High input impedance amplifier - has excess voltage protection diodes and MOSFET components in input stage

摘要

A circuit has a high input impedance (1010 ohm) amplifier with diodes to protect the amplifier input from excess voltages, MOSFET components are used, with very low input currents of some 10-13 to 10-15A, in the input stage. The diodes are arranged with cathode and anode, respectively, connected to the non-inverting input of the amplifier, while their other ends are taken via resistors to the inverting input of the amplifier. These same ends of the diodes also connect to FET's serving as electronic switches which, when closed, connect the diodes to auxiliary voltage sources that allow the diodes to conduct with low differential internal resistance. - The auxiliary voltages are selected in such a manner that the amplifier input retains the preset voltage level when the switches are closed.