Input/Output Impedance

Duave

The Meaning Of An Active Bandpass Filter

1. Homework Statement

Calculate the node voltages V1 and V2. Assume that the 0 ohm resistor is an ammeter, and that the zero current element is a voltmeter.

https://scontent-b.xx.fbcdn.net/hphotos-ash3/t1/1898156_10151912573775919_1335607656_n.jpg

2. Homework Equations

KVL and KCL calculation format.

3. The Attempt at a Solution

Can you please tell me if my calculations are correct.

Node 1: V1/0ohm -V1/30ohm + 100V/10ohm = 4

-V1 + 300V = 120V

V1 = 180V

Node 2: V2 = (4A)(7.5ohm)

V2 = 180V

Thank You

Last edited:
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NascentOxygen

Mentor
That's an interesting choice of title for your thread, Duave. http://physicsforums.bernhardtmediall.netdna-cdn.com/images/icons/icon5.gif [Broken]

I'm thinking you have not drawn the circuit correctly. You show the ammeter shorted out by a connecting wire. That wire also connects node 1 to node 2, making them one node. Please check and correct.

Last edited by a moderator:

NascentOxygen

Mentor
At node 1, two of the terms you will probably have are V1/10 and (V1 + 100)/30 plus some more.

Duave

Thank you for any help that you can offer.

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?

1. Homework Statement

Calculate the input impedance looking directly into the base of the BJT
Calculate the output impedance including the 3.3k resistor

https://scontent-a-pao.xx.fbcdn.net/hphotos-prn2/t1.0-9/1900003_10151939940590919_952631427_n.jpg

2. Homework Equations

Zin = (hFE + 1){ZLoad}
...................................................
Zout = {(R10k)(R3.3k)/(R10k) + (R3.3k)}/(hFE+1)
.................................................................................................................

3. The Attempt at a Solution

1(a)

Calculate the input impedance looking directly into the base of the BJT

Zin = (hFE + 1){ZLoad}
...................................................
Zin = (hFE + 1){RL
...................................................
Zin = (100 + 1){10 x 10^3(ohms)}
...................................................
Zin = (101){10 x 10^3(ohms)}
...................................................
Zin = {10.1 x 10^5(ohms)}
.....................................
Zin = {1010k(ohms)}
.....................................

1(b)

Calculate the output impedance including the 3.3k resistor

Zout = (R10k)(R3.3k)/(R10k) + (R3.3k)}/(hFE+1)
.................................................................................................................
Zout = {(10 x 10^3(ohms))(3.3 x 10^3(ohms))/(10 x 10^3(ohms)) + (3.3 x 10^3(ohms)}/(100 + 1)
.................................................................................................................
Zout = {2.481 x 10^3(ohms)}/(100 + 1)
.................................................
Zout = 24.56(ohms)
..............................

Are there any errors?

Thank you.

Jony130

Are you sure about Zout ?? Also check your numbers in Zin; ZL = ?

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• 1 person

Duave

Are you sure about Zout ?? Also check your numbers in Zin; ZL = ?
Jony130,

Okay, no, I am not sure about Zout. Seeing that my answers are not right. What assumptions can I make to improve my next attempt? What kind of questions does one ask to tackle a problem like this?

Jony130

For this simple circuit with CCCS try to find Zout = Vin/Iin for Vin = 1V and β = 100;

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Duave

For this simple circuit with CCCS try to find Zout = Vin/Iin for Vin = 1V and β = 100;
This is my answer to the question

Iin = IB + (hFE)(IB)
...................................................................
Iin = (hFE + 1)(Ib)
...................................................................
Ib = (Vin)/(Rb)
...................................................................
Iin = (hFE + 1){(Vin)/(Rb)}
.........................................................................
Zout = (Vin)/(Iin)
.........................................................................
Zout = (Vin)/[(hFE + 1){(Vin)/(Rb)}]
.............................................................................................
Zout = (Rb)/(hFE + 1)
........................................................
Zout = (10k)/(100 + 1)
........................................................
Zout = 99(ohms)
..................................................

Jony130

Very good, so Zout for your emitter follower circuit will be equal to Zout = ?

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Duave

Very good, so Zout for your emitter follower circuit will be equal to Zout = ?
So Zout = {R10k/(100 + 1)}||{R3.3k}
............................................................................................................

