Bipolar Junction Transistors
The Bipolar Junction Transistor (BJT) is an active nonlinear device that consists of three terminals. These terminals are called collector (C), base (B) and emitter (E). The BJT is a current-controlled device and it behaves like a switch. Its on state depends on a specific amount of voltage necessary to turn the device on: this threshold voltage is called VBE(ON) or VEB(ON) and it’s about 0.3V for germanium transistors or 0.7V for silicon transistors. BJTs come in two types: NPN and PNP. Under normal operating conditions, in NPN transistors the BE junction is forward-biased while the BC junction is reverse-biased. Similarly, in PNP transistors the EB junction is forward-biased while the CB junction is reverse-biased.
0
V1
0Vdc
I1 Q1
0 I
0Adc V Q2N2222
0
NPN BJT (Q2N2222)
The transistor is off until VBE reaches about 0.6V. Then the transistor turns on and there are two possibilities: if VCE is less than 0.2V the transistor is in the saturation region whereas if VCE is more than 0.2V the transistor is in the active/linear region.
In the active/linear region the collector current stays fairly constant and that is where the transistor typically operates.
1 www.ice77.net 20mA saturation
15mA
active/linear
10mA
5mA
0A 0V 1V 2V 3V 4V 5V 6V 7V 8V 9V 10V IC(Q1) V_V1
DC sweep (IC/VCE)
The IC/VCE characteristics are plotted above (IC is on the Y axis and VCE is on the X axis). The graph is a DC sweep generated by a primary DC voltage source (0V to 10V) and a secondary DC current source (10µA to 100µA). The sweep shows 10 different collector currents (all in red), each one of them generated by a specific base current (increments of 10µA). At the bottom, a 10µA base current produces a 1.5mA collector current in the active/linear region.
750mV
700mV
650mV
600mV
550mV 0V 1V 2V 3V 4V 5V 6V 7V 8V 9V 10V V(I1:-) V_V1 DC sweep (VBE/VCE)
The VBE/VCE characteristics are shown above (VBE is on the Y axis and VCE is on the X axis). The graph is a DC sweep generated by a primary DC voltage source (0V to 10V) and a secondary DC current source (10µA to 100µA). The sweep shows 10 different voltages across the BE junction (all in green), each one of them generated by a specific base current (increments of 10µA). At the bottom, a 10µA base current sets the voltage of the BE junction to 657mV in the active/linear region.
2 www.ice77.net BJT characteristics
C E
NPN N -VEB+ P Ic P Q2 Ie N Q1 N P B Ib B Ib +VCE- +VEC- Q2N2222 Q2N2906 Ie PNP Ic +VBE- VBE=0.7V VEB=0.7V
E C
CURRENT-VOLTAGE CHARACTERISTICS IN THE ACTIVE/LINEAR REGION
DC parameters EARLY EFFECT
NPN PNP V V BE V EB V nVT CE nVT EC I C I S e 1 I C I S e 1 I E I C I B VA VA
I C I E ( 1) I B (50<β<300) I B 1
I C I C I B I E (0.980<α<0.997) I E 1 I C VBE nVT ln I S
AC parameters TRANSCONDUCTANCE
VA VCE VA I C ro g m I C I C VT r re
VT VT VT VT re r 1 re I E I C g m I B I C g m
PARAMETRIC SWEEP FOR THE COMMON EMITTER CONFIGURATION
20mA saturation
0 VCE(min)=0.2V VBC(max)=0.5V 15mA
V1 active/linear 0Vdc 10mA
I1 Q1
0 I 5mA 0Adc Q2N2222
0A 0V 1V 2V 3V 4V 5V 6V 7V 8V 9V 10V IC(Q1) V_V1 0
3 www.ice77.net Facts about BJTs
1. The BJT was invented in 1947 by Bardeen, Brattain and Shockley. 2. Early BJTs were made of germanium (Ge). Modern BJTs are made of silicon (Si). 3. An NPN transistor has an n-type collector, a p-type base and an n-type emitter. Electrons are minority carriers in the base and they define the type of current in the device. 4. In an NPN transistor, the emitter is heavily doped (n+) while the collector is lightly doped (n). 5. BJTs are bipolar devices because their operation depends on electrons and holes rather than either electrons or holes like in MOSFETs. 6. The emitter takes its name from the fact it is the emitter of charge carriers (electrons for NPN and holes for PNP). 7. NPN transistors are more popular than PNP transistors because electron mobility is higher than hole mobility in semiconductors. This translates into higher current and faster operation.
