Low power Bandgap reference circuit with increased accuracy and reduced area consumption
Bandgap reference (BGR) circuits and methods are described herein for providing high accuracy, low power Bandgap operation when using small, low voltage devices in the analog blocks of the BGR circuit. In some cases, chopped input stabilization and dynamic current matching techniques may be combined to compensate for input voltage offsets in the operational amplifier portion and current offsets in the current mirror portion of the Bandgap circuit. When used together, the chopped stabilization and dynamic current matching techniques provide a significant increase in accuracy, especially when using small, low voltage devices in the analog blocks to reduce layout area and support low power supply operation (e.g., power supply values down to about 1.4 volts and below).
1. A Bandgap reference (BGR) circuit configured for reducing mismatch-induced voltage and current offsets within the BGR circuit, the BGR circuit comprising:
an operational amplifier having a pair of chopped stabilization input circuits for reducing a voltage offset attributed to the operational amplifier;
three current mirror devices coupled for receiving an output of the operational amplifier and configured for generating three substantially identical currents therefrom;
three sets of dynamically controlled switches, wherein each set of switches is coupled for receiving a different one of the three substantially identical currents; and
digital control logic configured for reducing a current offset attributed to the current mirror devices by controlling the three sets of switches, so that:
only one switch in each set of switches is activated for conducting current during a first phase of a multi-phase clocking signal; and
only one of the switches activated during the first phase remains activated during each consecutive phase of the multi-phase clocking signal.
2. The Bandgap reference circuit as recited in claim 1 , wherein the three current mirror devices comprise three pairs of low-voltage cascoded devices.
3. The Bandgap reference circuit as recited in claim 1 , wherein the three sets of dynamically controlled switches comprises three sets of three parallel-coupled switches.
4. The Bandgap reference circuit as recited in claim 1 , wherein the digital control logic is coupled for receiving a clocking signal and configured for generating a plurality of control signals in response thereto.
5. The Bandgap reference circuit as recited in claim 4 , wherein the digital control logic is configured for generating a first subset of the control signals by dividing the clocking signal in half to generate two equal-length phases of a second clocking signal, which is supplied to the operational amplifier and to the pair of chopped stabilization input circuits for modulating the output of the operational amplifier.
6. The Bandgap reference circuit as recited in claim 5 , wherein if mismatched-induced voltage offsets occur within the output of the operational amplifier, the first subset of control signals enables a positive voltage offset to be generated during one clock phase and an equally negative voltage offset to be generated during a next clock phase of the second clocking signal.
7. The Bandgap reference circuit as recited in claim 6 wherein the digital control logic, the operational amplifier and the pair of chopped stabilization input circuits are configured for reducing mismatch-induced voltage offsets attributed to the operational amplifier by averaging out the positive and negative voltage offsets generated over two consecutive clock phases of the second clocking signal.
8. The Bandgap reference circuit as recited in claim 5 , wherein the digital control logic is configured for using one of the first subset of control signals to generate a second subset of control signals by dividing one phase of the second clocking signal by six to generate six equal-length phases of a third clocking signal, which is supplied to the three sets of dynamically controlled switches as the multi-phase clocking signal.
9. The Bandgap reference circuit as recited in claim 8 , wherein the digital control logic and the three sets of dynamically controlled switches are configured to eliminate any mismatch-induced current offsets existing between the three current mirror devices by averaging the three substantially identical currents during each phase of the third clocking signal.
10. The Bandgap reference circuit as recited in claim 1 , wherein the three sets of dynamically controlled switches are implemented with high voltage devices to increase the accuracy of the BGR circuit.
11. The Bandgap reference circuit as recited in claim 1 , wherein all transistors within the BGR circuit, except for the three sets of dynamically controlled switches, are implemented with low voltage devices to enable the BGR circuit to remain operational under power supply conditions of about 1.6 volts and below.
12. A current adding Bandgap reference (BGR) circuit configured for generating a stable reference voltage across a specified range of process, voltage and temperature values, the BGR circuit comprising:
a plurality of diodes coupled for producing a proportional to absolute temperature (PTAT) current and a complementary to absolute temperature (CTAT) current;
an operational amplifier coupled for receiving the PTAT and CTAT currents and configured for generating a difference signal therefrom;
three current mirror devices coupled for receiving the difference signal and configured for generating three substantially identical currents therefrom;
three sets of switches, wherein each set of switches is coupled for receiving a different one of the three substantially identical currents;
digital control logic configured for averaging the three substantially identical currents over consecutive phases of a multi-phase clocking signal by controlling the three sets of switches, so that;
only one switch in each set of switches is activated for conducting current during a first phase of the multi-phase clocking signal; and
only one of the switches activated during the first phase remains activated during a consecutive phase of the multi-phase clocking signal; and
at least one resistor coupled to the three sets of switches for receiving the averaged current and configured for developing the stable reference voltage thereacross.
13. The current adding BGR circuit as recited in claim 12 , wherein the three current mirror devices comprise three pairs of low-voltage cascoded devices, and wherein the three sets of switches comprise three sets of three parallel-coupled switches.
14. The current adding BGR circuit as recited in claim 12 , wherein the digital control logic is configured for receiving a first clocking signal and for generating:
a first subset of the control signals, which are supplied to the operational amplifier for reducing mismatch-induced voltage offsets attributed to the operational amplifier by modulating the difference signal with a second clocking signal, whose duty cycle is about 50% that of the first clocking signal; and
a second subset of the control signals generated by dividing one phase of the second clocking signal into six distinct phases of a third clocking signal, wherein the second subset of the control signals is supplied to the three sets of switches for reducing mismatch-induced current offsets attributed to the current mirror devices by controlling the activation of switches, such that only one switch in each set of switches is activated for conducting current during each distinct clock phase of the third clock signal.
15. The current adding BGR circuit as recited in claim 14 , wherein the operational amplifier comprises a pair of chopped stabilization input circuits for receiving the first subset of control signals, and in response thereto, generating a positive voltage offset and an equally negative voltage offset during two consecutive phases of the second clocking signal.