Current mirror

[Translated] Generators for generating multiple bias potentials in integrated circuits with current mirrors require relatively high voltage drops at the current source because of the series connection of several transistors and because of the threshold voltages increased in MOS circuits due to the substrate control effect, so that the transistors do not become saturated and therefore the output resistance is greatly reduced. A current mirror circuit is sought which, with high accuracy of the current mirroring, requires a small voltage drop across the current mirror output.n n n The current mirror contains a constant current source (Q) and a first transistor (T1) for a reference current (I Ref1 ). The circuit for a mirrored current (I O1 ) contains a second transistor (T2). The bases or gates of these transistors (T1, T2) are connected to one another and to the connection point of the current source (Q) and the first transistor (T1) (L1). A third transistor (T3) is connected upstream of the second transistor (T2) as a controllable resistor or regulated current source. A differential amplifier (D1) compares the potentials at the connection point of the constant current source (Q) and the first transistor (T1) and at the connection point between the second and third transistor (T2, T3) and uses the result to control the third transistor (T3) via its base or via its gate.n n n The current mirror is suitable for generators for bias potentials in integrated circuits.

KONIG WILHELM DIPL-ING

SIEMENS AG (DE)

European Patent Office