# Electronic book exercise

Discussion in 'Electronics Homework Help' started by alex0761, Aug 23, 2016.

1. ### alex0761

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Aug 23, 2016
Hi all,
I would like to submit the following exercise (from Sedra-Smith book):

Let us consider the 2 BJT large signal models shown on Figure attached (b) and (d). What are the relative dimensions of diodes DE and DB if transistor has ß=100? And if ß=1000?

What I don't understand are the results reported on book. It says that in the first case the result is 11x and in the second one the result is 1000x.
Are they correct?

Thank you 2. ### Ratch

1,093
334
Mar 10, 2013
Could you give the exact name of the book, the edition level, and the page where this problem can be found?

Ratch

3. ### alex0761

3
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Aug 23, 2016
Hi Ratch.
The book is the italian version of Sedra and Smith, Microelectronic Circuits, 5th Edition.
I translated the exercise: it is at the end of Chapter four.

4. ### Ratch

1,093
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Mar 10, 2013
I looked through the English versions of the 3, 5, and 6 editions of MicroElectronic Circuits. I did not see any problems that combine diodes and BJTs like your translation shows. I assume that your chapter is named "Diodes", right? Your translation says "dimensions", but does it really mean "junction area".. Junction area is proportional to the scale current Is. You say the answer is 11x and 1000x. Does "x" mean times? If so, times what? What is the reference? If you can find that problem in an English edition of Sedra, tell me where.

Ratch

5. ### alex0761

3
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Aug 23, 2016
Thank you Ratch.
Unfortunately I don't have the english version of the book to compare with.
The exercise is, in fact, a bit strange: that's why I asked here. It's at the end of chapter about BJTs.
I think when it asks about dimensions it means relative sizes, in terms of junction area, and, again I think, when it reports 11x it means that the ratio between the two diodes areas is 11.
It doesn't say more than what I reported, sorry.
According to you, is it possibile that, with Beta=100, the ratio between the 2 diodes areas can be 11?
I would say it should be (Beta+1), that is the same ratio between currents ib and ie.
What do you think?
Thank you for you time.

6. ### Ratch

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334
Mar 10, 2013
I found in Sedra, edition 6, a statement that confirms the size means the junction area "Since Is is directly proportional to the junction area (i.e., the device size)...". I note that in the beta=100 BJT, the diode junctions Db and De are one and the same diodes. Same with the beta=1000 BJT. Since Is is proportional to the junction area, I don't know what the problem is asking. Unless you can find some text in English that explains what is happening, I am afraid I cannot help you further.

Ratch  