An electronic switching circuit 100’, e.g. a differential switch, suitable for controlling the flow of a very small current, such as leakage or tunnelling current, comprises first 110’, second 120’ and third 130’ terminals with the second and third terminals at substantially the same potential. A first switching element 140’, connected between the first and second terminals, enables current flow in a first mode and impedes current flow in a second mode. A second switching element 150’, connected between the first and third terminals, impedes current flow in a first mode and enables current flow in a second mode. The first and second modes are controlled by application of a control potential to the first and second switching elements, which may be CMOS transistors, or NMOS or PMOS transistor pairs. A third switching element 175 may be connected between the first terminal and the first and second switching devices to enable current flow between the first and second terminals in the first mode, and impede current flow in the second mode. A device comprising the switching circuit includes an electronic component (Fig.1B, 180), e.g. a capacitor or transistor, connected to the first terminal where, in use, a tunnelling current flows through a quantum tunnelling barrier of the electronic component. A method of operating the device and measuring the current flow is also provided.
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