Exam Spring Semester 2021 (Mock Exam)

Exam Spring Semester 2021 (Mock Exam)

by Alexandre Nicolas Lechartier -
Number of replies: 5

Dear Prof. Enz, dear TAs,

May I, please, ask some questions about the Mock exam?

1) For the problem 1, for eq. 6, could I, please, be referred to the part of the lesson (slides) that explain how to calculate R_{neq}? 

2) For the problem 1, for eq. 6, 7 & 8, what are the variables $\gamma_{nD}$ and $G_{nD}$?

3) For the problem 2, for eq. 13, why is the expression of I_{crit} not equal to n G_{mscrit} U_T, like on slide 33 of lesson 10.1 on oscillators? It looks like the n term is missing in eq. 13.

Thank you,

Alexandre

In reply to Alexandre Nicolas Lechartier

Re: Exam Spring Semester 2021 (Mock Exam)

by Hung-Chi Han -
Bonjour,

Because the answer includes many equations, so please find the attached figure for the derivation and explanation :)
Answer to mock exam 2021
Best,
Hung-Chi
In reply to Hung-Chi Han

Re: Exam Spring Semester 2021 (Mock Exam)

by Alexandre Nicolas Lechartier -
Dear Hung-Chi,

I have a question about the last question of problem 2 of the Mock exam.
I used the value of \Xi from slide 33 chap 10.1 to find I_b as in equation (15) .
I found \Xi = 1.87/3 = 1.20446 but in the exam solution it is \Xi = 1.408.
How should I calculate \Xi the right way?

Best,
Alexandre
In reply to Alexandre Nicolas Lechartier

Re: Exam Spring Semester 2021 (Mock Exam)

by Hung-Chi Han -

Hi Alexandre,

You shouldn't use the value of \chi from the slide since the amplitude A = 50 mV in the mock exam, instead of 100 mV.

But thanks to your question, I found a mistake in solution. It should be ...

x \triangleq \frac{A}{nU_T} = 1.486 \text{ ($n$ is missing in the solution)}\\ I_{B0} = 2.175\\ I_{B1} = 1.492\\ \chi \triangleq \frac{x I_{B0}}{ 2 I_{B1}} = 1.083

Here, I got the value of I_{B0} and I_{B1} by using Python Scipy module (scipy.special.iv). We will provide those values from modified Bessel function if you have this problem for the exam.

Best,

Hung-Chi
In reply to Hung-Chi Han

Re: Exam Spring Semester 2021 (Mock Exam)

by Lionel Isoz -
Hi,

If it is still useful, I think the exam correction is not wrong as we are studying the Colpitts oscillator and not the Pierce which is using x = A / (n U_T) (slide 33)
See slide 51 on oscillator course


Then to use the same abacus as the Pierce oscillator as the amplitude and current value are normalized

Hope this helps
In reply to Lionel Isoz

Re: Exam Spring Semester 2021 (Mock Exam)

by Hung-Chi Han -
Hi Lionel,

Yes! Thank you for pointing out. I am sorry about this. I should read the problem carefully.

Best,
Hung-Chi