Importance

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Abstract

A current mirror circuit comprises first and second resistors for conducting first and second reference currents dependent upon a supply voltage, and first and second current mirrors coupled to the first and second resistors, the second resistor being in series with a voltage reference. The second current mirror mirrors the second reference current, and its mirrored current output is subtracted from the first reference current, the difference current being mirrored by the first current mirror to produce a controlled output current. The circuit can be arranged so that the controlled output current is independent of changes of the supply voltage, or, optionally with further current mirrors and voltage references, so that the controlled output current has a desired relationship with the supply voltage. A circuit is described for a cellular telephone transmitter power amplifier for which the controlled current decreases with increasing supply voltage in a working range, and decreases more rapidly beyond this range for over-voltage protection.

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First Claim