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. 51 Power Consideration Total Power
0
0
中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 52