All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > Homework Help

Notices

Homework Help Stuck on a textbook question or coursework? Cramming for a test and need help understanding something? Post your questions and attempts here and let others help.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 03-16-2012, 02:47 AM
DrWatts DrWatts is offline
New Member
 
Join Date: Mar 2012
Posts: 1
Default Output Signal Swing of CE amplifier

Hey all, I ran into a wall while trying to design a common emitter amplifier. I was wondering if someone here would be able to point me in the right direction:

Specifications:
Common Emitter BJT amplifier with an Emitter Resistance and two coupling capacitors (assumed infinite for now)
Transistor 2N2222 (assume =100 and )





Design Goals:
Voltage Gain of -20 V/V
Output Voltage Swing ΔV=10V peak-to-peak
Input Resistance greater than 10kΩ

Attempt at Solution:
I thought to set to best bias the circuit. Thus . This would give a transconductance of .

Since the signal generator impedance is low:





The gain equation is . We can solve for . Which makes , , and .



I'm using a rule of thumb and making the current through the voltage divider equal to one tenth of the emitter current. Thus . Since the sum of the two resistances needs to equal and the voltage divider has to make , then and .




Finally, the collector current will be at a maximum when the amplifier is in saturation:










So by my math, the output signal should be linear up to 13Vpp. However, when I simulate this in SPICE (0.5V signal at 1kHz), my output signal is clipped above at 6.5V. I am sure that there is small mistake somewhere, but I have been unable to pick it out. I can provide more detail on how I derived my equations if necessary. Any suggestions on where to go from here?

P.S.: Sorry for the poor formatting, this is my first post!

Last edited by DrWatts; 03-16-2012 at 02:53 AM.
Reply With Quote
  #2  
Old 03-16-2012, 09:29 PM
Ron H's Avatar
Ron H Ron H is offline
E-book Developer
 
Join Date: Apr 2005
Location: Idaho, USA (GMT-7)
Posts: 7,050
Default

I don't believe you included the capacitor and the 47k load resistor in your calculations.
Keep in mind that the cap always has 7.5V across it. When the transistor cuts off, you are left with a series circuit between +15V and ground consisting of 10k, 7.5V, and 47k. This means that the peak current into the load is (15-7.5)/(10k+47k). Multiply this current by the 47k load resistance, and you get the peak output voltage.
Reply With Quote
Reply   Post New Thread

Tags
, , ,


Related Site Pages
Section Title
Worksheet Performance-based assessments for analog integrated circuit competencies
Worksheet Performance-based assessments for semiconductor circuit competencies
Worksheet Class A BJT amplifiers
Worksheet Bipolar junction transistors in active mode
Textbook BJT quirks : Bipolar Junction Transistors
Textbook Feedback : Bipolar Junction Transistors
Textbook Biasing calculations : Bipolar Junction Transistors
Textbook The cascode amplifier : Bipolar Junction Transistors
Textbook The common-collector amplifier : Bipolar Junction Transistors
Textbook The common-emitter amplifier : Bipolar Junction Transistors


Similar Threads
Thread Thread Starter Forum Replies Last Post
Small Signal BJT Amplifier kaname08 The Projects Forum 27 03-09-2012 03:35 PM
Do guitar pedals draw guitar signal when there is no amp connected at their output? icydash The Projects Forum 25 07-05-2011 11:21 PM
Problem with output power-linear amplifier tzitzikas Radio and Communications 11 05-28-2010 10:15 PM
Help regarding audio amplifier.. sarang2502 General Electronics Chat 16 04-27-2010 10:16 PM
Television Aerial Signal Amplifier JUAN DELA CRUZ General Electronics Chat 17 06-03-2008 02:33 AM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 11:21 AM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin
Copyright ©2000 - 2014, vBulletin Solutions, Inc.