8. BJTs, when compared to MOSFETs, have higher transconductance (gm) for
same output current (iC versus iD). 9. BJTs are preferred over MOSFETs for most analog applications. 10. BJTs and MOSFETs can be combined into BiCMOS to use advantages of both technologies. 11. Heterojunction Bipolar Transistors (HBTs) are improved BJTs that can handle high frequencies. They are made of silicon-germanium (Si-Ge) or aluminum gallium arsenide (AlGaAs). Essentially, they are high-speed BJTs. 12. BJTs are preferred over MOSFETs for very high-frequency applications such as radio-frequency circuits for wireless systems.
4 www.ice77.net Common Emitter Configuration
VCC
VCC
20.00V
20.00V RC 869.7uA
R1 200.5uA 10k
90k CC VCC
11.30V 0V 10uF V 20.00V Q1 Rs CB 869.7uA 20Vdc 5.359uA VCC 0A 0V 1.952V RL V 50 10uF Q2N2222 -875.0uA 1.313V 20k 1.070mA 0AVs 875.0uA 0A VOFF = 0V REAC 0V VAMPL = 500mV R2 195.2uA FREQ = 1kHz 500
10k 0 0V 875.0uA REDC CE 0 0V 1k 470uF 0 0 0 0 Common Emitter Configuration
The Common Emitter Configuration features a grounded emitter. However, in the above schematic, two emitter resistors and a capacitor are also present. The components are introduced to ensure stability and avoid clipping of the output waveform. The load is connected to the collector.
8.0V
4.0V
0V
-4.0V
-8.0V 0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0ms V(CC:2) V(Vs:+) Time Time domain sweep at 1kHz
The voltage gain is greater than 1 and the output is 180° out of phase with respect to the input.
5 www.ice77.net VCC
VCC
20.00V
20.00V RC 869.7uA
R1 200.5uA 10k
90k CC VCC
11.30V 0V 10uF V 20.00V Q1 Rs CB 869.7uA 20Vdc 5.359uA VCC 0A 0V 1.952V RL V 50 10uF Q2N2222 -875.0uA 1.313V 20k 1.070mA 0AVs 875.0uA 0A 500mVac REAC 0V 0Vdc R2 195.2uA 500
10k 0 0V 875.0uA REDC CE 0 0V 1k 470uF 0 0 0 0 Common Emitter Configuration
8.0V
6.0V
4.0V
2.0V
0V 10mHz 1.0Hz 100Hz 10KHz 1.0MHz 100MHz 10GHz V(CC:2) V(Vs:+) Frequency AC sweep from 10mHz to 10GHz
The amplifier is linear from about 2.5Hz to 7.5MHz. The voltage gain in the midband is about 12. REAC increases input resistance and lowers the voltage gain but it can also distort the output. CE lowers the low –3dB frequency point.
6 www.ice77.net Common Collector Configuration
VCC
VCC
20.00V
20.00V
R1 169.0uA
20k VCC
20.00V Q1 Rs CB 15.82mA 20Vdc 85.86uA VCC 0A 0V 16.62V V 50 10uF Q2N2222 -15.90mA CE 15.99mA 15.90V 0AVs 0V VOFF = 0V 15.90V 0V VAMPL = 500mV R2 83.10uA 15.90mA 10uF V FREQ = 1kHz RE
200k 0 0V 1k RL
0V 20k 0A 0 0 0 0V
0 Common Collector Configuration
The Common Collector Configuration features an AC grounded collector. The load is connected to the emitter.
