Curvature Compensated Band-Gap Reference Circuit Trimming
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Solution Overview
Problem
Band-gap voltage reference circuits face challenges in minimizing temperature-dependent variations, particularly when used as peripheral elements in integrated circuits, where process limitations and shared substrates lead to significant temperature-related errors and curvature issues, affecting accuracy and reliability.
Innovation Solution
A circuit design that incorporates a PTAT current source, op-amps, and resistive voltage dividers with a trimmable element, allowing for curvature compensation and temperature trimming at a single temperature, reducing the number of op-amps and current mirrors, and making the design less susceptible to process variations and resistor absolute values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional band-gap circuits are used to provide reference voltage, then temperature independent reference can be achieved, but process limitations and shared substrate lead to significant temperature-related errors and curvature issues
Solution Approach 1:
The patent segments the temperature compensation function into multiple distinct circuits: a first temperature compensation circuit that compensates for first-order temperature effects, and a second temperature compensation circuit that compensates for curvature (second-order) temperature effects. This segmentation allows each circuit to be optimized independently for its specific compensation function, improving overall accuracy while addressing the manufacturing precision limitations.
Solution Approach 2:
The patent introduces intermediate compensation nodes and auxiliary circuits that mediate between the PTAT current source and the final reference voltage output. These intermediary elements include compensation capacitors and additional transistors that facilitate gradual temperature effect cancellation, allowing the circuit to achieve better curvature accuracy despite process variations.
2Measurement precision
If multiple op-amps and current mirrors are used to compensate for temperature effects, then temperature accuracy improves, but device complexity increases
Solution Approach 1:
The patent merges the temperature compensation function with the reference voltage generation function into an integrated circuit architecture. The temperature compensation circuits are combined with the band-gap reference core, allowing multiple functions to be achieved with shared components. This merging reduces the total number of discrete op-amps and current mirrors compared to separate compensation stages.
Solution Approach 2:
The patent designs op-amps and transistors to serve multiple functions simultaneously. For example, certain transistors participate in both the PTAT current generation and the temperature compensation processes. This multi-functionality reduces the overall component count while maintaining the required temperature accuracy.
3Reliability
If band-gap circuits are designed for high accuracy, then temperature variations are minimized, but the circuit occupies larger area and shares substrate with other circuits
Solution Approach 1:
The patent employs dynamic temperature compensation techniques where compensation capacitors are charged and discharged in controlled stages. This dynamic approach allows the circuit to achieve accurate temperature compensation without requiring all compensation components to be present simultaneously, effectively reducing the occupied area while maintaining temperature stability.
Solution Approach 2:
The patent nests compensation functions within the existing band-gap reference structure. The temperature compensation circuits are embedded within the reference voltage generation circuitry, with compensation nodes integrated into the signal path. This nesting allows multiple functions to share the same substrate area, reducing the overall circuit footprint while maintaining high temperature stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively cancels out band-gap curvature, achieving a stable reference voltage with minimal temperature variation, enabling accurate voltage generation for applications like non-volatile memory and high voltage biases, while allowing trimming at a single temperature, thus reducing manufacturing costs and improving circuit reliability.
Implementation Method 1
The band-gap voltage reference is generated by the combination of a Proportional to Absolute Temperature (PTAT) element and a Complementary to Absolute Temperature (CTAT) element. The voltage difference between two diodes is used to generate a PTAT current in a first resistor.
Implementation Method 2
The PTAT current typically is used to generate a voltage in a second resistor, which is then added to the voltage of one of the diodes. The voltage across a diode operated with the PTAT current is the CTAT element that decreases with increasing temperature.
Data Source
AI summary
A band-gap reference circuit is compensated for temperature dependent curvature in its output. A voltage across a diode with a fixed current is subtracted from a voltage across a diode with a proportional to absolute temperature (PTAT) current. The resultant voltage is then magnified and added to a PTAT voltage and a diode's voltage that has a complementary-to-absolute temperature (CTAT) characteristic, resulting in a curvature corrected hand-gap voltage. This allows for the band-gap reference circuit to be trimmed at a single temperature. This allows the circuit to be made with only a single trimmable parameter, which, in the exemplary circuits, is a resistance value.