Jony130

Excellent work

• 1 person

Duave

Very good, so Zout for your emitter follower circuit will be equal to Zout = ?
Excellent work
Okay this is a revision of the whole problem. Can you please look at all eight questions and answers? Thanks Jony130.

Thank you for any help that you can offer.

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?

1. Homework Statement

Calculate the input impedance looking directly into the base of the BJT
Calculate the output impedance including the 3.3k resistor
Calculate VB neglecting loading of the bias network by the BJT
Calculate VE neglecting loading of the bias network by the BJT
Calculate IE neglecting loading of the bias network by the BJT
Calculate VB including loading of the bias network by the BJT
Calculate VE including loading of the bias network by the BJT
Calculate IE including loading of the bias network by the BJT

https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-frc1/t1.0-9/1932404_10151940102460919_638617745_n.jpg

1(a): Calculate the input impedance looking directly into the base of the BJT

Zin = (hFE + 1){ZLoad}
...................................................
Zin = (hFE + 1){R10k
...................................................
Zin = (100 + 1){10 x 10^3(ohms)}
...................................................
Zin = (101){10 x 10^3(ohms)}
...................................................
Zin = {10.1 x 10^5(ohms)}
.....................................
Zin = {1010k(ohms)}
.....................................

1(b): Calculate the output impedance including the 3.3k resistor

Iin = [IB + (hFE)(IB)]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
...................................................................
Iin = [(hFE + 1)(Ib)]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
...................................................................
Ib = [(Vin)/(Rb)]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
...................................................................
Iin = [(hFE + 1){(Vin)/(Rb)}]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
.........................................................................
Zout = {(Vin)/(Iin)}{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
.........................................................................
Zout = (Vin)/[(hFE + 1){(Vin)/(Rb)}]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
.............................................................................................
Zout = {(Rb)/(hFE + 1)}{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
..................................................................................................................................
Zout = {(10k)/(100 + 1)}{3.3k}/{(10k)/(100 + 1)} + {3.3k}
.....................................................................
Zout = 96(ohms)
..................................................

https://scontent-a-pao.xx.fbcdn.net/hphotos-prn1/t1.0-9/1964785_10151940672820919_881396491_n.jpg

2(a): Calculate VB including loading of the bias network by the BJT

rin = (hFE + 1){R}
...................................................
rin = (hFE + 1){R7.5k
...................................................
rin = (100 + 1){7.5 x 10^3(ohms)}
...................................................
rin = (101){7.5 x 10^3(ohms)}
...................................................
rin = {7.575 x 10^5(ohms)}
.....................................
rin = {757.5k(ohms)}
.....................................

IB = IE/(hFE + 1)
...................................................
IB = {(VCC/R7.5k)/(hFE + 1)}
.................................................................................
IB = {(15V/7.5k/(100 + 1)}
..........................................
IB = {(15V/7.5k/(100 + 1)}
..........................................
IB = 1.98 x 10^-5
..........................................
IB = 19.8uA
..........................................
VB = (rin)(IB)
................................................
VB = (757.5k)(19.8uA)
..................................
VB = (757.5k)(19.8uA)
..................................
VB = 15V
.............................

2(b): Calculate VE including loading of the bias network by the BJT

VE = VB - VBE
................................................
VE = 15V - 0.6V
............................
VE = 14.4V
............................

2(C): Calculate IE including loading of the bias network by the BJT

IE = IE/R7.5k
................................................
IE = 14.4V/7.5k
................................................
IE = 1.92mA
................................................

2(D): Calculate VB neglecting loading of the bias network by the BJT

{R150k/(R150k + R130k)} x VCC = VB
.........................................................................................
150k/(150k + 130k) x 15V = VB
.......................................
8.03V = VB
........................................

2(E): Calculate VE neglecting loading of the bias network by the BJT

VE = VB - VBE
................................................
VE = 8.03V - 0.6V
............................
VE = 7.43V
............................

2(F): Calculate IE neglecting loading of the bias network by the BJT

IE = IE/R7.5k
................................................
IE = 7.43V/7.5k
................................................
IE = 0.99mA
................................................

Are there any errors?

Thanks again for your help.

Duave

NascentOxygen,

This is a whole problem. Can you please look at all eight questions and answers and tell me if you see errors?

