The interesting circuit shown in the figure can have its gain digitally controlled and have two values. When the control input X is at high level (+5 V), the gain of this amplifier is -1 (inverter follower). When control input X is brought to a voltage of -5V the gain becomes +1 (non-inverting follower). Please note that the power supply for the CMOS 4066 integrated circuit (four analog / digital switches) must be symmetrical with 5-0-5 V as it operates in analog mode. The CA3140 is an operational amplifier with input field effect transistors and equivalent types can be used.
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