- #1

Duave

- 81

- 0

__Did I answer all of the questions correctly and thoroughly? Can you please find any errors, and point them out to me so that I can fix them?__## Homework Statement

(a) Confirm these quiescent values:

V

_{B}= 8.2V

I

_{E}= 1.0 mA

(b) show that Z

_{in}for the bias network alone is 50K.

(c) Show that for high frequency ac signals Z

_{in}measured at point P2 is 500k.

(d) Show that for high frequency ac signals Z

_{in}measured at point P1 is 45.5K.

(e) show that f

_{3dB}for the entire circuit is ~ 165Hz

https://scontent-a.xx.fbcdn.net/hphotos-prn2/t1.0-9/1901740_10151937081755919_967279941_n.jpg

## Homework Equations

{R

_{110k}/(R

_{110k}+ R

_{91k})} x V

_{CC}= V

_{B}

...................

V

_{B}- V

_{BE}= V

_{E}

.................

V

_{E}/R

_{E}= I

_{E}

.....................

Z

_{bias network}= (R

_{91k})(R

_{110k})/(R

_{91k}) + (R

_{110k})

.................

Z

_{in,P2}= h

_{FE}{(r

_{e})^' + (r

_{e})}

.................

Z

_{in,P1}= (Z

_{bias network})(Z

_{in,P2})/{(Z

_{bias network}) + (Z

_{in,P2})}

.....................

f

_{3dB}= 1/(2)(pi)(Z

_{P1 - 7.5k||15k}){(C

_{0.033uF})(C

_{0.1uF})/{(C

_{0.033uF}+ (C

_{0.1uF})}}

........................

## The Attempt at a Solution

(a)

_{1}Confirm this quiescent value:

V

_{B}= 8.2V

..........

{R

_{110k}/(R

_{110k}+ R

_{91k})} x V

_{CC}= V

_{B}

.................

110k/(110k + 91k) x 15V = V

_{B}

.......

**8.2V = V**

_{B}.......

(a)

_{2}Confirm this quiescent value:

I

_{E}= 1.0 mA

......

V

_{B}- V

_{BE}= V

_{E}

..........

8.2V - 0.6V = V

_{E}

......

7.6V = V

_{E}

.....

V

_{E}/R

_{E}= I

_{E}

.........

7.6V/7.5mA = I

_{E}

.........

**1.03mA = I**

_{E}.........

1.00mA ~ I

_{E}

.........

(b) show that Z

_{in}for the bias network alone is 50K.

Z

_{bias network}= (R

_{91k})(R

_{110k})/(R

_{91k}) + (R

_{110k})

.................

Z

_{bias network}= (91k)(110k)/(91k) + (100k)

...........

**Z**

_{bias network}= 49.8k.........

Z

_{bias network}~ 50.0k

..........

(c) Show that for high frequency ac signals Z

_{in}measured at point P2 is 500k.

Z

_{in,P2}= h

_{FE}{(r

_{e})^' + (r

_{e})

...............

Z

_{in,P2}= h

_{FE}{(25mV/(I

_{C}) + (R

_{7.5k})(R

_{15k})/(R

_{7.5k}+ R

_{15k})}

.......................

I

_{C}= I

_{E}

........

Z

_{in,P2}= h

_{FE}{(25mV/[(V

_{B}- V

_{BE})/R

_{E}] + (R

_{7.5k})(R

_{15k})/(R

_{7.5k}+ R

_{15k})}

............................

Z

_{in,P2}= h

_{FE}{25mV(R

_{E})/[(V

_{B}- V

_{BE})] + (R

_{7.5k})(R

_{15k})/(R

_{7.5k}+ R

_{15k})}

............................

Z

_{in,P2}= 100{(25mV[(7.5k)/{(8.2V - 0.6V)]) + (7.5k)(15k)/(7.5k + 15k)}

...............

Z

_{in,P2}= 100{24.671(ohms) + 5k(ohms)}

..........

**Z**

_{in,P2}= 502.4k(ohms)......

Z

_{in,P2}~ 500.0k(ohms)

......

(d) Show that for high frequency ac signals Z

_{in}measured at point P2 is 45.5K.

Z

_{in,P1}= (Z

_{bias network})(Z

_{in,P2})/{(Z

_{bias network}) + (Z

_{in,P2})}

.....................

Z

_{in,P1}= {(49.8k)(502.0k)/{(49.8k) + (502.0k)}

...........

**Z**

_{in,P1}= 45.3k......

Z

_{7.5k||15k}= (7.5k)(15k)/(7.5k + 15k)

..........

Z

_{7.5k||15k}= 5k(ohms)

..........

Z

_{in,P1}- Z

_{7.5k||15k}= Z

_{P1 - 7.5k||15k}

............

45.3k - 5k = Z

_{P1 - 7.5k||15k}

.........

40.3k = Z

_{P1 - 7.5k||15k}

.........

(e) show that f

_{3dB}for the entire circuit is ~ 165Hz

f

_{3dB}= 1/(2)(pi)(Z

_{P1 - 7.5k||15k}){(C

_{0.033uF})(C

_{0.1uF})/{(C

_{0.033uF}+ (C

_{0.1uF})}}

..........................

f

_{3dB}= 1/(2)(pi)(40.3k){(0.033uF)(0.1uF)/{(0.033uF + 0.1uF)}}

..............

f

_{3dB}= 1/[(2)(pi)(40.3k){2.48x10-8}}]

.........

**f**

_{3dB}= 159.17 Hz.......

__I can see answer (e) is not 165 Hz. Where is the error? Are answers (a) - (d) correct? If not, where are the errors located?__Thanks again for your help.