500mV
0V
SEL>> -500mV V(Vs:+) 500mV
0V
-500mV 0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0ms V(RL:2) Time Time domain sweep at 1kHz
The voltage gain is close to 1 and the output is in phase with respect to the input.
7 www.ice77.net VCC
VCC
20.00V
20.00V
R1 169.0uA
20k VCC
20.00V Q1 Rs CB 15.82mA 20Vdc 85.86uA VCC 0A 0V 16.62V V 50 10uF Q2N2222 -15.90mA CE 15.99mA 15.90V 0AVs 0V 500mVac 15.90V 0V 0Vdc R2 83.10uA 15.90mA 10uF V RE
200k 0 0V 1k RL
0V 20k 0A 0 0 0 0V
0 Common Collector Configuration
500mV
400mV
300mV
200mV
100mV
0V 10mHz 1.0Hz 100Hz 10KHz 1.0MHz 100MHz 10GHz 1.0THz V(Vs:+) V(RL:2) Frequency AC sweep from 10mHz to 1THz
The amplifier is linear from about 1.4Hz to 587MHz. The voltage gain in the midband is almost 1. This amplifier is often called Emitter Follower.
8 www.ice77.net Common Base Configuration
V+
RC 4.265mA
1k
V+ CC V+ V- 1.736V 0V R1 81.36uA 10uF V 6.000V -6.000V RL 6Vdc -6Vdc 60k 4.265mA V+ 4.290mAV-
1.119V 25.43uA Q1 20k 0A 55.93uA Q2N2222 4.346mA CB R2 -4.290mA 0 0V 0V 434.9mV 100uF 20k 0 0 CE Rs 0V0V 0A
V 100uF 50 V 4.290mA 0V 0 RE 0AV1 VOFF = 0V VAMPL = 50mV 1.5k FREQ = 1kHz
V- 0 Common Base Configuration
The Common Base Configuration features an AC grounded base. In the above schematic the two resistors at the base are used to bias the transistor. The load is connected to the collector and the voltage gain is the ratio of the voltage at the output over the voltage at the emitter.
1.0V
0.5V
0V
-0.5V
-1.0V 0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0ms V(CC:2) V(V1:+) V(CE:1) Time Time domain sweep at 1kHz
The voltage gain is greater than 1 and the output is in phase with respect to the input.
9 www.ice77.net V+
RC 4.265mA
1k
V+ CC V+ V- 1.736V 0V R1 81.36uA 10uF V 6.000V -6.000V RL 6Vdc -6Vdc 60k 4.265mA V+ 4.290mAV-
1.119V 25.43uA Q1 20k 0A 55.93uA Q2N2222 4.346mA CB R2 -4.290mA 0 0V 0V 434.9mV 100uF 20k 0 0 CE Rs 0V0V 0A
V 100uF 50 V 4.290mA 0V 0 RE 0AV2 50mVac 0Vdc 1.5k
V- 0 Common Base Configuration
1.0V
0.5V
0V 10mHz 1.0Hz 100Hz 10KHz 1.0MHz 100MHz 10GHz V(RL:2) V(Rs:1) V(CE:1) Frequency AC sweep from 10mHz to 10GHz
The amplifier is linear from about 28.5Hz to 22.95MHz. The voltage gain in the midband is about 145 (VC/VE).
The highest gain attainable by a BJT amplifier is provided by the Common Base Configuration.
The highest bandwidth attainable by a BJT amplifier is provided by the Common Collector Configuration.
