MOSFET Voltage Reference Circuit for Low-Supply CMOS Stability
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Solution Overview
Problem
Existing voltage reference circuits face challenges in maintaining stability and operation due to variations in manufacturing process, power supply voltage, and temperature, especially when bipolar junction transistors (BJTs) are unavailable or power supply voltage levels are insufficient to properly bias BJTs.
Innovation Solution
The implementation of an asymmetric MOSFET-based differential pair architecture, utilizing MOSFETs with different threshold voltages, allows for the generation of a reference voltage based on the difference between the threshold voltages, enabling operation at power supply voltage levels insufficient for BJT operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bipolar junction transistors (BJTs) are used in voltage reference circuits, then stable reference voltage can be generated based on silicon band gap, but the circuit cannot operate when power supply voltage levels are insufficient to properly bias BJTs
Solution Approach 1:
The patent changes the operating parameters by switching from BJT-based band gap reference to MOSFET-based threshold voltage difference reference. This allows the circuit to operate at lower power supply voltages (below 1.25V) where BJTs cannot be properly biased, while still providing a stable reference voltage that is independent of power supply variations.
Solution Approach 2:
The patent substitutes the physical mechanism for generating reference voltage: replacing the silicon band gap physical effect (used in BJTs) with the difference in threshold voltages between MOSFETs. This substitution enables operation in voltage regimes where the original mechanism (BJT band gap) cannot function.
2Reliability
If conventional band gap reference circuits are used, then reference voltage stability is achieved, but the circuits are not available in pure CMOS processes without explicit BJTs
Solution Approach 1:
The patent replaces the BJT-based band gap reference mechanism with a MOSFET-based threshold voltage difference mechanism. This substitution makes the reference circuit compatible with pure CMOS manufacturing processes that do not include explicit BJTs, while maintaining the ability to generate a stable reference voltage through the MOSFET threshold voltage characteristics.
3Adaptability or versatility
If MOSFETs with different threshold voltages are used, then operation at low power supply voltage levels is enabled, but the circuit complexity increases due to asymmetric differential pair architecture
Solution Approach 1:
The patent deliberately introduces asymmetry by using MOSFETs with different threshold voltages in the differential pair configuration. This asymmetric design enables the circuit to generate a reference voltage based on the threshold voltage difference, allowing operation at low power supply voltage levels (below 1.25V) where symmetric designs would fail to properly bias the transistors.
Data Source
AI summary
A voltage reference circuit included in a computer system includes an asymmetric amplifier circuit that includes two metal-oxide semiconductor field-effect transistors with different threshold voltages. The voltage reference circuit also includes an output circuit that generates, using a control signal, a bias signal and an output current that is used by a divider circuit to generate a reference voltage and a feedback voltage. The reference voltage and bias signal are used by the amplifier circuit to generate the control signal, which is based on a difference between the transistors' threshold voltages.