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Basic BJT Amplifiers CO2005: Electronics I Basic BJT Amplifiers 張大中 中央大學 通訊工程系 [email protected] 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 1 The Bipolar Linear Amplifier To use the circuit as an amplifier, the transistor needs to be biased with a dc voltage at a quiescent point (Q-point), such that the transistor is biased in the forward-active region. If the transistor is not biased in the active region, the output voltage does not change with a change in the input voltage. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 2 The Bipolar Linear Amplifier To obtain a linear amplifier, the time-varying or ac currents and voltages must be small enough to ensure a linear relation between the ac signals. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 3 Analysis of AC Circuit (Small Signal Analysis) Assume that the transistor is baised in the forward-active region with appropriate dc voltages and currents. BE is forward-biased, iE I S exp(vBE /VT ) I I I i S exp(v /V ) S exp((V v ) /V ) S exp(V /V )exp(v /V ) B 1 BE T 1 BEQ be T 1 BEQ T be T I BQ exp(vbe /VT ) I BQ (1vbe /VT ) I BQ ib ib (I BQ /VT )vbe Similarly, we have: DC Components: VBB I BQ RB VBEQ iB I BQ ib VCC ICQ RC VCEQ iC ICQ ic DC+AC Components: vCE VCEQ vce VBB vs iB RB vBE (I BQ ib )RB (VBEQ vbe ) vBE VBEQ vbe VCC iC RC vCE (ICQ ic )RC (VCEQ vce ) AC Components: vs ibRB vbe ic RC vce 0 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 4 Small Signal Hybrid-Equivalent Circuit vbe ibr 1 i I B S exp(v /V ) r v v 1 BE T BE Q BE Q 1 I I S exp(v /V ) BQ V 1 BE T V T Q T r : diffusion resistance iC I S exp(vBE /VT ) iC iC 1 ICQ I S exp(vBE /VT ) gm vBE vBE Q VT VT gm : transconductance VT ICQ rgm I BQ VT 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 5 Small Signal Hybrid-Equivalent Circuit iC iC iB iB Q i i c C ib iB Q 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 6 Small Signal Hybrid-Equivalent Circuit Vo gmVbeRC Vo IbRC r Vs Vbe ( )Vs Ib r RB r RB Vo r Vo RC Av gmRC Av Vs r RB Vs r RB 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 7 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 8 DC and AC Circuit Model 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 9 Bipolar AC Analysis 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 10 Small Signal Equivalent Circuit Including Early Effect iC I S exp(vBE /VT )(1vCE /VT ) VA : is the Early voltage The output resistance is v 1 i 1 ICQ r CE C I exp(v /V ) o i r v S BE T V V C Q o CE Q A A 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 11 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 12 Small Signal Hybrid-Equivalent Circuit for PNP BJT 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 13 Small Signal Hybrid-Equivalent Circuit for PNP BJT 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 14 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 15 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 16 Two Port Network Model 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 17 Common-Emitter Amplifier A. DC analysis B. AC analysis 6.3 VT 0.026 3 Vth 12 0.756V r 100 10 2.736K 93.7 6.3 ICQ 0.95 R 93.7K // 6.3K 5.9K VA 100 3 th ro 10 105K 0.756 0.7 ICQ 0.95 I 9.5A B v 1 6.3// 93.7 // r 5.9K i v 0.288v I 100I 0.95mA b s s C B r r 6.3// 93.7 // r 0.5 vo ib (ro // RC ) 1000.288vs 5.67 163.23vs 12V 6K Rth Vth 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 18 Common Emitter amplifier 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 19 Common-Emitter Circuit with Emitter Resistor A. DC analysis B. AC analysis 12.2 VT 0.026 Vth 10 1.79V r 100 1.2K 56 12.2 ICQ 2.16 R 56K //12.2K 10K v th i s 0.1168v ,mA 1.79 0.7 s 10//(r (1) 0.4) 0.5 s I 0.0216mA B 10 (1100) 0.4 10 ib is 0.1938is ,mA 10 (r (1) 0.4) IC 100I B 2.16mA 10V vo ib RC 1000.19380.1168vs 2 4.527vs 2K Rth Vth 0.4K 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 20 Amplification Stability ….. independent of 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 21 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 22 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 23 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 24 Common Emitter Circuit with Emitter Bypass Capacitor We can use an emitter bypass capacitor to effectively short out a portion or all of the emitter resistance to enhance the small-signal voltage gain. