Diode Temperature Sensor Feedback Loop for Low-Noise PTAT Sensing
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Solution Overview
Problem
Existing CMOS temperature sensor semiconductor devices face challenges in reducing chip area and power consumption while maintaining high accuracy, particularly in resolving low voltage differences and dealing with mismatch errors and noise.
Innovation Solution
The proposed temperature sensor semiconductor device incorporates a SAR feedback loop with dynamically matched current sources, a CTAT voltage generator, and an open-loop transconductance/capacitance stage, which eliminates noise and settling tradeoffs, and employs dynamic element matching to filter DEM ripple and boost PTAT voltage, thereby reducing chip area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a PTAT generator with bipolar transistors and feedback loop is used to achieve high temperature sensing accuracy, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent changes the fundamental operating parameters by using CMOS transistors instead of bipolar transistors, operating in strong inversion region with specific W/L ratios to achieve PTAT voltage generation without requiring complex bipolar junction structures or feedback loops. This parameter change simplifies the device while maintaining measurement precision.
Solution Approach 2:
The patent extracts and eliminates the feedback loop component from the temperature sensing circuitry. By using directly proportional CMOS transistor characteristics, the PTAT voltage is generated inherently without requiring feedback mechanisms, thereby reducing device complexity while preserving accuracy.
2Measurement precision
If chopping and dynamic element matching are employed to reduce noise and mismatch errors, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent employs self-service by utilizing the inherent symmetrical characteristics of the CMOS transistor pair and natural cancellation of mismatch errors through balanced circuit design. The circuit self-corrects for process variations without requiring external dynamic element matching mechanisms, thereby reducing power consumption while maintaining precision.
3Device complexity
If voltage-to-current conversion is performed for PTAT and CTAT voltages in a current domain ADC, then device complexity is reduced, but additional errors are introduced and power consumption increases
Solution Approach 1:
The patent applies multi-functionality by designing the CMOS transistor circuit to simultaneously perform temperature sensing, PTAT voltage generation, and direct digital conversion without requiring separate voltage-to-current conversion stages. The same transistor pair serves multiple functions, reducing overall device complexity while avoiding additional conversion errors.
4Device complexity
If the ratio of PTAT and CTAT voltages depends on resistor matching, then device complexity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent substitutes mechanical/resistive elements with field-effect transistor characteristics. Instead of relying on resistor matching ratios, the circuit uses the electrical characteristics of CMOS transistors in strong inversion, which can be more precisely controlled and matched through standard CMOS fabrication processes, thereby reducing manufacturing precision requirements.
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
This solution enables faster conversion times and improved accuracy with reduced noise and mismatch errors, allowing for precise temperature sensing with lower power consumption and smaller chip area, suitable for portable and medical devices.
Implementation Method 1
A silicon bandgap temperature sensor makes use of the fact that the forward voltage of a silicon diode, especially the base-emitter junction of a bipolar transistor, depends on temperature. The voltage difference between two pn junctions, operated at different current densities, is proportional to absolute temperature (PTAT). The voltage across a pn junction operated with a current that is generated with a PTAT voltage is complementary to absolute temperature (CTAT).
Data Source
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AI summary
The temperature sensor comprises first and second diodes (bip1, bip2) of specified ratio, the first diode (bip1) being connected between a negative supply voltage and a first resistor (R1) provided for a PTAT voltage (Vptat) drop, an array of dynamically matched current sources employing a dynamic element matching controller (DEM), the first resistor being connected between the first diode and a first input of the array, the second diode (bip2) being connected between the negative supply voltage and a second input of the array, and a SAR feedback loop, which comprises a SAR controller, a SAR comparator, a generator for a CTAT voltage (Vctat), and an adjustable second resistor (R2), which implements a DAC and converts the CTAT voltage into a proportional current. The generator for the CTAT voltage is connected to the array of current sources to define a nominal current.