1 2. Design of BJT amplifiers 2.1 Types of BJT amplifiersTypes of BJT amplifiers 2.2 BJT amplifier biasing designBJT amplifier biasing design 2.3 BJT Optimum Q pointBJT Optimum Q point 2.4CE amplifiers and DesignCE amplifiers and Design 2.5CE with R E amplifiers and DesignCE with R E amplifiers and Design 2.6EF amplifiers and DesignEF amplifiers and Design 2.7CB amplifiers and DesignCB amplifiers and Design 2.8Design of RC Coupled BJT amplifiersDesign of RC Coupled BJT amplifiers

EE Electronics Circuit Design Types of BJT amplifiers (c) Emitter Follower Very low R o and high R i Buffer applications R ac = R E //R L R dc = R E (d) Common Base Very low R i and high A V High Frequency applications R ac =( R c //R L )+(R E //R i ) R dc = R c +R E R ac = R c //R L R dc = R c +R E (a) Common Emitter High A V and low R i Voltage amplifications R ac =( R c //R L )+R E R dc = R c +R E (b) Common Emitter with R E Low A V and high R i Stability applications

EE Electronics Circuit Design BJT amplifier biasing design Designing the biasing equation R 2 Design equation V BB Design equation R 1 Design equation R B Design condition

EE Electronics Circuit Design 4 common emitter R ac = R c //R L R dc = R c +R E 1. Find V CC point 2. Draw R dc line from V CC 3. Locate Q-pt at crossing of I B and R dc line 4. Draw R ac line passing Q-pt.  V = R ac xI CQ 5. Note I CQ and V CEQ 2.3 BJT Optimum Q point

EE Electronics Circuit Design 5 6. sine wave will vary I BQ to produce I B (pp) and therefore I C (pp) and V CE (pp) will be produced. Now V CE (pp) will becomes output voltage at the collector. I C (pp) V CE (pp)=V O (pp) 6. When sine wave signal is applied to the Base circuit of BJT

EE Electronics Circuit Design 6 If Q point is at High I C When the Input wave increases I B (pp), then V CE (pp) will increase lower half cycle of the output voltage wave will be clipped due to saturate I C

EE Electronics Circuit Design 7 If Q point is at Low I C When the Input wave increases I B (pp), then V CE (pp) will increase upper half cycle of the output voltage wave will be clipped due to cutoff I C

EE Electronics Circuit Design 8 Design of Optimum Collector current (c) If the Input wave increases I BQ, then both I CQ and V CEQ will increase where both half cycle of the output voltage wave will be clipped simultaneously due to cutoff and saturation in the case shown because of optimum collector current. Optimum I CQ Design equation V o (pp) Design equation BJT Optimum Q point Design Equation

EE Electronics Circuit Design 9 Summary of Design Equations (dc design equations for all CE, CE with R E, EF, CB configurations) V BB Design equation if R B = 0.1  R E Optimum I CQ Design equation R 1 Design equation R 2 Design equation V o (pp) Design equation V BB Design equation for any R B R B Design equation if no other ac specifications are not given

EE Electronics Circuit Design 10 Design Example Draw CE amplifier circuit Draw CE amplifier circuit Design bias resistance R 1 and R 2 and find the maximum output voltage swing V o (pp) Given specifications are V CC = 5V, R C = 1k - , R L = 1k - , R E = 100  =180 Design bias resistance R 1 and R 2 and find the maximum output voltage swing V o (pp) Given specifications are V CC = 5V, R C = 1k - , R L = 1k - , R E = 100  =180 common emitter R ac = R c //R L R dc = R c +R E

EE Electronics Circuit Design CE amplifier and Design Why the circuit below is CE (Common Emitter) amplifier? 1. input to the amplifier is at Base 2. output of the amplifier is at Collector 3. so Emitter becomes common to both input and output and is called CE

EE Electronics Circuit Design 12 CE amplifier analysis 1. all capacitors short and replace V CC with ac ground 3. Calculate A v,R i, R o, A i, from the equivalent circuit 2. Then replace BJT with it ’ s equivalent circuit, label all components

EE Electronics Circuit Design 13 CE amplifier design equations (in addition to previous chapter upon dc design equations) Voltage gain Input resistance Output resistance Current gain Circuit

EE Electronics Circuit Design 14 Draw the (CE) amplifier circuit Given specifications are:  = 200, V CC = 10V, design with maximum (optimum) output voltage swing, R C = R L = 2 k  R E = 0.4 k  R i = 0, R in = 1.5 k  Design bias R 1 and R 2, find voltage gain,and undistorted output voltage swing. Example 1 CE amplifier design

EE Electronics Circuit Design 15 Draw the (CE) amplifier circuit Given specifications are:  = 200, V CC = 10V, optimum output voltage design, R C = R L = 2 k  R E = 0.4 k  R i = 0.1 k  Design bias R 1 and R 2, so that A v = v o / v i > 100 Find undistorted output voltage swing. Example 2

