# Homework Help: Transfer functions and cut off frequency

1. Feb 21, 2014

### nikki92

1. The problem statement, all variables and given/known data
RC parallel circuit with the resistor first and the capacitor next.

find the transfer function H(jw)

resistor first then capacitor

transfer function of a circuit with resister serial then capacitor and resister parallel

I have absolutely no background in circuits but need to understand this material to take a communications course.

3. The attempt at a solution

RC parallel would it be H(jw) = jw/(jw + 1/RC)

the other
H(jw) = jw(c/(R_s +c))/(jw + R_sC /(R_S+c)R

2. Feb 22, 2014

### Staff: Mentor

Your question is a bit vague in the way of the circuit descriptions. It would much better if you could upload a diagram or two.

3. Feb 22, 2014

### nikki92

H(jw)=jw/(jw+1/RC)

H(jw) = jw[C/(Rs+c)]/ {jw +Rsc/[(Rs+c)R ]}

H(jw) = {[1/(R1C1)] - w^2 } / {1/(R1C1) - w^2 +jw/(R2C1)}

4. Feb 22, 2014

### Staff: Mentor

Okay, that's better.

In the first diagram I interpret the output to be the capacitor current Io(t), even though the diagram is missing the current arrow on that branch. Traditionally the "o" subscript indicates an output. Your H(jw) would be correct for taking i2 as the output though.

The others are a bit more complicated to evaluate since there are several ways to simplify the expressions, and I'm not keen on spending time to see if yours can proven as identities of my own results. So. Perhaps if you could provide a bit more detail about your derivations (show and explain some intermediate steps) that would be excellent.

One thing I notice is that they have provided actual component values, so for final results they may be expecting you to plug them in for final results.