Low Voltage Reference Circuit Using Differential Transistors
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Solution Overview
Problem
Existing reference voltage generation methods in integrated circuits suffer from inaccuracy due to manufacturing process, operational voltage, and temperature variations, especially when the supply voltage is low, such as 0.9 V or less, and are not viable for generating reference voltages below 0.8 V.
Innovation Solution
A circuit comprising NMOS and PMOS transistors, amplifiers, and resistors is used to generate a reference voltage that is independent of manufacturing process, operational voltage, and temperature variations, utilizing a differential pair of NMOS transistors with zero bulk-source voltage and PMOS transistors as diodes, along with resistors and capacitors to filter noise and stabilize the voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bandgap generator is used to generate reference voltage, then reference voltage can be generated, but the accuracy is limited to about 3% and it is not viable for supply voltages of 0.9V or less
Solution Approach 1:
The patent changes the operating parameters by using MOSFETs in the sub-threshold region instead of the traditional strong inversion region, and operates the bandgap generator at supply voltages of 0.9V or less. This parameter change enables reference voltage generation in low-voltage applications while achieving better than 3% accuracy through the exponential relationship in the sub-threshold region that provides temperature compensation.
2Use of energy by moving object
If MOSFET operates in sub-threshold region to generate reference voltage, then low supply voltage operation is enabled, but inaccuracy occurs due to process variations especially when polysilicon resistor is involved
Solution Approach 1:
The patent employs feedback mechanisms through the differential pair configuration and operational amplifiers that continuously monitor and adjust the reference voltage. The feedback loop compensates for process variations by detecting deviations and correcting them, thereby maintaining accuracy despite operating in the sub-threshold region with polysilicon resistors.
Solution Approach 2:
The patent uses matched pairs of MOSFETs and resistors where one pair operates in a different region or has different dimensions but is designed to replicate the electrical characteristics of the other. This copying approach with careful matching allows the circuit to cancel out process variations through differential operation.
3Power
If different threshold voltage transistors are used, then voltage difference can be generated, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by using transistors with different threshold voltages in specific locations within the differential pair configuration. Each transistor is optimized for its specific function - one with lower threshold voltage for better sub-threshold operation and another with higher threshold voltage for stability. The local optimization of each transistor's threshold voltage allows the generation of the required voltage difference while managing manufacturing precision requirements through the differential architecture.
Data Source
AI summary
A circuit comprises a first amplifier and a second amplifier. The first amplifier is configured to amplify a first voltage difference between a first voltage and a second voltage, and to generate a third voltage. The second amplifier is configured to amplify a second voltage difference between the third voltage and an input voltage, and to generate an output voltage. The first voltage is a voltage at a first terminal of a first transistor. The second voltage is a voltage at a second terminal of a second transistor. A first gate of the first transistor is adapted to receive the third voltage. A second gate of the second transistor is adapted to receive the input voltage. Threshold voltage values of the first transistor and the second transistor differ.