R1 represents a resistive sensor in the figure below. In reality, it has also a capacitor in parallel. I'm trying to understand the effect of this capacitor. When a parallel C(is labelled as C2) is added, the output is saturated. What is the explanation of this? How can i tackle this C which negatively affect the output?
When a parallel C(is labelled as C2) is added, the output is saturated. What is the explanation of this?
At 2 kHz, the 5 nF cap has an impedance of about 16 kohm. Because it is in parallel with a resistor of value 300 kohm, the op-amp gain is increased about twenty times and it is much more likely that the op-amp output will saturate.
How can i tackle this C which negatively affect the output?
Put a 15 nF capacitor across R5 to "balance" the effect of the 5 nF across R1. However, the op-amp output may show signs of instability so, also try a 100 ohm resistor in series with V1.
At 2kHz the impedance of C2 is 16kOhm, hence your amplifier acts like if R1 was equal to 300kOhm || 16kOhm = 15kOhm
Without the capacitor, your gain is -1/3 but with the capacitor the gain becomes -6.7 and hence you saturate the op amp (1V * 6.7 = 6.7 V pick > 5V pick)