hello, I have to build an automatic gain control using an FET and an Operational Amplifier, for a phototransistor (SFH314) so that when the signal of an IR LED is weak the AGC maintains the signal, and when the signal is strong reduces it, the gate of the FET I have to control it with the phototransistor detection signal in DC once converted, and the AC signal without converting it into the Operational Amplifier and see its output with the gain control, I hope you understand, thank you very much.