Bandgap reference circuit
The disclosed bandgap circuit is configured to provide a temperature stable reference current and/or voltage that is also adjustable. The stability can be facilitated by an improved matching of current mirrors provided by a source degeneration topology. The source degeneration can reduce random mismatches without requiring increased size or complexity of the current mirrors and can facilitate operation of the current mirrors in a weak inversion condition, in which random mismatches may be most severe. Further, the source degeneration may be adjusted to adjust a level and/or a temperature coefficient of the generated reference current and/or voltage.
1. A method for generating a reference current, the method comprising:
generating a proportional-to-absolute-temperature (PTAT) current;
generating a complementary-to-absolute-temperature (CTAT) current;
generating a first copy of the PTAT current using a PTAT current mirror with source degeneration adjustable by an adjustable resistance;
generating a first copy of the CTAT current using a CTAT current mirror with source degeneration adjustable by an adjustable resistance; and
combining the first copy of the PTAT current and the first copy of the CTAT current to generate a first reference current with a first temperature coefficient.
2. The method for generating a reference current according to claim 1 , further comprising:
adjusting the source degeneration of one or both of the CTAT current mirror and the PTAT current mirror to obtain a second reference current with a second temperature coefficient.
3. The method for generating a reference current according to claim 2 , wherein:
the PTAT current mirror includes a first input transistor coupled at a source terminal to a first source degeneration resistor and a first output transistor coupled at a source terminal to a second source degeneration resistor;
the CTAT current mirror includes a second input transistor coupled at a source terminal to a third source degeneration resistor and a second output transistor coupled at a source terminal to a fourth source degeneration resistor; and
the adjusting the source degeneration of one or both of the CTAT current mirror and the PTAT current mirror includes adjusting a resistance of any of the first source degeneration resistor, the second source degeneration resistor, the third source degeneration resistor, or the fourth source degeneration resistor.
4. The method for generating a reference current according to claim 1 , further comprising:
inputting the first reference current to a first output resistor to obtain a first reference voltage.
5. The method for generating a reference current according to claim 4 , further comprising:
adjusting a resistance of the first output resistor to change the first reference voltage.
6. The method for generating a reference current according to claim 1 , wherein the PTAT current mirror is in a cascode configuration, and the CTAT current mirror is in a cascode configuration.
7. The method for generating a reference current according to claim 1 , further comprising:
coupling the reference current to an output current mirror with source degeneration, the output current mirror with source degeneration including a plurality of output transistors, each output transistor coupled at a source terminal to a source degeneration resistor; and
adjusting a particular source degeneration resistor to adjust a temperature coefficient of a current conducted by a particular output transistor coupled to the particular source degeneration resistor.
8. A bandgap reference circuit, comprising:
a current generator configured to generate a proportional-to-absolute-temperature (PTAT) current and a complementary-to-absolute-temperature (CTAT) current;
a PTAT current mirror with source degeneration coupled to the current generator and configured to generate at least one copy of the PTAT current, the source degeneration of the PTAT current mirror being adjustable to adjust a level of each of the at least one copy of the PTAT current;
a CTAT current mirror with source degeneration coupled to the current generator and configured to generate at least one copy of the CTAT current, the source degeneration of the CTAT current mirror being adjustable to adjust a level of each of the at least one copy of the CTAT current; and
at least one output configured to combine one of the at least one copy of the PTAT current with one of the at least one copy of the CTAT current to generate a reference current.
9. The bandgap reference circuit according to claim 8 , wherein the current generator includes:
a first diode-connected transistor and a second diode-connected transistor that are biased to produce a voltage difference across a first resistor that is proportional to absolute temperature, the voltage difference across the first resistor generating the PTAT current; and
an amplifier configured to couple a voltage of the first diode-connected transistor, which is complementary to absolute temperature, to a second resistor to generate the CTAT current.
10. The bandgap reference circuit according to claim 8 , wherein:
the PTAT current mirror with source degeneration includes:
a PTAT current mirror input transistor having a source terminal coupled to a corresponding source degeneration resistor, and
at least one PTAT current mirror output transistors, each of the at least one PTAT current mirror output transistors having a source terminal coupled to a corresponding source degeneration resistor; and
the CTAT current mirror with source degeneration includes:
a CTAT current mirror input transistor having a source terminal coupled to a corresponding source degeneration resistor, and
at least one CTAT current mirror output transistors, each of the at least one CTAT current mirror output transistors having a source terminal coupled to a corresponding source degeneration resistor.
11. The bandgap reference circuit according to claim 10 , wherein the PTAT current mirror input transistor, the at least one PTAT current mirror output transistors, the CTAT current mirror input transistor, and the at least one CTAT current mirror output transistors are P-type metal oxide semiconductor (MOS) transistors.
12. The bandgap reference circuit according to claim 10 , wherein the PTAT current mirror input transistor, the at least one PTAT current mirror output transistors, the CTAT current mirror input transistor, and the at least one CTAT current mirror output transistors are operated in a weak inversion condition.
13. The bandgap reference circuit according to claim 10 , wherein:
the source degeneration resistors corresponding to the at least one PTAT current mirror output transistors are adjustable; and
the source degeneration resistors corresponding to the at least one CTAT current mirror output transistors are adjustable.
14. The bandgap reference circuit according to claim 13 , wherein:
an adjustment to the source degeneration resistors controls a level of the reference current.
15. The bandgap reference circuit according to claim 13 , wherein:
an adjustment to the source degeneration resistors controls a temperature coefficient of the reference current.
16. The bandgap reference circuit according to claim 8 , wherein the at least one output includes an output resistor to generate a reference voltage.
17. The bandgap reference circuit according to claim 16 , wherein the output resistor can be adjusted to change a level of the reference voltage.
18. A bandgap reference circuit, comprising:
a current generator configured to generate a proportional-to-absolute-temperature (PTAT) current and a complementary-to-absolute-temperature (CTAT) current;
a PTAT current mirror with source degeneration coupled to the current generator and configured to generate at least one copy of the PTAT current, the PTAT current mirror in a cascode configuration;
a CTAT current mirror with source degeneration coupled to the current generator and configured to generate at least one copy of the CTAT current the CTAT current mirror in the cascode configuration; and
at least one output configured to combine one of the at least one copy of the PTAT current with one of the at least one copy of the CTAT current to generate a reference current.
19. The bandgap reference circuit according to claim 18 , wherein the at least one output includes an output current mirror configured to generate one or more copies of the reference current.