10 www.ice77.net Multistage BJT amplifier I
VCC VCC VCC
20.00V VCC VCC 1.032mA V2 20.00V R14 1.032mA VCC VCC 200.6uA 10k 20Vdc R9 20.00V R12 3.699mA 10k 9.676V C4 1.032mA 200.6uA 90k 0V 0V 20.00V 10u R4 R7 V Q3 0 200.6uA 10k 90k C3 1.032mA 1.943V R2 9.676V 6.367uA RL 10u Q2N2222 Q2 90k C2 1.032mA -1.039mA 10k 1.943V 0A 6.367uA 194.3uA 1.299V 10u Q2N2222 R13 Q1 R1 C1 1.032mA -1.039mA 1.039mA 1.943V 10k R15 0A 6.367uA 194.3uA 1.299V 0 50 10u Q2N2222 R8 250 V 0V -1.039mA 1.039mA 10k R10 0V 0AV1 194.3uA 1.299V 1.039V VOFF = 0V R3 250 VAMPL = 1mV 1.039mA 0 1.039mA FREQ = 1kHz 10k R5 0V 1.039V R16 250 C7 0 1.039mA 1k 0V 0V 1.039V 10u 1.039mA R11
0 0 R6 C5 1k C6 0 0 1k 10u 10u
0 0 0 0 Multistage BJT amplifier I
A sequence of Common Emitter amplifiers can be combined to produce higher gain but reduced bandwidth.
1.0mV
0V
SEL>> -1.0mV V(V1:+) 5.0V
0V
-5.0V 0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0ms V(RL:2) Time Time domain sweep at 1kHz
The voltage gain is about 4271 and the output is 180° out of phase with respect to the input.
11 www.ice77.net VCC VCC VCC
20.00V VCC VCC 1.032mA V2 20.00V R14 1.032mA VCC VCC 200.6uA 10k 20Vdc R9 20.00V R12 3.699mA 10k 9.676V C4 1.032mA 200.6uA 90k 0V 0V 20.00V 10u R4 R7 V Q3 0 200.6uA 10k 90k C3 1.032mA 1.943V R2 9.676V 6.367uA RL 10u Q2N2222 Q2 90k C2 1.032mA -1.039mA 10k 1.943V 0A 6.367uA 194.3uA 1.299V 10u Q2N2222 R13 Q1 R1 C1 1.032mA -1.039mA 1.039mA 1.943V 10k R15 0A 6.367uA 194.3uA 1.299V 0 50 10u 250 V Q2N2222 R8 0V -1.039mA 1.039mA 10k R10 0V 0AV1 194.3uA 1.299V 1.039V 1mVac R3 250 0Vdc 1.039mA 0 1.039mA 10k R5 0V 1.039V R16 250 C7 0 1.039mA 1k 0V 0V 1.039V 10u 1.039mA R11
0 0 R6 C5 1k C6 0 0 1k 10u 10u
0 0 0 0 Multistage BJT amplifier I
800mV
600mV
400mV
200mV
0V 100mHz 1.0Hz 10Hz 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHz 1.0GHz V(RL:2) V(R1:1) Frequency AC sweep from 100mHz to 1GHz
The amplifier is linear from 133Hz to 294kHz. The voltage gain in the midband is about 4271. The gain is high so the bandwidth is reduced.
12 www.ice77.net Multistage BJT amplifier II
V+ V-
20.00V 20Vdc 2.423mA V+ V+ V-
V+ V+ V+ V+ 20Vdc 9.918mA
0V 20.00V R6 104.6uA 20.00V R3 2.881mA 0 0 2.409mA 150k R12 R1 403.5uA 5k 4k Q2 40k 5.598VC2 3.617mA
4.310V18.39uA 10.37V 10uF Q2N2222 -3.636mA Q3 Q2N2222 C6 Q1 Rs C1 2.881mA -2.423mA 17.42uA 4.227V 2.409mA 0V 0A 0V 3.861V C4 20uF R10 R11 V 50 10uF Q2N2222 14.13uA 10uF V V+ -2.898mA2.898mA 3.636V 0 489.4uA 0V R9 2.423mA 10k 30k 503.5uA 3.188V R4 R7 86.21uA 0AV1 R2 386.1uA R8 3.636mA 4.894V VOFF = 0V 10k 0A VAMPL = 1mV 100 50k -20.00V RL FREQ = 1kHz 10k 1k C5 V- 20k 0V 2.898V 10uF 0V 2.898mA 0V R5 C3 0 1k 10uF
0 0 0 0 0 0 0 Multistage BJT amplifier II
The three configurations of the BJT can be combined in sequence. In the above schematic the amplifier has three stages: CE, CC and CB (left to right). The combination of these produces high gain and moderate bandwidth.
