# transfer function

Discussion in 'Homework Help' started by jstrike21, Nov 6, 2009.

1. ### jstrike21 Thread Starter Member

Sep 24, 2009
104
0
I have no idea how to do this, can someone help lead me the right way?
its problem number 2 on the pdf

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2. ### mik3 Senior Member

Feb 4, 2008
4,846
70
Did you derive the transfer function?

3. ### steveb Senior Member

Jul 3, 2008
2,431
469
The usual method is to find the transfer function in symbolic form, and then take the magnitude of the transfer function in symbolic form. To find the maximum, you can plot the graph to understand where the peak is. If the peak is not at zero or at infinity, then you can take the derivative with respect to frequency and set the expression to zero. That way you have the peak frequency in symbolic form.

However, in this case, the answer is so simple. Look at the circuit and ask yourself what kind of filter that is.

4. ### jstrike21 Thread Starter Member

Sep 24, 2009
104
0
Can I say that Vo = (Zc/Zc+R1)*Vi
With Zc being the impedance of the capacitor and R1 being the 8k resistor?

5. ### mik3 Senior Member

Feb 4, 2008
4,846
70
You have to include RL in the equation:

Vo=Vin*(Zc//RL)/[(Zc//RL)+R1]

6. ### jstrike21 Thread Starter Member

Sep 24, 2009
104
0
Ok so I have H(jw)=(jwc+(1/RL))/(jwc+(1/RL)+R1)
Is this right?

7. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
Don't think so ..

For instance if Zc//RL = Zp then

Zp=1/(jωC+(1/RL))

You seem to have missed the inverse part, as you have Zc//RL = (jωC+(1/RL))

Remember for two parallel impedances Z1 & Z2 the effective impedance Zp is defined by

1/Zp =1/Z1 + 1/Z2

or (if you prefer)

Zp=(Z1 x Z2)/(Z1+Z2)