# Homework Help: Finding impedance that is unit step function

1. May 4, 2013

### anol1258

1. The problem statement, all variables and given/known data

Consider the following circuit which uses ideal components. Prior to t=0 switch S is open. Then suddenly at t=0 switch S is closed. Find the impedance $Z_{2}$ such that the system output is a unit step function of voltage. Be certain to show all components used to construct $Z_{2}$ and their connections along with component values of your design.
Z1 is Given
circuit:

2. Relevant equations

KVL, KCL, V=IR,

3. The attempt at a solution

Nothing yet. Just wanted to get this up here for now.

Last edited: May 4, 2013
2. May 4, 2013

### rude man

The output will not be a UNIT step function unless the input voltage is > 1V.

The solution furthermore is not unique. You can say pick any R2, then X2 is defined as is the voltage gain < 1.
Where Z1 = R1 + jX1 and Z2 = R2 + jX2.

3. May 5, 2013

### anol1258

Ok I understand why the input voltage has to be > 1V. So how should I start this out? Can I connect the two grounds and do a loop equation?

4. May 5, 2013

### rude man

The two grounds are already connected, by definition.

Let Z1 = R1 + jX1, Z2 = R2 + jX2, then you have a voltage divider Vout/Vin = Z1/(Z1 + Z2). In terms of the real vs. the imaginary components of that transfer function, what has to be true to make the transfer function independent of frequency?

5. May 5, 2013

### anol1258

real and imaginary must be equal?

6. May 5, 2013

### anol1258

or reactance is 0?

7. May 6, 2013

### rude man

Much better! Come up with a Z2 such that the transfer function Z1/(Z1 + Z2) has no frequency sensitivity.