations Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  17. Amplification and Amplifier • Amplification: Amplification is a process of adding strength to the input signal or it is a process of “magnifying” the input signal without changing its shape. • Amplifier: • The circuit which amplifies a small input signal is called as an “amplifier”. • An amplifier is required to amplify weak signals and it is used in radio, TV, telephones, mobile phones, music system etc. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  18. Amplifier +Vdc RS IO Ii Amplifier (Voltage gain AV) RL VS Vi Vo Ri Ro Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  19. In order to magnify the input signal VS all the amplifier need a source of energy which is provided by battery or DC supply. • The dc supply is also essential for biasing the BJT used in amplifier circuits. • The amplifier should contain atleast one active device such as transistor or FET or OPAMP. • If transistor is used then it should be in the active region. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  20. Amplifier characteristics • 1. voltage gain AV and current gain AI : The gain of an amplifier is defined as the ratio of output quantity to the input quantity. ∴ AV = Vo/ Vi And AI = Io/ Ii The gain of amplifier should be as large as possible. • Input resistance (Ri): It is the resistance seen looking into the input terminals of an amplifier. Ideally Ri should be infinite. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  21. Output resistance (Ro): It is the resistance seen looking into the output terminals of an amplifier when the input signal Vi = 0 and output circuit is open circuited. Ro should be equal to zero ideally. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  22. Classification of Amplifiers Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  23. Single Stage Amplifier • Depending on which terminal of transistor is made common between input and output, the amplifiers are classified into three types as follows: • Common Emitter (CE) amplifier • Common Collector (CC) amplifier or emitter follower. • Common Base (CB) amplifier Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  24. Single stage RC coupled CE Amplifier C1 C2 CE Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  25. Fig. shows the a single stage RC coupled CE amplifier. • Circuit Components and their Functions: • Resistors: • Resistors R1, R2 and RE are used to bias the transistor in active region by using voltage divider bias circuit. • RC is collector resistor used to control collector current. 2. Input coupling capacitor C1: • The input coupling capacitor C1 is used to couple the ac input voltage VS to the base of the transistor. • As capacitor block dc, C1 couples only the ac component of the input signal. • This capacitor also ensures that the dc biasing conditions of transistor remain unchanged even after applications of the input signal. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  26. 3. Bypass capacitor CE: • As CE is connected in parallel with RE is called emitter bypass capacitor CE. • This capacitor offer a low reactance to the amplified ac signal, therefore RE gets bypassed through CE for only the ac signals. • This will increase the voltage gain of the amplifier. 4. Output coupling capacitor C2: • This capacitor couples the amplifier output to the load or to the next stage amplifier. • It is used for blocking the dc part and passing only the ac part of the amplified signal to the load. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  27. Operation of the RC coupled amplifier: • In the absence of ac input signal current IB = IBQ, IC = ICQ and voltage VCE = VCEQ. The Q point is selected to be in the active region of transistor. • As ac input signal VS is applied, the base current varies above and below IBQ. • Hence output current IC varies above and below ICQ, because IC = βIB and this variation will be large. • As the IC varies, voltage across RC will also varies, because VRC = IC x RC. • Hence collector voltage VC varies above and below VCEQ as VC = VCC – ICRC. • Through C2 only the ac part is coupled to the load. Hence Vo is of same shape as VS but of large size. • Thus amplification has taken place. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  28. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  29. Frequency Response and Bandwidth • The frequency response is graph of amplifier output voltage (or gain) versus the frequency of input signal. • Ideally frequency response should be flat over the entire frequency range. • Practically the frequency response of an amplifier is not flat over the entire operating frequency region. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  30. The practical frequency response can be divided into three regions as follows: • Low frequency region. • Mid frequency region. • High frequency region. 1. Low frequency region: In low frequency region, the gain or output voltage decreases due to the increased reactance of the coupling and bypass capacitor. 2. Mid frequency region: In this region, gain and output voltage remain constant. 3. High frequency region: In this region, the output voltage and gain will decrease due to the transistor internal capacitances and stray capacitance. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  31. Bandwidth: • Bandwidth is the band of frequencies in which the magnitude of output voltage or gain is either equal or relatively close to their mid frequency band value. • The frequencies fL and fH are called cutoff frequencies or half power frequencies. • Bandwidth of the amplifier is defined as the difference between the half power frequencies. • Lower cutoff frequency (f1 or fL): It is the frequency of the input signal at which the amplifier gain or output voltage reduce to 70.7% of their mid frequency range value. f1 is always less than f2. • Upper cutoff frequency (f2 or fH): It is the frequency of the input signal at which the amplifier output voltage reduce to 70.7% of their mid frequency range value. f2 is always higher than f1. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  32. Frequency Response Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  33. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  34. Multistage Transistor Amplifier • The multistage amplifier is obtained by cascading a number of amplifiers i.e. connecting a number of amplifier stages to each other with the output of the previous stage to the input of next stage. • The most important parameters of an amplifier are its input impedance, voltage gain, bandwidth and output resistance which are dependent on the particular applications. • In general, a single stage amplifier is not capable to fulfill all these requirements. Hence we have to use a multistage amplifier. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  35. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  36. Overall Gain of the Multistage Amplifier • Overall voltage gain: Let AV1, AV2, AV3….AVn be the voltage gain of n number stages of multistage amplifier. Then total voltage gain AV of multistage amplifier is given by AV = AV1 x AV2 x AV3 x ……. x Avn • Overall current gain: Similarly, overall current gain AI of multistage amplifier having n number of stages is given by AI = AI1 x AI2 x AI3 x …….. x AIn • Overall input resistance (Ri): the overall input resistance of a cascaded amplifier is equal to the input resistance of the first stage. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  37. Overall output resistance (Ro): The overall output resistance of a cascaded amplifier is equal to the output resistance of the last stage. • Gain in decibels: The gain expressed as a ratio of output voltage and input voltage is called as the linear gain. On the logarithmic scale the gain is expressed in decibels as follows: 1. Power gain in dB = 10 log10 [Po/ Pi] 2. Voltage gain in dB = 20 log10 [Vo/ Vi] Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  38. Methods of Coupling Multistage Amplifier • In the multistage amplifier, the output signal of preceding stage is to be connected to the input of the next stage. This is called as interstage coupling. • To achieve interstage coupling, there are three coupling techniques: 1. R-C coupling 2. Transformer coupling 3. Direct coupling Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  39. R-C coupled Amplifier Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  40. Frequency Response Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  41. Applications: • In public address (P.A.) amplifier system • Tape recorders • TV, VCR and CD players • Stereo amplifier • RC coupled amplifier are basically voltage amplifier. Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  42. Transformer Coupled Amplifier Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  43. Peaking due to resonance • Applications: • For impedance matching • For amplification of radio frequency (RF) signal. • In power amplifier • For transferring power to a low impedance load such as a loud speaker Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  44. Direct Coupled Amplifier Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  45. Applications: • In the operational amplifiers (OP-AMPS). • In the analog computations. • In the linear power supplies (voltage regulators). Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  46. Field effect Transistor Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  47. Construction Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  48. Common Source FET amplifier Applied Electronics , Mrs.S.V.Naik, E & TC Dept

  49. Tuned Amplifier

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