# [Microelectronic Circuits 6th Ed.] P2.27 (Regular Ed.) / P2.23 (International Ed.)

Discussion in 'Homework Help' started by Starhowl, Dec 14, 2013.

1. ### Starhowl Thread Starter New Member

Dec 3, 2013
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Can someone please explain to me what I did wrong in trying to solve this task? Or maybe I did everything right and there's an error in both the international and regular edition?

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2. ### Starhowl Thread Starter New Member

Dec 3, 2013
25
0
As far as I understand my A is in truth $A_{2}$, which instead should be $A_1$ - I still don't get it. There seems to be no way to get to that form; when looking at the solution under
http://www.***********/doc/19231397/Microelectronic-Circuits-5thEd-Solution-Manual
2.27 the author of the solution suggests, that $\Delta|G|$ seems to linearly dependent on $\Delta A$, which in fact is not true, so the solution invalid?

3. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
I haven't worked through your algebra, but algebra involving moduli is more tricky than ordinary algebra.

One equation becomes two or three as you have to consider three situations separately

Say you have to do some algebra with a modulus such as |x| then you must consider

x>0 then |x| = x
x<0 then |x| = -x
x=0 then |x| = 0

and put these separately into your equation and work it through three times.

Here is an example that actually a full professor of maths got wrong on another website!

post#6 there is correct.

4. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,297
482
That does not seem right.

x>0, then |x|=x
x<0, then |-x|=x
x=0, then |0|=0

5. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
Why not?

x<0, then |-x|=x

This is clearly wrong. if x = -15 what is |x|?

Did you read the worked example?

Last edited: Dec 14, 2013
6. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
782
Some of the links don't open for me. In any event I make the minimum open loop gain to be Aol=20,098. Does that tally?

Note:
The value was based on the assumption that the ratio R2/R1 was selected to produce a gain of exactly -100 at the aforementioned amplifier open loop gain of 20,098. The gain falls to -99.5 when the amplifier open loop gain falls to 10,049. If the ratio of R2/R1 is preset to a nominal value of 100 then the answer would be different & easier to deduce.

Last edited: Dec 15, 2013
7. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,297
482
Absolute value of negative fifteen is fifteen. In equation form I would write it the following way:
|-15|=15

8. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
Well yes, if the x is -15 then the modulus is +15.

So how can the modulus equal x, which is -15.