Abstract: The input stage of an amplifier includes two input terminals to which are connected the gates of two, differentially connected, IGFETs protected by two diodes connected back-to-back (in series) between the gates. The amplifier also includes means for applying an external signal source to one input terminal, means for shorting the diode connected to the other input terminal, and means for negatively feeding back the output of the amplifier to its input. This maintains the potential difference across the diode connected to the input terminal to which the external signal source is connected close to zero volt thereby substantially eliminating any leakage current through it.