I have two sample tasks for calculating transfer functions in a circuits with operational amplifiers. I can't find any good source for solving this type of problems apart of this http://cnx.org/content/m0036/latest/, which is helpful a bit. Where to take the reference for measured voltages, and how KVL may be of any use if the circuits are opened (or am I just missing something) ?
Task 1. Phase shifter.
In proper solution I have 3 equations describing this circuit :
U1=(R+1/sC)I2
U1=2RfI2 + U2
U2=-RfI1 + (1/sC)I2
But where do we get this equations from and why ? Why U2 is not equal -U1 just as it is stated on the page from the link ? On what basis do we write the 2 equations for U1 ? Do we somehow transform this circuit ?
Task 2.
Here in solution I have only voltage transfer function given, and there are no currents arrows.
And the voltage transfer function (U2/U1) for this circuit is :
So I've tried solving this on my own :
Current in upper most wire is I3, In the middle I2 and the bottom I1.
U1 = (R3+1/sC)I2 (similar to task 1)
U1 = (R1+R2)I2 + U2 (similar to task 1)
U1 = R4I3 + U2
U2 = no idea here
Task 1. Phase shifter.
In proper solution I have 3 equations describing this circuit :
U1=(R+1/sC)I2
U1=2RfI2 + U2
U2=-RfI1 + (1/sC)I2
But where do we get this equations from and why ? Why U2 is not equal -U1 just as it is stated on the page from the link ? On what basis do we write the 2 equations for U1 ? Do we somehow transform this circuit ?
Task 2.
Here in solution I have only voltage transfer function given, and there are no currents arrows.
And the voltage transfer function (U2/U1) for this circuit is :
So I've tried solving this on my own :
Current in upper most wire is I3, In the middle I2 and the bottom I1.
U1 = (R3+1/sC)I2 (similar to task 1)
U1 = (R1+R2)I2 + U2 (similar to task 1)
U1 = R4I3 + U2
U2 = no idea here