Can anyone help with frequency response?

Thread Starter

thisonedude

Joined Apr 20, 2014
52
Can anyone help me approach this quesiton? I have to derive an expression for the frequency response. How do i start this question?
 

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shteii01

Joined Feb 19, 2010
4,644
Am i heading in the right direction? How do i get the Qaulity factor and the gain?
You made an error.

Think of the circuit as a voltage divider. So you have one resistor: R+Rs+jwL. Second resistor is -j/(wC). You want the voltage across the second resistor. What is the voltage divider equation looks like?
 

Thread Starter

thisonedude

Joined Apr 20, 2014
52
You made an error.

Think of the circuit as a voltage divider. So you have one resistor: R+Rs+jwL. Second resistor is -j/(wC). You want the voltage across the second resistor. What is the voltage divider equation looks like?
Oh am i missing (-j/ωC) on the bottom summation?
 

Thread Starter

thisonedude

Joined Apr 20, 2014
52
Alright after adding that, what is K? It says it is the DC gain where K = H(j0). If this is true then my H(jw) = 0 from the derivation i just made. Is this correct?
 

MrAl

Joined Jun 17, 2014
11,464
Hi,

It is more clear to write it out in terms of the variable 's' where s=jw. This makes the two complex impedances:
sL and 1/sC in shorthand notation which means s*L and 1/(s*C).

Also, for a voltage divider it is always the impedance of the lower element divided by the sum of all the element impedances.

So we would end up with:
1. The lower element: 1/sC
2. The sum: Rx+sL+1/sC
3. The division: (1/sC)/(Rx+sL+1/sC)
Note Rx=R+Rs where R and Rs are the original two resistors.

Now all that is left to do is to simplify #3 and then rearrange it into the required form to make it easier to extract the required quantities like Q.
 
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