Two-terminal temperature-compensated current source circuit

A two-terminal current source comprising in combination:

• (a) first and second terminals;
• (b) first, second and third transistors, the first and second transistors each having a base, a collector, and an emitter, the second transistor having a substantially greater emitter area than the first transistor, the third transistor having a control electrode, a first current-carrying electrode, and a second current-carrying electrode, the base of the first transistor being connected to the base of the second transistor;
• (c) first resistive means coupled between the emitter of the second transistor and the second terminal for producing a first current in the collector of the second transistor;
• (d) current mirroring means coupled to the collectors of the first and second transistors and the first terminal for producing a second current in the collector of the first transistor that is proportional to the first current;
• (e) second resistive means for producing a third current, coupled in series with the first and second current-carrying electrodes of the third transistor between the first and second terminals so that the third current flows through the first and second terminals;
• whereby the first and second currents have a positive temperature coefficient and the third current has a negative temperature coefficient, and a current flowing in the first and second terminals has a temperature coefficient determined by resistances of the first and second resistive means.

A two-terminal constant current source comprising in combination:

• (a) first and second terminals;
• (b) first current source means coupled between the first and second terminals for receiving only a positive temperature coefficient current from the first terminal and supplying only the positive temperature coefficient current to the second terminal, the first current source means receiving and supplying no current other than the positive temperature coefficient current;
• (c) second current source means coupled between the first and second terminals for receiving only a negative temperature coefficient current from the first terminal and supplying only the negative temperature coefficient current to the second terminal, the second current source means receiving and supplying no current other than the negative temperature coefficient current;
• (d) means for selectively controlling the magnitudes of the positive and negative temperature coefficient currents, to thereby control a temperature coefficient of a constant total current equal to the sum of the positive and negative temperature coefficient currents flowing through the first and second terminals, the constant total current being the only current flowing through either of the first and second terminals.

A method of producing a constant temperature-compensated current in first and second terminals to thereby provide a two-terminal current source, the method comprising the steps of:

• (a) supplying from the first terminal only a positive temperature coefficient current into a first current source circuit and supplying from the first current source circuit only the positive temperature coefficient current to the second terminal, the first current source receiving and supplying no current other than the positive temperature coefficient current;
• (b) supplying from the first terminal only a negative temperature coefficient current into a second current source circuit and supplying from the second current source circuit only the negative temperature coefficient current to the second terminal, the second current source circuit receiving and supplying no current other than the negative temperature coefficient current;
• and
• (c) selectively controlling the magnitudes of the positive and negative temperature coefficient currents, to control a temperature coefficient of a constant total current flowing through the first and second terminals, the total current being equal to the sum of the positive and negative temperature coefficient currents, the constant total current being the only current flowing through the first and second terminals.