Thank you for any help that you can offer.

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?

1. Homework Statement

Calculate the input impedance looking directly into the base of the BJT
Calculate the output impedance including the 3.3k resistor
Calculate VB neglecting loading of the bias network by the BJT
Calculate VE neglecting loading of the bias network by the BJT
Calculate IE neglecting loading of the bias network by the BJT
Calculate VB including loading of the bias network by the BJT
Calculate VE including loading of the bias network by the BJT
Calculate IE including loading of the bias network by the BJT

https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-frc1/t1.0-9/1932404_10151940102460919_638617745_n.jpg

1(a): Calculate the input impedance looking directly into the base of the BJT

Zin = (hFE + 1){ZLoad}
...................................................
Zin = (hFE + 1){R10k
...................................................
Zin = (100 + 1){10 x 10^3(ohms)}
...................................................
Zin = (101){10 x 10^3(ohms)}
...................................................
Zin = {10.1 x 10^5(ohms)}
.....................................
Zin = {1010k(ohms)}
.....................................

1(b): Calculate the output impedance including the 3.3k resistor

Iin = [IB + (hFE)(IB)]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
...................................................................
Iin = [(hFE + 1)(Ib)]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
...................................................................
Ib = [(Vin)/(Rb)]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
...................................................................
Iin = [(hFE + 1){(Vin)/(Rb)}]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
.........................................................................
Zout = {(Vin)/(Iin)}{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
.........................................................................
Zout = (Vin)/[(hFE + 1){(Vin)/(Rb)}]{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
.............................................................................................
Zout = {(Rb)/(hFE + 1)}{R3.3k}/{(R10k)/(100 + 1)} + {R3.3k}
..................................................................................................................................
Zout = {(10k)/(100 + 1)}{3.3k}/{(10k)/(100 + 1)} + {3.3k}
.....................................................................
Zout = 96(ohms)
..................................................

https://scontent-a-pao.xx.fbcdn.net/hphotos-prn1/t1.0-9/1964785_10151940672820919_881396491_n.jpg

2(a): Calculate VB including loading of the bias network by the BJT

rin = (hFE + 1){R}
...................................................
rin = (hFE + 1){R7.5k
...................................................
rin = (100 + 1){7.5 x 10^3(ohms)}
...................................................
rin = (101){7.5 x 10^3(ohms)}
...................................................
rin = {7.575 x 10^5(ohms)}
.....................................
rin = {757.5k(ohms)}
.....................................

IB = IE/(hFE + 1)
...................................................
IB = {(VCC/R7.5k)/(hFE + 1)}
.................................................................................
IB = {(15V/7.5k/(100 + 1)}
..........................................
IB = {(15V/7.5k/(100 + 1)}
..........................................
IB = 1.98 x 10^-5
..........................................
IB = 19.8uA
..........................................
VB = (rin)(IB)
................................................
VB = (757.5k)(19.8uA)
..................................
VB = (757.5k)(19.8uA)
..................................
VB = 15V
.............................

2(b): Calculate VE including loading of the bias network by the BJT

VE = VB - VBE
................................................
VE = 15V - 0.6V
............................
VE = 14.4V
............................

2(C): Calculate IE including loading of the bias network by the BJT

IE = IE/R7.5k
................................................
IE = 14.4V/7.5k
................................................
IE = 1.92mA
................................................

2(D): Calculate VB neglecting loading of the bias network by the BJT

{R150k/(R150k + R130k)} x VCC = VB
.........................................................................................
150k/(150k + 130k) x 15V = VB
.......................................
8.03V = VB
........................................

2(E): Calculate VE neglecting loading of the bias network by the BJT

VE = VB - VBE
................................................
VE = 8.03V - 0.6V
............................
VE = 7.43V
............................

2(F): Calculate IE neglecting loading of the bias network by the BJT

IE = IE/R7.5k
................................................
IE = 7.43V/7.5k
................................................
IE = 0.99mA
................................................

Are there any errors?

Thanks again for your help.

berkeman

Mentor
The ammeter is shorted out, as NO says. There is likely an error in your original post. Can you please check with the instructor?

berkeman

Mentor
Thread closed while we sort out multiple posts of the same question...

berkeman

Mentor

"Input/Output Impedance"

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