# Difference equation of the system

Discussion in 'Homework Help' started by mo2015mo, Mar 3, 2014.

1. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
Hello my friends,,

I tried to solve the question as written in attached photo,,and I couldn't answer it correctly, ,, please help me to know where's the wrong step(s)?

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• ###### Block diagram- Modified.jpg
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Last edited: Mar 4, 2014
2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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$\text{ Y(n)=-0.3Y(n-1)+8X(n)+6.2X(n-1)}$

So confusion reigns!

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3. ### WBahn Moderator

Mar 31, 2012
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Your diagram seems a bit ambiguous to me. For instance, I'm having to guess which end of the delay element is the input and which is the output. I'm guessing that the top is the input and the bottom is the output.

Is the summing node that is feeding the x4 multiplier summing three terms? More specifically, is the signal at the bottom of that summing node going in or coming out? I'm assuming it's going in.

Your equations don't seem to mesh up with the diagram very well. You say that Eqn. 3 is -0.3*y[n-1]. But you also say that Eqn. 4 is x[n-1]. Aren't these at odds?

Your Eqn.2 doesn't reflect that third line coming up into the bottom of the summing block.

How have you concluded that the signal on the bottom line is y[n-1]?

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4. ### mo2015mo Thread Starter Member

May 9, 2013
157
1

and what is your solution steps u taken??

I sonsidered that Direct Form II block diagram and solved on it

where (a) Direct Form I block diagram (b)Direct Form II block diagram

5. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
I were drawn a wrong line ,, I'm modified this to be as attached photo..
I'm sorry for that

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6. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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In the revised case I obtained the same answer given as being correct.

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7. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
Okay .. What's method you solved of it ?? or what is wrong in my solution ??

8. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
I use a different method so it probably won't be of much use to you. I've attached for your information.

• ###### discrete feedback problem.pdf
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9. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
yes ,, it seems complex...
I have another question requires impulse response and difference equation ,, i solved it by reducing Block Diagram as attached photo,, Is it correct or Non...

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10. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
.............