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EKT104 ANALOG ELECTRONIC CIRCUITS [LITAR ELEKTRONIK ANALOG] BASIC BJT AMPLIFIER (PART III)
DR NIK ADILAH HANIN BINTI ZAHRI
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COMMON-COLLECTOR AMPLIFIER
SMALL-SIGNAL VOLTAGE GAIN INPUT AND OUTPUT IMPEDANCES SMALL-SIGNAL CURRENT GAIN
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COMMON-COLLECTOR AMPLIFIER
vO Common collector circuit (Emitter-follower) Small-signal equivalent circuit (using transconductance parameter)
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COMMON-COLLECTOR AMPLIFIER - SMALL-SIGNAL ANALYSIS: VOLTAGE GAIN-
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COMMON-COLLECTOR AMPLIFIER - SMALL-SIGNAL ANALYSIS: VOLTAGE GAIN-
Example 1: Given Rs=0.5kΩ, R1=50kΩ,R2=50kΩ,RE=2kΩ, VCC=5V, β=100, VBE(on)=0.7V and VA=80V. Calculate the small signal voltage gain of the common-collector circuit.
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COMMON-COLLECTOR AMPLIFIER - SMALL-SIGNAL ANALYSIS: VOLTAGE GAIN-
Example 1: Given Rs=0.5kΩ, R1=50kΩ,R2=50kΩ,RE=2kΩ, VCC=5V, β=100, VBE(on)=0.7V and VA=80V. Calculate the small signal voltage gain of the common-collector circuit. (Ans:ICQ=0.8mA,VCEQ=3.4V ,AV=+0.964)
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COMMON COLLECTOR AMPLIFIER -Output Impedance(Output Resistance,Ro)-
Test Current Test Voltage Small-signal equivalent circuit (using transconductance parameter), assuming source resistance, Rs to be zero The output impedance analysis on the next slide is based on this circuit.
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COMMON COLLECTOR AMPLIFIER -Output Impedance(Output Resistance,Ro)-
Vπ=-VX Let; Test Voltage Test Current
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COMMON COLLECTOR AMPLIFIER -Output Impedance(Output Resistance,Ro)-
Example 2: Given the following circuit (same as Example 1), calculate the input and output resistance. Assume the transistor & circuit parameter are;β=100, VCC=5V, VBE=0.7V, VA=80V and ro=100kΩ.
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COMMON COLLECTOR AMPLIFIER -Output Impedance(Output Resistance,Ro)-
Example 2: Given the following circuit (same as Example 1), calculate the input (Rib & Ri)and output resistance (RO). Assume the transistor & circuit parameter are;β=100, VCC=5V, VBE=0.7V, VA=80V and ro=100kΩ. (Ans:Rib =201.3kΩ ,Ri=22.2kΩ, RO=31.6 Ω)
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COMMON-COLLECTOR AMPLIFIER - Small-signal Analysis: Current Gain-
where If R1R2 Rib and ro RE then Ai (1+)
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COMMON-BASE AMPLIFIER
SMALL-SIGNAL VOLTAGE GAIN INPUT AND OUTPUT IMPEDANCES SMALL-SIGNAL CURRENT GAIN
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COMMON-BASE AMPLIFIER - Circuits-
Common-base circuit Small-signal equivalent circuit
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COMMON-BASE AMPLIFIER - Small-signal Analysis: Voltage Gain-
If RS approaches zero, then Av = gm(RC||RL)
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COMMON-BASE AMPLIFIER - Small-signal Analysis: Current Gain-
If RE approaches infinity and RL approaches zero, then;
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COMMON-BASE AMPLIFIER - Small-signal Analysis: Input Impedance-
Input resistance Ii Ib Rie Input resistance Rie = re =
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COMMON-BASE AMPLIFIER - Small-signal Analysis: Output Impedance-
Output resistance Ro Ix Vx Output resistance Ro = RC
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SUMMARY & COMPARISON Configuration Common Emitter Common Collector
Common Base Voltage Gain Av > 1 Av 1 Current Gain Ai > 1 Ai 1 Input Resistance Moderate (kΩ) High (50-100kΩ) Low (Ω) Output Resistance Moderate to High
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