Dual-Slope Temperature Sensor Using PTAT/CTAT Current Ratio
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Solution Overview
Problem
Modern System-on-a-Chips (SoCs) require high temperature resolution on-chip temperature sensors with low power consumption and reduced noise, but existing solutions like sigma-delta converters and decimation filters are bulky and consume significant power and area.
Innovation Solution
A dual-slope analog-to-digital converter (ADC) using complementary-to-absolute-temperature (CTAT) and proportional-to-absolute-temperature (PTAT) currents, combined with dynamic element matching and chopping, to reduce noise and power consumption while maintaining high accuracy and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sigma-delta converter is used as a read-out circuit for high temperature resolution, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent changes the fundamental operating parameters of the temperature sensor by using PTAT and CTAT current sources instead of traditional voltage-based sensing. This current-based approach with dual-slope ADC conversion simplifies the read-out circuitry while maintaining high temperature resolution, directly resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent replaces complex voltage-based signal conditioning and conversion mechanisms with a current-based dual-slope ADC approach. This substitution eliminates the need for bulky operational amplifiers and complex filtering circuits, reducing device complexity while preserving temperature measurement precision
2Measurement precision
If a sigma-delta converter is used as a read-out circuit for high temperature resolution, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent employs periodic dual-slope ADC conversion cycles that integrate temperature-dependent currents over fixed time periods. This periodic integration approach achieves high temperature resolution through time-averaged measurement without requiring continuous high-power operation, thereby reducing overall power consumption while maintaining measurement precision
Solution Approach 2:
The patent extracts and eliminates the power-consuming decimation filter stage from the read-out circuit by using direct dual-slope ADC conversion. This extraction of unnecessary circuit elements significantly reduces power consumption while preserving the high temperature resolution capability through the current-based measurement approach
3Measurement precision
If dynamic element matching and chopping are used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary chopping action to the PTAT and CTAT current sources before they enter the dual-slope ADC. This pre-chopping eliminates low-frequency noise and offset errors at the source, improving temperature reading accuracy without requiring complex post-processing circuits, thus resolving the contradiction between measurement precision and device complexity
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 dual-slope ADC achieves high accuracy and resolution with reduced switching and thermal noise, minimizing power consumption and area, and improves temperature reading accuracy through trimming and averaging.
Implementation Method 1
the first reference current may comprise a complementary-to-absolute-temperature (CTAT) current, and the second reference current comprises a proportional-to-absolute-temperature (PTAT) current
Implementation Method 2
the first reference current may comprise a PTAT current, and the second reference current comprises a CTAT current
Data Source
Figure 1~2
Figure 3A~3b
Figure 4A~4C
AI summary
A temperature sensor and method of temperature sensing is described. A first reference current is provided to a dual-slope ADC during a first slope time duration of a dual-slope ADC conversion cycle. A second reference current is provided to the dual-slope ADC during a second slope time duration of the dual-slope ADC conversion cycle. A digital codeword corresponding to a ratio of the first and second reference currents is then output by the dual-slope ADC. The first and second reference current ratio is related to the temperature.