MOSFET Reference Circuit for Temperature Invariant Voltage
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Solution Overview
Problem
Existing bandgap circuits, particularly those based on bipolar junction transistors (BJTs), are not suitable for small, low-cost integrated circuits and face challenges in providing a fixed voltage/current ratio due to temperature variations, while MOSFET-based circuits are complex to trim and require precise temperature-invariant resistors.
Innovation Solution
A reference generation circuit using p-channel metal-oxide-semiconductor FETs (PFETs) with a voltage/current bias circuitry that generates temperature and supply invariant voltage and current outputs, where the magnitude of one current is a predetermined function of another, and the voltage potential at one output is equal to the other, ensuring a cascaded current source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If BJT based bandgap circuits are used, then temperature stability is improved, but device size and cost increase
Solution Approach 1:
The patent substitutes bipolar junction transistors (BJTs) with metal-oxide-semiconductor field-effect transistors (MOSFETs) to achieve temperature compensation. This replacement reduces device size and cost while maintaining the temperature stability function through the different temperature characteristics of MOSFETs compared to BJTs
Solution Approach 2:
The patent changes the fundamental transistor type parameter from BJT to MOSFET, utilizing the distinct temperature coefficients of these devices. By combining MOSFETs with specific resistors, the circuit achieves temperature compensation without requiring large BJT structures
2Stability of the object's composition
If precise temperature-invariant resistors are used, then voltage/current ratio stability is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes from requiring precise temperature-invariant resistors to using standard resistors with known temperature coefficients. By combining these with MOSFETs having opposite temperature characteristics, the circuit achieves ratio stability through parameter compensation rather than requiring expensive precision components
Solution Approach 2:
The patent converts the harmful temperature drift of standard resistors into a beneficial effect by combining it with MOSFETs that exhibit opposite temperature characteristics. The harmful temperature coefficient of the resistor becomes useful for compensating the MOSFET's drift, achieving stability without precision resistors
Data Source
AI summary
A reference circuit constituted of: a voltage/current bias circuitry; a first transistor coupled between a common voltage and an first bias circuitry output; a second transistor coupled between the common voltage and a second bias circuitry output; a third transistor coupled between the common voltage and an output providing a temperature and supply invariant current; a resistor coupled between the second transistor and the second output of the bias circuitry; and an output providing a temperature and supply invariant voltage coupled between the resistor and the second transistor, the voltage output terminal further coupled to a gate of the third transistor, wherein the bias circuitry is arranged, in cooperation with the first transistor, to generate a first current at the first output thereof, and, in cooperation with the second transistor, to generate a second current at the second output thereof, the current magnitudes exhibiting a ratio of a predetermined value.