| 摘要 |
A circuit (200) comprises transistors (240, 250, 260), an operational amplifier (270) and serially coupled resistors (210, 220). The circuit (200) is coupled to reference lines (201, 202). An input voltage VX on an input terminal (203) is applied across the resistors (210, 220) and divided to an output voltage VY on an output terminal (204). Output voltage VY is measured (as VM) by the operational amplifier (270). The operational amplifier (270) controls a current IA in a first current path between the reference lines (201, 202). The current IA is mirrored to a current IS in a second current path through the resistors (210, 220). The current IS is generated by one of the transistors (260) and substantially proportional to the input voltage VX. Therefore, the resistors (210, 220) do not substantially load the input and the circuit (200) exhibits a high input impedance.
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