Low voltage current mirror and CTAT current source and method

A complementary-to-absolute temperature (CTAT) current source suitable for use with a low supply voltage, comprising:

• first and second resistances, one terminal of each resistance connected to a common node,
• a first bipolar transistor having its base and emitter connected to the terminals of said first and second resistances opposite said common node, respectively,
• a second transistor having a control input and a current circuit with first and second current terminals, the current through said current circuit varying with the voltage applied to said control input. said second transistor having its control input connected to said common node and its current circuit connected to a supply voltage and supplying current through said first and second resistances, and
• a third transistor connected to mirror the current supplied by said second transistor, said mirrored current being the output of said CTAT current source,
• said first bipolar transistor when turned on imposing its base-emitter voltage V.sub.be across said resistances thereby inducing a CTAT current through them, said resistances arranged to limit the voltage across said second transistor to a preselected fraction of said first transistor's V.sub.be sufficient to operate said second transistor in its active region.

A complementary-to-absolute temperature (CTAT) current source, comprising:

• a resistance,
• a first bipolar transistor having its base and emitter connected across said resistance,
• a second transistor having a control input and a current circuit with first and second current terminals, the current through said current circuit varying with the voltage applied to said control input, said second transistor having its control input connected to said first transistor's emitter and its current circuit connected to a supply voltage and supplying current through said resistance, and
• a third transistor connected to mirror the current supplied by said second transistor through said resistance, said mirrored current being the output of the current source,
• said first bipolar transistor when turned on imposing its base-emitter voltage V.sub.be across said resistance thereby creating a CTAT current through it.

A current mirror circuit suitable for use with a low supply voltage, comprising:

• a resistance having first and second terminals,
• first and second transistors connected in a cascode configuration between a first supply voltage and the first terminal of said resistance, said first and second transistors' control inputs connected to the first and second terminals of said resistance, respectively,
• a programming current source connected to supply a current through said resistance which develops a voltage across it, and
• third and fourth cascoded transistors having their bases connected to the respective bases of said first and second transistors and arranged to mirror the current through said first and second transistors, said fourth transistor providing said mirrored current as the output of said current mirror,
• said voltage across said resistance establishing a voltage across said first transistor sufficient to operate said first transistor in its active region.