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 25 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 26 Common-Emitter Circuit with Current Source 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 27 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 28 AC Load Line DC Load Line: AC Load Line: 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 29 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 30 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 31 Maximum Symmetrical Swing When symmetrical sinusoidal signals are applied to the input of an amplifier, symmetrical sinusoidal signals are generated at the output. AC load can be used to determine the maximum output symmetrical swing. If the output exceeds the limit, a portion of the output signal will be clipped and signal distortion will occurs. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 32 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 33 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 34 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 35 Common-Collector Amplifier (Emitter-Follower) 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 36 Common-Collector Amplifier (Emitter-Follower) Small-Signal Voltage Gain Ib :Base Input Current Vo Ib (1)(ro // RE ) Rib r (1)(ro // RE ) Ib Vb / Rib (Vb Vin ) (1)(ro // RE ) Vo Vb r (1)(ro // RE ) Ri Vb Vs Rs Ri Ri R1 // R2 // Rib Vo (1)(ro // RE ) R1 // R2 // Rib Av Vs r (1)(ro // RE ) Rs R1 // R2 // Rib 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 37 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 38 Common-Collector Amplifier (Emitter-Follower) Input Impedance Rib r (1)(ro // RE ) Ri R1 // R2 // Rib Vs Ii Rs R1 // R2 //(r (1)(ro // RE )) Output Impedance V I x b r R // R // R s 1 2 Ib V V I x (1) x x I ro // RE r Rs // R1 // R2 b 1 I x Ro Vx R // R // R r // R r Rs // R1 // R2 s 1 2 o E Ro // ro // RE 1 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 39 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 40 Common-Collector Amplifier (Emitter-Follower) Small-Signal Current Gain 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 41 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 42 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 43 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 44 Common-Base Amplifier Small-Signal Voltage Gain (ro ) V I x b Vx V r V V V V s x x (1) x Rs RE r Vs 1 1 1 ( )Vx Rs Rs RE r r Vs I Vx b Vx (Rs // RE // ) 1 Rs Vo gmV(RC // RL ) r Vs gm (RC // RL )(Rs // RE // ) Ib 1 Rs gm (RC // RL ) r Av (Rs // RE // ) gm (RC // RL ) (Rs 0) Rs 1 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 45 Common-Base Amplifier Small-Signal Current Gain V V I x (1) x I i Vx b RE r 1 1 Vx RE r V I s b RE //(r/(1)) r Vs gmVRC gm RC I V Vx (Rs // RE // ) Vs o s 1 R RC RL RC RL s as Rs 0 Io gm RC r Ai RE // Ii RC RL 1 R , R R , A 1 E C L i 1 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 46 Common-Base Amplifier Input Impedance Ii (1)Ib V Ibr Rie V/ Ii r/(1) Output Impedance V (Rs // RE // r)gmV [1(Rs // RE // r)gm ]V 0 V 0 Ro RC Rs // RE // r 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 47 Multistage Amplifiers: Cascade Configuration V R A o g g (R // R )(R // r ) is v m1 m2 C 2 L C1 2 Ris R1 // R2 // r1 Vs Rs Ris 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 48 Darlington Pair Configuration I1 I3 I2 I1 1Ii Ai Io / Ii 12 2 1 12 Ri r1 (11)r2 I2 (11)Ii 1VT (1 1)VT 2 I3 2 I2 2 (11)Ii r1 (1 1)r2 ICQ1 ICQ2 Io I1 I3 (12 2 1)Ii Ri (1 1)r2 (11)r2 2(1 1)r2 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 49 Multistage Amplifiers: Cascode Configuration V1 Vs 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 50 Power Consideration DC Power Total Current and Voltage 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed.
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