1.0mV
0V
SEL>> -1.0mV V(V1:+) 4.0V
0V
-4.0V 0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 3.0ms 3.5ms 4.0ms 4.5ms 5.0ms V(C6:1) Time Time domain sweep at 1kHz
The voltage gain is about 3262 and the output is 180° out of phase with respect to the input.
13 www.ice77.net V+ V-
20.00V 20Vdc 2.423mA V+ V+ V-
V+ V+ V+ V+ 20Vdc 9.918mA
0V 20.00V R6 104.6uA 20.00V R3 2.881mA 0 0 2.409mA 150k R12 R1 403.5uA 5k 4k Q2 40k 5.598VC2 3.617mA
4.310V18.39uA 10.37V 10uF Q2N2222 -3.636mA Q3 Q2N2222 C6 Q1 Rs C1 2.881mA -2.423mA 17.42uA 4.227V 2.409mA 0V 0A 0V 3.861V C4 20uF R10 R11 V 50 10uF Q2N2222 14.13uA 10uF V V+ -2.898mA2.898mA 3.636V 0 489.4uA 0V R9 2.423mA 10k 30k 503.5uA 3.188V R4 R7 86.21uA 0AV1 R2 386.1uA R8 3.636mA 4.894V 1mVac 10k 0A 0Vdc 100 50k -20.00V RL 10k 1k C5 V- 20k 0V 2.898V 10uF 0V 2.898mA 0V R5 C3 0 1k 10uF
0 0 0 0 0 0 0 Multistage BJT amplifier II
4.0V
3.0V
2.0V
1.0V
0V 10mHz 1.0Hz 100Hz 10KHz 1.0MHz 100MHz 10GHz V(C6:1) V(V1:+) Frequency AC sweep from 10mHz to 10GHz
The amplifier is linear from about 288Hz to 1.602MHz. The voltage gain in the midband is about 3262. The gain is high so the bandwidth is reduced.
14 www.ice77.net Bipolar Junction Transistor
AC/SMALL-SIGNAL ANALYSIS - MIDBAND
Common emitter configuration
Vcc
Rc ic R2
C
+ Q1 B
+ 40239 Vout R1 E Vin
R3 - -
0 0 0
R1 R2
B C Vout
+ + ic=gmVbe
Vin rpi r0 Rc Vout
-
E -
0 0
R3
1 R1 r R2 r0 || RC R3 re g m g m
Vout ic r0 || RC r0 RC Vout ic RC Vin VBE
Vout ic RC gmVBE RC AV gm RC Vin VBE VBE
15 www.ice77.net Bipolar Junction Transistor
AC/SMALL-SIGNAL ANALYSIS - MIDBAND
Common emitter configuration
Vcc
Vcc
Rc
Vout R1
Rs
RL
Vs R2
0 0 0 0
Rin Rout
Rs Vin B C Vout
+ ic=gmVpi Vs RB=R1||R2 Vpi rpi ro Rc RL
-
E 0 0 0 0 0 0 0
Rin RB || r Rout ro || Rc
Vin V Vout gmV ro || Rc || RL
Vout g mV ro || Rc || RL Av g m ro || Rc || RL Vin V
Properties: high voltage gain, high input resistance, reduced bandwidth (Miller effect)
16 www.ice77.net Common emitter configuration with degeneration
Vcc
Vcc
Rc
Vout R1
Rs
RL
Vs R2 REAC
0
0 0 REDC
0 0
Rin Rout
Rs Vin B C Vout
+ ic=Bib Vpi rpi ro Vs RB=R1||R2 - Rc RL
E
+
Ve REAC 0 0 0 0 -
0
Rin RB || r 1 REAC RB || 1REAC re * * Rout ro || Rc Rc ro ro 1 g m REAC
Vin V Ve ibr ib ic REAC ibr ie REAC ibr ib 1REAC ib r 1 REAC
ib 1 REAC re
Vout ib Rc || RL
Vout ib Rc || RL Rc || RL Rc || RL Av Vin ib 1 REAC re 1 REAC re REAC re
Properties: REAC increases the input resistance and lowers the voltage gain
17 www.ice77.net Common collector/Emitter follower configuration
Vcc
Vcc
R1
Rs
Vout Vs R2
RE RL
0 0 0 0
Rin Rout
