Hi,
I am from computer science background and very new to electronics specially analog electronics. If I ask a silly question please pardon me.
First I would like to know why op-amps need input bias current in general. If I understand correctly FET based op-amps should not need any current from input port for their operations. Is is possible to work without bias current for such op-amps?
Now more specific question I am designing a kind of capacitive antenna (see attached jpeg). It is trying to sense voltage on a remote body by doing capacitive coupling of a metal plate with it. When voltage varies on body it causes changes in metal antenna nearby. I would like to buffer this signal. Note that as antenna (metal plate) is picking up very weak signal and i understand that I would need buffer with very high input impedance. So I selected LMP2231 **broken link removed** op-amp that has typical bias current of 20fA.
I know that on body signal is 60Hz with 400mV peak to peak. But what i get at buffer output is about 2 volts or more peak-to-peak 60Hz wave . I suspect this is to do something related to bias current or too much bias current (leakage to input pin on board perhaps). Will anyone have any explanation what could be occurring in the buffer that is causing amplified signal.
Thanks & Regards,
Mandeep
I am from computer science background and very new to electronics specially analog electronics. If I ask a silly question please pardon me.
First I would like to know why op-amps need input bias current in general. If I understand correctly FET based op-amps should not need any current from input port for their operations. Is is possible to work without bias current for such op-amps?
Now more specific question I am designing a kind of capacitive antenna (see attached jpeg). It is trying to sense voltage on a remote body by doing capacitive coupling of a metal plate with it. When voltage varies on body it causes changes in metal antenna nearby. I would like to buffer this signal. Note that as antenna (metal plate) is picking up very weak signal and i understand that I would need buffer with very high input impedance. So I selected LMP2231 **broken link removed** op-amp that has typical bias current of 20fA.
I know that on body signal is 60Hz with 400mV peak to peak. But what i get at buffer output is about 2 volts or more peak-to-peak 60Hz wave . I suspect this is to do something related to bias current or too much bias current (leakage to input pin on board perhaps). Will anyone have any explanation what could be occurring in the buffer that is causing amplified signal.
Thanks & Regards,
Mandeep