Remote-Junction Temperature Sensing With Resistance and Offset Cancellation
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Solution Overview
Problem
Bipolar junction transistor (BJT) temperature sensors face accuracy issues due to series resistance errors, especially in remote sensing applications, where the length of connecting wires introduces significant error terms in the measurement of voltage differences across the base-emitter junction.
Innovation Solution
The method involves using a delta-sigma analog-to-digital converter to measure voltage differences at different bias current ratios, canceling series resistance errors by integrating and processing the voltage measurements in a specific sequence, and employing a dummy calibration cycle to account for offset errors, thereby eliminating the need for additional gain scaling or input polarity reversal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional VBE measurement method is used, then temperature sensing function is achieved, but series resistance errors reduce measurement accuracy
Solution Approach 1:
The patent performs preliminary calibration by measuring the voltage drop across the series resistance at a known reference temperature. This预先 obtained resistance value is then used to compensate for series resistance effects during subsequent temperature measurements, eliminating the need for complex real-time correction circuits.
Solution Approach 2:
The patent replaces complex analog compensation circuits with digital signal processing. By using a delta-sigma ADC to oversample and digitally process the VBE measurements, the system achieves series resistance cancellation through computational algorithms rather than additional analog components.
2Adaptability or versatility
If remote sensing configuration is used, then spatial flexibility is improved, but series resistance and offset errors increase
Solution Approach 1:
The patent combines multiple measurement techniques into a unified approach: it integrates the traditional VBE temperature sensing method with dummy transistor offset cancellation and series resistance compensation. By merging these functions into a single integrated circuit and processing algorithm, it achieves high accuracy in remote sensing without requiring separate compensation circuits.
Solution Approach 2:
The patent introduces a dummy calibration transistor as an intermediary element that experiences the same series resistance and offset effects as the sensing transistor. By measuring the dummy transistor's characteristics and using this data to correct the sensing transistor measurements, the system eliminates the impact of remote sensing errors.
3Measurement precision
If high-resolution ADC is used, then measurement precision is improved, but power consumption and area increase
Solution Approach 1:
The patent employs periodic switching of bias currents through the BJT during the ADC conversion process. By alternating between different current levels in a controlled sequence, the system enables the delta-sigma ADC to achieve high-resolution measurements while maintaining lower average power consumption compared to continuous high-current operation.
Solution Approach 2:
The patent dynamically changes the bias current parameters during measurement based on the conversion stage. The delta-sigma ADC uses variable current levels rather than a fixed current, adjusting the amplitude and timing of current pulses to optimize both measurement resolution and power consumption according to the specific measurement 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 approach enhances the accuracy of temperature measurements by removing series resistance errors, reducing the complexity and power consumption of the system, and allowing for more efficient signal processing, with demonstrated area and power reductions of 18% and 70% respectively.
Implementation Method 1
Because of the known temperature and current dependence of the forward-biased base-emitter junction voltage (VBE), the BJT can be used to measure temperature by subtracting two VBE voltages at two different bias currents in a known ratio.
Data Source
AI summary
A temperature sensor uses a semiconductor device that has a known voltage drop characteristic that is proportional to absolute temperature (PTAT). A controllable current source is coupled to the semiconductor device and is operable to sequentially inject a bias current having a value I(bias) and fixed ratio N of I(bias) into the semiconductor device. A delta sigma analog to digital converter (ADC) has an input coupled to the semiconductor device. The delta sigma ADC is configured to sample and integrate a sequence of voltages pairs produced across the semiconductor device by repeatedly injecting an ordered sequence of selected bias currents into the semiconductor device. The ordered sequence of selected bias currents comprises M repetitions of (N×I(bias); I(bias)) and one repetition of (M×I(bias); M×N×I(bias)).