Variable resistance circuit
AssigneeTokyo Shibaura Denki Kabushiki Kaisha
InventorTatsuo Tanaka
Life of this patent
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Abstract
A variable resistance circuit includes an emitter-follower transistor having a base coupled to an input terminal, a collector and an emitter; a resistance element inserted between the emitter of the emitter-follower transistor and an output terminal; a current mirror circuit whose current input circuit is coupled to the collector of the emitter-follower transistor and whose current output circuit is coupled to the output terminal; and a control circuit coupled to the current mirror circuit. The current mirror operation of the current mirror circuit is controlled by a control signal so that an effective impedance measured from the output terminal is changed according to the control signal. In above the circuit the effective impedance at the output terminal may have plural values according to the control signal.
Claims13
A variable resistance circuit comprising:
- an emitter-follower transistor having a base coupled to an input terminal, a collector and an emitter;
- an impedance element coupled between the emitter of said emitter-follower transistor and an output terminal;
- a current mirror circuit whose current input circuit is coupled to the collector of said emitter-follower transistor and whose current output circuit is coupled to said output terminal, a current flowing from said current output circuit being substantially proportional to a current flowing from said current input circuit according to the current mirror operation of said current mirror circuit;
- and
- control circuit means responsive to a control signal and coupled to said current mirror circuit, a proportional relation between currents of the current input and current output circuits of said current mirror circuit being controlled by said control signal so that an effective impedance measured from said output terminal is changed according to said control signal.
A variable resistance circuit comprising:
- a transistor having a base connected to an input terminal;
- a resistor connected between an emitter of said transistor and an output terminal;
- a current mirror circuit having an input-side transistor which is inserted between a collector of said transistor and a power source, and an output-side transistor which is current-mirror connected to said input-side transistor and which is connected to said power source and one end of said resistor at the side of said output terminal;
- and
- an electronic switch which is connected between said power source and a node between bases of said input- and output-side transistors of said current mirror circuit, a switching operation of which is controlled by a switch control signal.
Dependencies are inferred from the claim text.