Resistor-less Amplifier Circuit for Low Power Bandgap Reference
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Solution Overview
Problem
Low-power bandgap voltage reference circuits face challenges in amplifying small signals while maintaining low power consumption and area efficiency, as high ohmic value resistors occupy large areas and MOS transistor-based circuits lack linearity and accuracy due to error sources and fabrication process variations.
Innovation Solution
The use of compact structures comprising metal-oxide-semiconductor (MOS) transistors and bipolar junction transistors (BJTs) in a closed-loop feedback system to amplify small magnitude signals, where BJTs produce a proportional-to-absolute-temperature (PTAT) voltage and MOS transistors replicate the signal accurately without resistors, allowing for cascaded cells to build an amplified output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high ohmic value resistors are used to maintain low currents in low-power circuits, then power consumption is reduced, but area occupied by resistors increases significantly
Solution Approach 1:
The patent removes resistors from the circuit topology entirely, extracting the harmful element that causes the area problem. The amplifier circuit uses only MOS transistors configured in differential pairs and current mirrors, eliminating the need for high-value resistors while maintaining low-power operation through controlled current sources.
Solution Approach 2:
The patent substitutes the passive resistor-based current limiting approach with an active MOS transistor-based current mirror system. This replacement allows precise current control without requiring large physical resistors, achieving the same current limitation function through transistor gate control rather than ohmic resistance.
2Area of moving object
If MOS transistors are used instead of resistors to reduce area, then area is reduced, but linearity and accuracy deteriorate due to second-order effects and fabrication variations
Solution Approach 1:
The patent implements a feedback mechanism where the differential amplifier output controls current mirrors that regulate the operating points of the MOS transistors. This feedback loop compensates for second-order effects and fabrication variations, maintaining linearity and accuracy despite using MOS transistors instead of resistors.
Solution Approach 2:
The patent changes the operating parameters of the MOS transistors dynamically through the feedback control system. By adjusting gate voltages and current levels based on output conditions, the circuit maintains optimal linearity and accuracy across varying conditions, compensating for device variations without requiring resistors.
3Measurement precision
If conventional resistor-based circuits are used for signal amplification, then linearity and accuracy are improved, but power consumption increases
Solution Approach 1:
The patent employs dynamic biasing through current mirrors controlled by the differential amplifier output. This dynamic control allows the circuit to maintain high linearity and accuracy similar to resistor-based circuits while consuming less power by adjusting current levels adaptively rather than using fixed high-value resistors that require higher voltage drops.
4Use of energy by moving object
If high-value resistors are used to limit current to nanoamps, then power consumption is reduced, but the voltage drop across resistors requires very high ohmic values, increasing area
Solution Approach 1:
The patent replaces the passive ohmic current limiting mechanism with an active transistor-based current control system. Instead of relying on high-value resistors to naturally limit current, the circuit uses MOS transistors in current mirror configurations that actively regulate current flow, achieving nanoamp-level currents without requiring extreme resistor values.
Data Source
AI summary
A resistor-less amplifying circuit includes a plurality of resistor-less cells. Each cell includes a plurality of MOS transistors. Each cell generates a differential output equal to ΔVGS of two MOS transistors with a magnitude of the differential output controlled by a control voltage generated by a differential amplifier coupled to a feedback loop around a cell. In one embodiment, the resistor-less amplifying circuit is a part of a bandgap voltage reference circuit. In another embodiment, the resistor-less amplifying circuit is part of a temperature sensor circuit.