A four-terminal active device that can be used to perform analogue signal processing functions by means of steering or controlling current flows. The device can be thought of as a dual of the operational voltage amplifier or op-amp used in voltage-mode circuits. The current conveyor is shown in the diagram. The first-generation current conveyor, CCI, operates in the following manner: a current input to terminal X causes an identical current to flow into the other ‘input’ terminal Y; these are low-impedance inputs. The input current is also ‘conveyed’ to the output terminal Z; this is a high-impedance current source output. The second-generation current conveyor, CCII, subsequently developed, is similar except that no current flows into terminal Y. This has proved to be a more versatile device.

Current conveyor