My task was to design an instrumentation amplifier with given specifications and simulate it on LTSpiceXVII. We were told to only use one type of ac source, so to get the inverted signal I used a simple inverter design with unity gain. However, I noticed that keeping the resistance values small gave me the desired output, however increasing the resistance to large values, the output suffered drastically.
This is the circuit where I used 1kohm resistors in inverter.
And this is where I used 270kohm resistors.
I cannot figure out the reason why the simulation is giving me such results. The OP-AMPS are not totally ideal but still should behave ideally even for 270kohm resistors since the actual input resistance is of very large order. Any help would be appreciated.