2) For the BJT amplifier shown, a) Draw the small signal circuit of the amplifier. b) Calculate the small signal input resistance (Rin) looking into the base of Q1. c) Calculate the small signal gain of the amplifier Av=vo/vi. d) What type of small signal amplifier is this CC, CE, CEWR, CB ? Beta = 100 for all transistors. VA=109 volts for Q1, VA= 5 volts for Q2 and Q3.

Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
Section: Chapter Questions
Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...
icon
Related questions
Question

Please help with this BJT problem. 

2) For the BJT amplifier shown,
a) Draw the small signal circuit of the amplifier.
b) Calculate the small signal input resistance (Rin) looking into the base of Q1.
c) Calculate the small signal gain of the amplifier Av=vo/vi.
d) What type of small signal amplifier is this CC, CE, CEWR, CB ?
Beta = 100 for all transistors. VA=109 volts for Q1, VA= 5 volts for Q2 and Q3.
1823
52.6
Transcribed Image Text:2) For the BJT amplifier shown, a) Draw the small signal circuit of the amplifier. b) Calculate the small signal input resistance (Rin) looking into the base of Q1. c) Calculate the small signal gain of the amplifier Av=vo/vi. d) What type of small signal amplifier is this CC, CE, CEWR, CB ? Beta = 100 for all transistors. VA=109 volts for Q1, VA= 5 volts for Q2 and Q3. 1823 52.6
Expert Solution
Step 1

"According to company policy we need to answer the first four subparts of a question, if you want more to get solved you should post them to a different question."

Given a BJT amplifier circuit.

We need to draw a.c equivalent circuit.

We need to calculate the small signal input resistance Rin looking into base of transistor Q1.

We also need to calculate the voltage gain of the amplifier.

Given:

VA=109 for Q1

VA=5 for Q1

Step 2

To determine the a.c resistance and output resistance by dc analysis:

D.C analysis:

Capacitors acts as open circuit and a.c voltages are deactivated.

Electrical Engineering homework question answer, step 2, image 1

Applying KVL:

10-I1×1823-VBE=0I1=10-VBE1823   =5.1 mA.Now,I1   =IC3+IB3+IB2     =IC3+2IB3 (as transistors Q2 and Q3 are identical so IB3=IB2)     =IC31+2βIC3 =I1 1+2β      =4.9 mAIC3  =IC2=4.9 mAIE1  =IC1=4.9 mAIB1  =IE1β+1      =4.9101      =48.5 μAIC1  =βIB1      =4.85 mAa.c resistance across base of transistor Q1 , rπ1=VTIB1                                                                             =26 mV48.5 μA , where VT is the thermal volatge which is equal to 26 mV at T=300K                                                                             =0.536 kΩOutput resistance due to early voltage of transistor Q1, ro1=VAIC1                                                                                       =1094.85×10-3                                                                                       =20.33 kΩOutput resistance due to early voltage of transistor Q2, ro2=VAIC2                                                                                       =54.9×10-3                                                                                       =1.02 kΩ

Thus, Output ac resistance across base of transistor Q1 is rπ1  0.536 kilo-ohm 

         Output resistance due to early voltage of transistor Q1 is ro1  20.33 kilo-ohm.

         Output resistance due to early voltage of transistor Q2 is ro2 1.02 kilo-ohm.

 

Step 3

a) To draw the a.c equivalent of the circuit:

The a.c equivalent circuit is:

Electrical Engineering homework question answer, step 3, image 1

Clearly from the a.c equivalent circuit the no input voltage across the base in transistor Q2 & Q3  so ib2 =0 & ib3=0.

So now the equivalent circuit is:

Electrical Engineering homework question answer, step 3, image 2

 

steps

Step by step

Solved in 5 steps with 3 images

Blurred answer
Knowledge Booster
BJT
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, electrical-engineering and related others by exploring similar questions and additional content below.
Recommended textbooks for you
Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
Electrical Engineering
ISBN:
9780133923605
Author:
Robert L. Boylestad
Publisher:
PEARSON
Delmar's Standard Textbook Of Electricity
Delmar's Standard Textbook Of Electricity
Electrical Engineering
ISBN:
9781337900348
Author:
Stephen L. Herman
Publisher:
Cengage Learning
Programmable Logic Controllers
Programmable Logic Controllers
Electrical Engineering
ISBN:
9780073373843
Author:
Frank D. Petruzella
Publisher:
McGraw-Hill Education
Fundamentals of Electric Circuits
Fundamentals of Electric Circuits
Electrical Engineering
ISBN:
9780078028229
Author:
Charles K Alexander, Matthew Sadiku
Publisher:
McGraw-Hill Education
Electric Circuits. (11th Edition)
Electric Circuits. (11th Edition)
Electrical Engineering
ISBN:
9780134746968
Author:
James W. Nilsson, Susan Riedel
Publisher:
PEARSON
Engineering Electromagnetics
Engineering Electromagnetics
Electrical Engineering
ISBN:
9780078028151
Author:
Hayt, William H. (william Hart), Jr, BUCK, John A.
Publisher:
Mcgraw-hill Education,