MOSFET Bandgap Reference Circuit for Sub-1V Temperature Stability
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Solution Overview
Problem
Current bandgap reference voltage circuits face challenges in generating a temperature-independent reference voltage due to the requirement for bipolar junction transistors (BJTs), which become impractical at very low supply voltages below 1 volt.
Innovation Solution
A bandgap reference voltage generator is designed using four transistors (two N-type and two P-type MOSFETs) and several resistors, eliminating the need for BJTs and allowing operation at very low supply voltages. The circuit generates a temperature-independent reference voltage by combining proportional-to-absolute temperature (PTAT) and complementary-to-absolute temperature (CTAT) voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If bipolar junction transistors (BJTs) are used to generate reference voltage, then temperature independence is achieved, but the circuit cannot operate at supply voltages below 1 volt due to the 0.7V base-emitter voltage requirement
Solution Approach 1:
The patent extracts and eliminates the BJT component from the reference voltage generation circuit, replacing it with MOSFETs that have no base-emitter voltage constraint. This allows the circuit to operate at supply voltages below 1 volt while maintaining temperature independence through alternative circuit topology using MOSFET threshold voltage characteristics
Solution Approach 2:
The patent changes the fundamental voltage parameter from BJT base-emitter voltage (0.7V minimum) to MOSFET gate-source voltage, which can operate at lower voltages. By utilizing the threshold voltage characteristics of MOSFETs and configuring the circuit to generate PTAT and CTAT components that combine to a temperature-independent reference, the circuit achieves both low voltage operation and temperature stability
2Area of stationary object
If transistor size is reduced to meet smaller chip dimensions, then area is reduced, but breakdown voltage decreases making low supply voltage operation even more challenging
Solution Approach 1:
The patent employs standard CMOS process MOSFETs with typical threshold voltages rather than requiring high-breakdown-voltage specialized devices. The circuit design accepts the lower voltage tolerance of scaled transistors and compensates through topology, allowing use of commercially available standard-cell library components that are optimized for area efficiency in modern CMOS processes
Solution Approach 2:
The patent designs the circuit to dynamically adapt to the actual transistor characteristics and supply voltage conditions. The MOSFET-based reference circuit can operate across a range of voltages and automatically adjusts its operating point, making it resilient to variations in transistor breakdown voltage due to scaling and process variations
Data Source
AI summary
The present invention provides a bandgap reference voltage generator, which includes a first transistor, a second transistor, a third transistor and a fourth transistor. A source electrode of the first transistor is coupled to a ground voltage via at least a first resistor. A source electrode of the second transistor is coupled to the ground voltage, and a gate electrode of the second transistor is coupled to a gate electrode of the first transistor. The third transistor is coupled between the first resistor and a supply voltage. The fourth transistor is coupled to the second transistor via a second resistor. The bandgap reference voltage generator generates a reference voltage at the drain electrode of fourth transistor; and a size of the first transistor is greater than a size of the second transistor, or a size of the third transistor is smaller than a size of the fourth transistor.