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We're having trouble solving the problem with the signal system. Please help me.

happyone21

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1619958675126.png

1.Find the frequency response of this circuit.

2.Explain which filter this circuit is.

3.Find the impulse response in this circuit.

4. When x(t)=e^(-3t) u(t) is applied as input, find the output y(t).

Please, I beg of course.
 

KlausST

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Hi,

I don't call it a filter at all.

A filter has R and C in series ... which isn't the case here.

Klaus
 

andre_teprom

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Have a look on Thevenin and Norton equivalent circuits.
The leftmost resistor and current source in parallel could be replaced by an equivalent resistor and voltage source in series.
 

barry

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You don't need Rs and Cs in series to have a filter. This is a low pass filter. At low frequency, the capacitor is essentially infinite resistance. At high frequency the capacitor is essentially a short.

If you use Laplace transforms for this circuit (assuming x(t) is current and y(t) is voltage), you'll have: y(s) = x(s)*(1/R*1/sC)/(1/R+1/sC)
 
Last edited:

KlausST

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Hi,

I can´t see where it is stated that x(t) is a current.
And if x(t) is a current, then I expect y(t) to be a current, too.

Guessing x(t) is a current and guessing y(t) is a voltage ( yes I know it´s maybe the only way to give the circuit a meaningful function)
... is this the target of the homework?

***
You don't need Rs and Cs in series to have a filter. This is a low pass filter. At low frequency, the capacitor is essentially infinite resistance. At high frequency the capacitor is essentially a short.
I can´t agree.
At low frequency there is finite impedance. Only at DC there is infinite impedance.
At high frequency there still is impedance. Only at infinte frequency there is a short.
(both is not the case with x(t))

And guessing that x(t) is a current... means there is a current source, which has infinite source impedance.

***
So now one could say we don´t have to calculate with ideal parts ... but if not´it´s getting even more complicated...

***

In the end I´d say
* either it´s a trick question
* or there is a lack of information.

Klaus
 

barry

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Wouldn’t you agree at low frequency a capacitor’s impedance is really, really high? And at high frequency it’s really, really low? You don’t need zero or infinite impedance to understand the frequency response of this circuit which:

1) shows x(t) as a current source, and
2) shows y(t) obviously as a voltage.
 

KlausST

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Hi,

For sure I agree with high and low impedance...

But what I really doubt is, that it's the target of the exercise to find out that x(t) needs to be current and y(t) needs to be voltage to get useful function.

For sure people working in electronics design will find out, but I'd say at least 50% of my electronics teachers (without practical experience) are not able to find this out.

Still waiting for more information from the OP.

Klaus
 

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