Current mirror circuit and method for providing zero temperature coefficient trimmable current ratios

• US 4,673,867 A
• Filed: 06/30/1986
• Issued: 06/16/1987
• Est. Priority Date: 06/30/1986
• Status: Expired due to Term

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Davis, William F.
• Primary Examiner(s): Beha, Jr., William H.
• Application Number:
  US06/879,879
• Time in Patent Office: 351 Days
• Field of Search: 323/315, 323/316, 323/907, 330/288
• US Class Current: 323/315
• CPC Class Codes: G05F 3/265 using bipolar transistors only
• CPC Class Codes: Y10S 323/907 Temperature compensation of semiconductor

Abstract

A resistively trimmed current mirror circuit including a diode coupled in parallel to the base-emitter conduction path of a transistor and to which a reference current is supplied to produce a proportional output current at the collector of the transistor. A trimmable resistor is connected in the collector-emitter conduction path of the transistor which is adjusted to vary the output current for a given reference current to trim the ratio between the two currents. By making the reference current a thermal current, i.e., a current whose magnitude is proportional to thermal voltage and inversely proportional to resistance, the trimmed ratio remains temperature independent after being trimmed to a desired value.

Claims

1. Circuit for providing an output current that is proportional to an applied input current and having first and second current paths, comprising:

current supply means for supplying a thermal current to the first current path, said thermal current having the form of (kT/qR)1n K, where k is Boltzmann'"'"'s constant, q is the charge of an electron, R is a resistance of a given resistivity and temperature coefficient, T is absolute temperature and K is a constant;

diode means coupled in the first current path through which substantially all of said thermal current flows;

a first transistor the base-emitter junction of which is coupled in a parallel conduction path with respect to said diode means and the collector-emitter junction being coupled in the second current path such that the output current flows therethrough; and

trimmable resistive means having substantially the same temperature coefficient as said resistance R for adjusting the ratio of the thermal current to said output current with said adjusted ratio being both constant and temperature independent.

2. The circuit of claim 1 wherein said diode means is a second transistor having a collector, an emitter and a base with said collector and base being shorted to said base of said first transistor and receiving said thermal current.

3. The circuit of claim 2 wherein said trimmable resistive means is a resistor connected between said emitter of said first transistor and a terminal to which is supplied ground reference potential.

4. The circuit of claim 2 wherein said trimmable resistive means is a resistor connected between said emitter of said second transistor and a terminal to which is supplied a ground reference potential.

5. The circuit of claim 2 wherein said trimmable resistive means includes;

a first resistor connected between said emitter of said first transistor and a terminal to which is supplied ground reference potential; and

a second resistor connected between said emitter of said second transistor and said terminal.

6. A current mirror circuit for providing an output current the magnitude of which is proportional to the magnitude of a supplied reference current, comprising:

current source means for supplying a thermal reference current, said thermal reference current having the form of (kT/qR)1n K, where k is Boltzmann'"'"'s constant, q is the charge of an electron, R is a resistance of a given resistivity and temperature coefficient, T is absolute temperature and K is a constant;

diode means which is forward biased by said thermal reference current;

a first transistor having a control electrode coupled to said diode means and first and second electrodes, said transistor providing said output current at said second electrode thereof; and

trimmable resistive means having substantially the same temperature coefficient as said resistance R coupled in series between said first electrode of said first transistor and a common terminal for adjusting the magnitude of the output current for a given thermal reference current wherein the adjusted ratio of the two currents is substantially temperature independent.

7. The current mirror circuit of claim 6 wherein said diode means is a second transistor having first, second and control electrodes, said control and second electrodes being interconnected to said control electrode of said first transistor and receiving said thermal reference current.

8. The current mirror circuit of claim 7 including resistive means coupled in series between said first electrode of said second transistor and said common terminal.

9. A method for adjusting the ratio of the output current to the input reference current of a current mirror circuit while maintaining the adjusted ratio substantially temperature independent, the current mirror circuit including a transistor for providing the output current at a first electrode thereof, a diode coupled in a parallel conduction path to the control-second electrode conduction path of the transistor and receiving the input reference current, and trimmable resistive means for adjusting the ratio of the reference current to the output current, comprising the steps of:

providing an input reference current having a magnitude that varies directly with absolute temperature multiplied by a constant factor and inversely to the resistance of a resistor of a given resistivity and temperature coefficient; and

adjusting the resistance of the trimmable resistive means, said resistive means having the same temperature coefficient as said resistor.

10. A current mirror arrangement including at least first and second current circuit paths, comprising:

current supply means for providing a thermal current at an output thereof of the form, (kT/qR) 1n K, where k is Boltzmann'"'"'s constant, T is absolute temperature, q is the charge of an electron, R is the resistance of a given resistivity and temperature coefficient and K is a constant;

the first current circuit path including semiconductor diode means coupled to said current supply means through which substantially all of said thermal current flows;

the second current circuit path including the collector-emitter conduction path of a first transistor the base of which is coupled to said current supply means; and

12. The current mirror of claim 10 wherein said trimmable resistive means includes:

a first resistor coupled between said diode means and a common terminal, the resistance of said first resistor being trimmable and having substantially the same temperature coefficient as said resistance of given resistivity; and

a second resistor coupled between the emitter of said first transistor and said common terminal, the resistance of said second resistor being trimmable and having substantially the same temperature coefficient as said first resistor.

13. The current mirror of claim 10 wherein:

said trimmable resistive means includes a resistor coupled between the emitter of said first transistor and a common terminal; and

said semiconductor diode means is coupled between said output of said current supply means and said common terminal.

14. The current mirror of claim 10 wherein said trimmable resistive means includes:

a resistor coupled between said semiconductor diode means and a common terminal, the resistance of said resistor being trimmable; and

means for connecting the emitter of said first transistor to said common terminal.

11. trimmable resistive means having the same temperature coefficient as said resistance for adjusting the ratio of the currents in the first and second current circuit paths with respect to one another wherein said adjusted ratio is both constant and temperature independent.