Rs B Vin rpi E Vout
+ Vpi -
Vs ic=Bib RB=R1||R2 ro RE RL
C
0 0 0 0 0 0
Rin RB || r 1 ro || RE || RL RB || 1re ro || RE || RL r R || R R r || R || B S out o E 1
Vin ibr ib 1 ro || RE || RL ib r 1ro || RE || RL
Vout ib 1 Rout || RL
Vout ib 1 Rout || RL 1Rout || RL Rout || RL Av Vin ib r 1 ro || RE || RL r 1 ro || RE || RL re ro || RE || RL
Properties: voltage gain close to 1, very high input resistance, very low output resistance
18 www.ice77.net Common base configuration
Vcc
Vcc
Rc
Vout R1
RL
R2
RE Rs 0
0 0 Vs
VEE
0
ro
Rin Rout ic=aie
Rs E Vin C Vout
- Vs RE re Rc RL Vpi ie
+
0 0 0 0 0 B
Actual circuit
19 www.ice77.net Rin Rout
Rs E Vin C Vout
- ic=aie Vs RE re Rc RL Vpi ie
+
0 0 0 B 0 0 0
Simplified circuit
Rin RE || re Rout ro || RC RC
Vin V iere Vout ie RC || RL
Vout ie RC || RL RC || RL Av g m RC || RL Vin iere re
Properties: very high voltage gain, very low input resistance, high bandwidth
20 www.ice77.net Bipolar Junction Transistor
AC/SMALL-SIGNAL ANALYSIS - LOW FREQUENCY
The bandwidth of the BJT is limited in the low frequency range by the external capacitances CB, CC and CE. These capacitances set the lower cutoff frequency fL.
Common emitter configuration
Vcc
Vcc
Rc
Cc Vout R1
Rs CB
RL
Vs R2
0
0 0 0
Rs CB B C Cc
+ ic=gmVpi Vs RB=R1||R2 Vpi rpi ro Rc RL
-
E 0 0 0 0 0 0 0
B RS RB || r CB C ro || RC RL CC
n 1 L L f L n 2
21 www.ice77.net Common emitter configuration with degeneration
Vcc
Vcc
Rc
Cc Vout R1
Rs CB
RL
Vs R2 REAC
0 CE 0 0 REDC
0 0
Rs CB B C Cc
+ ic=gmVpi Vpi rpi ro Vs RB=R1||R2 - Rc RL
E
REAC 0 0 0 0
REDC CE
0 0
B RS RB || r REAC || ro RC || RL CB RS RB || r REAC CB
r R || R S B C RL RC || ro REAC || CC RL RC CC 1
r R || R r R || R S B S B E REDC || REAC || ro RC || RL CE REDC || REAC CE 1 1
n 1 L L f L n 2
22 www.ice77.net Common collector configuration
Vcc
Vcc
R1
Rs CB
CE Vout Vs R2
RE RL
0 0
0 0
Rs CB B rpi E CE
+ Vbe -
Vs ic=gmVbe RB=R1||R2 ro RE RL
C
0 0 0 0 0 0
B ro || RE || RL r || RB RS CB
E RS || RB r || ro || RE RL CE
n 1 L L f L n 2
23 www.ice77.net Common base configuration
Vcc
Vcc
Rc
Cc Vout R1
CB
RL
CE
R2
RE Rs 0
0 0 Vs
VEE
0
ro
ic=aie
Rs CE E C Cc
- Vs RE re Rc RL Vpi
+
0 0 0 0 0 B Actual circuit
24 www.ice77.net ic=aie
Rs CE E C Cc
- Vs RE re Rc RL Vpi
+
0 0 0 0 0 B Simplified circuit
E RS RE || re CE
C RC RL CC
n 1 L L f L n 2
25 www.ice77.net Bipolar Junction Transistor
AC/SMALL-SIGNAL ANALYSIS - HIGH FREQUENCY
The bandwidth of the BJT is limited in the high frequency range by the internal capacitances Cπ and Cμ. These capacitances set the higher cutoff frequency fH.
