Bandgap circuit with noise reduction and temperature stability
A bandgap reference circuit includes a complimentary to absolute temperature (CTAT) current generator providing a CTAT current with a source degeneration resistor, and a proportional to absolute temperature (PTAT) current generator providing a PTAT current. The PTAT current generator includes a first branch with a source degeneration resistor, a first p-type metal-oxide semiconductor (PMOS) transistor, and a first n-type metal oxide semiconductor (NMOS) transistor, a resistor, and a diode-connected transistor. A second branch includes a source degeneration resistor, a second PMOS transistor, a second NMOS transistor, and a diode-connected transistor. The second branch coupled to the first branch in a current mirror configuration. A chopper circuit alternately couples drain terminals of the first and second PMOS transistors in series to the remainder of their respective branches.
1. A bandgap reference circuit, comprising:
a complimentary to absolute temperature (CTAT) current generator providing a CTAT current and including a source degeneration resistor;
a proportional to absolute temperature (PTAT) current generator providing a PTAT current and comprising:
a first branch comprising a source degeneration resistor, a first p-type metal-oxide semiconductor (PMOS) transistor, and a first n-type metal oxide semiconductor (NMOS) transistor, a resistor, and a diode-connected transistor;
a second branch comprising a source degeneration resistor, a second PMOS transistor, a second NMOS transistor, and a diode-connected transistor, the second branch coupled to the first branch in a current mirror configuration; and
a chopper circuit alternately coupling drain terminals of the first and second PMOS transistors to the remainder of their respective branches;
a first current mirror coupled to mirror the CTAT current and including a source degeneration resistor;
a second current mirror coupled to mirror the PTAT current and including a source degeneration resistor;
an output configured to combine the mirrored CTAT and PTAT currents to provide a reference current;
a first lowpass filter coupling gates of the first and second PMOS transistors of the PTAT current generator to a gate of a PMOS transistor in the second current mirror; and
a second lowpass filter coupling a gate of a PMOS transistor in the CTAT current generator to a gate of a PMOS transistor of the first current mirror.
2. The bandgap reference circuit of claim 1 , wherein the PTAT current generator further comprises:
a third PMOS transistor in the first branch with a source alternately coupled to the first PMOS transistor in a cascode configuration or to a drain of the second PMOS transistor depending on a phase of the chopper circuit; and
a fourth PMOS transistor in the second branch with a source alternately coupled to the first PMOS transistor in a cascode configuration or to a drain of the second PMOS transistor depending on a phase of the chopper circuit.
3. The bandgap reference circuit of claim 1 , wherein the PTAT current generator further comprises:
a third NMOS transistor with a source alternately coupled to a drain of the first NMOS transistor through a second chopper circuit; and
a fourth NMOS transistor with a source alternately coupled to a drain of the second NMOS transistor through the second chopper circuit,
the second chopper circuit alternately coupling the sources of the third and fourth NMOS transistors to each other.
4. The bandgap reference circuit of claim 1 , further comprising:
and an amplifier configured to couple a voltage of the diode-connected transistor of the second branch to a resistor in the CTAT current generator.
5. The bandgap reference circuit of claim 4 , wherein:
the source degeneration resistor of the first current mirror, the source degeneration resistor of the second current mirror, and the resistor in the CTAT current generator are adjustable to set a temperature coefficient of the reference current.
6. A method for generating a reference current, the method comprising:
generating a proportional-to-absolute-temperature (PTAT) current using first and second branches of a PTAT current generator including source degeneration resistors;
alternately coupling drain terminals of first and second PMOS transistors in the first and second branches to each other and in series to the remainder of their respective branches with a first chopper circuit, each of the first and second PMOS transistors having a respective source degeneration resistor;
generating a complementary-to-absolute-temperature (CTAT) current with a CTAT current generator;
generating a copy of the PTAT current using a PTAT current mirror with source degeneration, the generating including lowpass filtering a signal from gates of the first and second PMOS transistors of the PTAT current generator and feeding it to a gate of a PMOS transistor in the PTAT current mirror;
generating a copy of the CTAT current using a CTAT current mirror with source degeneration, the generating including lowpass filtering signal from a gate of a PMOS transistor in the CTAT current generator and feeding it to a gate of a PMOS transistor in the CTAT current mirror; and
combining the copy of the PTAT current and the copy of the CTAT current to generate the reference current.
7. The method of claim 6 , further comprising:
in the first branch, alternately coupling a drain of an NMOS transistor to a source of another NMOS transistor through a second chopper circuit;
in the second branch, alternately coupling a drain of an NMOS transistor to a source of another NMOS transistor through the second chopper circuit; and
alternately coupling the sources of the NMOS transistors to each other through the second chopper circuit.
8. The method of claim 7 , further comprising:
adjusting a source degeneration resistor of the PTAT current mirror and a source degeneration resistor of the CTAT current mirror to set a temperature coefficient of the reference current.
9. An integrated circuit comprising:
a bandgap reference circuit that is a functional block of the integrated circuit, comprising:
a complimentary to absolute temperature (CTAT) current generator providing a CTAT current and including a source degeneration resistor;
a proportional to absolute temperature (PTAT) current generator providing a PTAT current and comprising:
a first branch comprising a source degeneration resistor, a first p-type metal-oxide semiconductor (PMOS) transistor, and a first n-type metal oxide semiconductor (NMOS) transistor, a resistor, and a diode-connected transistor;
a second branch comprising a source degeneration resistor, a second PMOS transistor, a second NMOS transistor, and a diode-connected transistor, the second branch coupled to the first branch in a current mirror configuration; and
a chopper circuit alternately coupling drain terminals of the first and second PMOS transistors to each other and in series to the remainder of their respective branches;
a first current mirror coupled to mirror the CTAT current and including a source degeneration resistor;
a second current mirror coupled to mirror the PTAT current and including a source degeneration resistor;
an output configured to combine the mirrored CTAT and PTAT currents to provide a reference current;
a first lowpass filter coupling gates of the first and second PMOS transistors of the PTAT current generator to a gate of a PMOS transistor in the second current mirror; and
a second lowpass filter coupling a gate of a PMOS transistor in the CTAT current generator to a gate of a PMOS transistor of the first current mirror.
10. The integrated circuit of claim 9 , wherein the PTAT current generator further comprises:
a third PMOS transistor in the first branch with a source alternately coupled to the first PMOS transistor in a cascode configuration or to a drain of the second PMOS transistor depending on a phase of the chopper circuit; and
a fourth PMOS transistor in the second branch with a source alternately coupled to the first PMOS transistor in a cascode configuration or to a drain of the second PMOS transistor depending on a phase of the chopper circuit.
11. The integrated circuit of claim 9 , wherein the PTAT current generator further comprises:
a third NMOS transistor with a source alternately coupled to a drain of the first NMOS transistor through a second chopper circuit; and
a fourth NMOS transistor with a source alternately coupled to a drain of the second NMOS transistor through the second chopper circuit,
the second chopper circuit alternately coupling the sources of the third and fourth NMOS transistors to each other.