EE Electronics Circuit Design CE with R E amplifier and Design Why the circuit below is CE with R E amplifier? 1. input to the amplifier is at Base 2. output of the amplifier is at Collector 4. so Emitter becomes common to both input and output with R E active and is called C E with R E 3. R E is active as there is no C E

EE Electronics Circuit Design 17 CE with R E amplifier analysis 1. all capacitors short and replace V CC with ac ground 3. Calculate A v,R i, R o, A i, from the equivalent circuit 2. Then replace BJT with it ’ s equivalent circuit, label all components

EE Electronics Circuit Design 18 CE with R E amplifier design equations (in addition to previous chapter upon dc design equations) Output resistance Current gain Circuit Voltage gain Input resistance

EE Electronics Circuit Design 19 CE with R E amplifier design Draw the (CE with R E ) amplifier circuit. Given specifications are:  = 200, V CC = 11.17V,, optimum output voltage swing, R C = R L = 2 k  R E = 0.4 k  R i = 0.1 k  Design bias R 1 and R 2, so that R in = v in / i in = 10 k  find undistorted output voltage swing and voltage gain A v = v o /v in and A vT = v o /v i Example 1

EE Electronics Circuit Design EF amplifier and Design 1. input to the amplifier is at Base 2. output of the amplifier is at Emitter 3.Collector becomes common to both input and output and the amplifier is Common Collector (CC) amplifier or Emitter Follower (EF) amplifier

EE Electronics Circuit Design 21 EF amplifier analysis 1. First replace V CC with ac ground and all capacitors short.2. Then replace BJT with it ’ s equivalent circuit, label all components. 3. Calculate A v,R i, R o, A i, from the equivalent circuit

EE Electronics Circuit Design 22 To find R o all voltage sources are shorted and with it ’ s equivalent circuit, calculate R o, A i

EE Electronics Circuit Design 23 Circuit Voltage gain Input resistanceOutput resistance Current gain EF amplifier design equations (in addition to previous chapter upon dc design equations)

EE Electronics Circuit Design 24 EF amplifier design Example 1 Draw and design EF amplifier with following specifications: Specified R L = 100  = 60, V CC = 12 V Design R E, R 1, R 2, so that R in = 1 k . Find R o if R i =100  and V o (pp)

EE Electronics Circuit Design 25 Example 2 Draw and design EF amplifier with following specifications: Specified  = 60, R in = 10 k , I C = 10 mA. Design V CC, R E = R L, R 1, R 2, so that A i = 10, and find R o if R i =100  and V o (pp)

EE Electronics Circuit Design CB amplifier and Design CB amplifier without C B 1. input to the amplifier is at Emitter 2. output of the amplifier is at Collector 3. Base becomes common to both input and output and the amplifier is Common Base (CB) amplifier

EE Electronics Circuit Design CB amplifier analysis (without C B ) First replace V CC with ac ground and all capacitors short.Then replace BJT with it ’ s equivalent circuit, label all components. Calculate A v,R i, R o, A i, from the equivalent circuit

EE Electronics Circuit Design CB amplifier analysis (with C B ) R B = 0

EE Electronics Circuit Design 29 Voltage gain Input resistance Output resistance Current gain CB amplifier design equations (in addition to previous chapter upon dc design equations) CB amplifier without C B CB amplifier with C B Circuits

EE Electronics Circuit Design 30 CB amplifier design Example 1 Draw and design CB amplifier without C B with following specifications: R L = 2 k  = 100, R E = 400 , V CC = 24 V Design R 1, R 2, so that A v = 20 and find A i, R in and V o (pp)

EE Electronics Circuit Design 31 Example 2 Draw and design CB amplifier with C B for following specifications: R L = 2k  = 100, R E = 400 , V CC =  V Design R 1, R 2, so that A v =200 and find A i, R in and V o (pp)

EE Electronics Circuit Design Design of RC Coupled BJT amplifiers R i2 RiRi A V1 A V2 A VT R i2 I in ILIL RoRo Cascade amplifier consists of two or more amplifiers using individual power supply V CC for each stage. The load on the first amplifier is the input of the second amplifier and so on. For each Cascaded amplifiers, dc design is the same as before For both Cascaded amplifiers, ac design is from the followings:

EE Electronics Circuit Design 33 Design Example Draw and design a two-stage CE-CE cascade amplifier for the following specifications: V CC = 12V,  = 200 (both), R E1 = R E2 = 50  R C1 = R C2 = R L =600 ,, R i2 = 300  A i =5,000 Design the biasing resistances of the stages, R !!,R 21,R 12,R 22 # What is the V o (pp) of each stage? # What is the overall voltage gain from the first stage input V in1 to the output of the second stage V o2 ? # What is the input resistance R in1 of the first stage ? # What is the maximum possible input V in1 at the first stage? I in ILIL Second CE stage design

EE Electronics Circuit Design 34 First CE stage design