Common emitter configuration
Vcc
Vcc
Rc
Cc Vout R1
Rs CB
RL
Vs R2
0 0 0 0 Rs B Cmu C
+ ic=gmVpi Vs RB=R1||R2 Vpi rpi Cpi ro Rc RL
-
E 0 0 0 0 0 0 0 0 Actual circuit Rs B C
+ ic=gm*Vpi Vs RB=R1||R2 Vpi rpi Cpi CM ro Rc RL CL
-
E 0 0 0 0 0 0 0 0 0 0 Simplified circuit
i RS ||RB || r C CM CM C (1 K ) 1 o ro || RC || RL CL CL C 1 C K 1 f H H n H 2 n
26 www.ice77.net Common emitter configuration with degeneration
Vcc
Vcc
Rc
Cc Vout R1
Rs CB
RL
Vs R2 REAC
0 CE 0 0 REDC
0 0
Rs B Cmu C
+ ic=gmVbe Vbe rpi ro Vs Cpi RB=R1||R2 - Rc RL
E
REAC 0 0 0 0
0 Actual circuit
Rs B C
+
Vs ic=gm*Vbe RB=R1||R2 Vbe rpi* Cpi* CM ro* Rc RL CL
-
0 0 0 0 0 0 0 0 0 0 E Simplified circuit
* g m g m 1 g m REAC
27 www.ice77.net * * i RS || RB || r C CM
* * C r r 1 g m REAC C CM C (1 K ) 1 g m REAC * o ro || RC || RL CL
* 1 ro ro 1 g m REAC CL C 1 C K 1 f H H n H 2 n
28 www.ice77.net Common collector configuration
Vcc
Vcc
R1
Rs CB
CE Vout Vs R2
RE RL
0 0 0 0
Cpi
Rs B rpi E
+ Vbe -
Vs ic=gmVbe RB=R1||R2 Cmu ro RE RL CL
C 0 0 0 0 0 0 0 0 Actual circuit
Rs B E
Vs ic=gmVbe RB=R1||R2 rpi* Cmu CM ro rpi** RE RL CL
C 0 0 0 0 0 0 0 0 0 0 0 Simplified circuit
* i RS || RB || r C CM r r * C C (1 K) 1 K M ** o ro || r || RE || RL CL r 1 r ** C C 1 C 1 L K 1 K 1 f H H n H 2 n
29 www.ice77.net Common base configuration
Vcc
Vcc
Rc
Cc Vout R1
CB
RL
CE
R2
RE Rs 0
0 0 Vs
VEE
0
ro
ic=aie
Rs E C
- Vs RE re Cpi Rc RL Cmu Vpi
+
0 0 0 0 B 0 0 0 Actual circuit
30 www.ice77.net ic=aie
Rs E C
- Vs RE re Cpi Rc RL Cmu Vpi
+
0 0 0 0 B 0 0 0 Simplified circuit
i RS || RE || re C
o RC || RL C
1 f H H n H 2 n
Note: the common base configuration is not affected by Miller capacitance because the base of the amplifier is grounded.
31 www.ice77.net