So a few weeks ago I had to do an experiment and one of the exercises was to measure the bode plot of an op-amp. The instructions told us to measure the voltage and phase difference at the points \$TP_{37}\$ and \$R_{41}\$. During the experiment, one of the instructors told us to use \$TP_{44}\$ instead of \$R_{41}\$.
However, when I look at the schematic of the circuit, I don't understand how these points will give me the correct information. The 2nd op-amp acts like a buffer, and shouldn't change the signal in any way (theoretically), so we were told to ignore it. What's the point then of taking the ratio of \$ TP_{44} \$ and \$TP_{37}\$? To my understanding you're supposed to take the ratio of \$V_{in}\$ (= \$TP_{41}\$) and \$V_{out}\$ (= \$TP_{42} \approx TP_{44} \approx TP_{37})\$. Anyone have an idea on what the correct method is?
Anyway, I found the following transfer function for the op-amp.
$$ H(s) = \frac{-C_1}{C_2} \frac{ \frac{1}{R_1C_1} +s }{ \frac{1}{R_2C_2} + s } \\ C_1 = 220pF, \quad C_2 = 100pF, \quad R_1 = R_2 = 22k\Omega$$
.
The measured voltages:
When I take the ratio of the voltages, none of them seems to follow the magnitude of the bode plot. I know that a 100% match is very unlikely, but it doesn't even come close. I've tried different combinations.
Does anyone know what kind of op-amp setup this is? I've looked all over google images for a similar setup, but couldn't find anything. I did however find this same setup in the book "Schaum's Outlines of Electronic Devices and Circuits (2nd ed.), p288". It only confirms my transfer function.
Any advice/help is greatly appreciated.
EDIT
Some of you pointed out that I should use JP22 as my input, and I agree. I was confused since in the task they asked to look at the signals on TP37 and R41. The input signal should be 2.1V pk-pk.
Also I believe I'm supposed to calculate the bode plot of the whole circuit, not only from the first op-amp. The questions reads as:
"Measure the bode plot for voltage amplification and phase difference between input and output AC from 50Hz to 10MHz."
My apologies for this lack of clarity.