Switched-Capacitor Bandgap Reference for FinFET Temperature Sensing
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Solution Overview
Problem
Conventional bandgap references and thermal sensors face challenges in scalability, accuracy, and power efficiency, especially in FinFET technologies, due to limitations in current ratios, sensitivity to offset and mismatch errors, and poor quality of PNP components, which hinders their performance in low-power applications like wearables and IoT devices.
Innovation Solution
A digital bandgap reference circuit using capacitive biasing and switched capacitor techniques, which eliminates the need for resistors and amplifiers, allowing for precise current density control and large current ratios, and a thermal sensor design utilizing an N-well-to-substrate junction for robust temperature sensing with reduced complexity and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional bandgap references use analog components (amplifiers, MOS current sources, current mirrors, resistors), then certain performance for accuracy is achieved, but these components are difficult to implement in digital process and do not scale well with future nodes
Solution Approach 1:
The patent replaces traditional analog components (amplifiers, MOS current sources, current mirrors, resistors) with a digital-friendly switched capacitor circuit implementation. The bandgap reference is generated using capacitive switching techniques that are compatible with digital CMOS processes, eliminating the need for complex analog components that are difficult to manufacture in digital processes.
Solution Approach 2:
The patent changes the operating parameters by using switched capacitor techniques with precise timing control instead of continuous analog signals. This allows the bandgap reference to be generated through digital-compatible switching operations rather than traditional analog component relationships, enabling better scaling with future digital process nodes.
2Measurement precision
If BJT current ratios are limited to N=8...20, then a small PTAT-voltage is generated, but the circuit becomes sensitive to offset and mismatch errors
Solution Approach 1:
The patent uses dynamic switched capacitor switching sequences to generate the bandgap reference voltage. By controlling the timing and duration of capacitor charging and discharging phases, the circuit can achieve precise voltage generation without relying on fixed BJT current ratios, thereby reducing sensitivity to offset and mismatch errors while maintaining accurate PTAT-voltage generation.
3Measurement precision
If conventional thermal sensors use parasitic PNP components, then temperature sensing is achieved, but the quality of PNP components degrades drastically due to micro-defects in junctions
Solution Approach 1:
The patent extracts the temperature sensing function from the degraded parasitic PNP components and implements it using a switched capacitor circuit that measures temperature through capacitive voltage decay. This approach removes the dependency on poor-quality PNP junctions while maintaining temperature sensing capability through an alternative mechanism based on capacitor discharge characteristics.
4Measurement precision
If conventional thermal sensors require multi-point trim for sensing adjustment, then measurement accuracy is met, but area and power consumption increase
Solution Approach 1:
The switched capacitor temperature sensor achieves self-calibration through its inherent capacitive voltage decay characteristics. The circuit automatically determines temperature based on the time constant of capacitor discharge through the diode, eliminating the need for external multi-point trimming adjustments. This self-service mechanism maintains measurement accuracy without requiring complex trimming circuitry or procedures.
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 enables highly accurate, scalable, and low-power thermal sensing with reduced area and complexity, achieving precise temperature measurements with minimal trimming requirements, suitable for IoT and wearable devices.
Implementation Method 1
capacitive bias is applied to a single n well-diode, which allows determining the current density precisely by pure timing control
Implementation Method 2
a single n well-diode, which is usually of high quality, is used
Data Source
AI summary
An apparatus is provided which generates a reverse bandgap reference using capacitive bias, which is applied to a single n-well diode. The capacitive bias allows for determining the current density precisely by pure timing control. An apparatus is also described for sensing temperature in which a forward-bias diode voltage can be sampled with a capacitor, and large current ratios are possible (e.g., ratio N greater than 1000). Duty cycle of a digital output of the sensor is used to determine the temperature sensed by the sensor.