Temperature Sensor Compensation Circuit Design
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Solution Overview
Problem
Temperature sensors based on transistors face inaccuracies due to varying ambient temperatures, causing discrepancies between displayed and actual temperatures due to changes in current flow through the sensor components.
Innovation Solution
A temperature sensor system that includes a temperature sensing core, an analog-to-digital converter, and a temperature compensating circuit generating a counter clock signal with a frequency that varies according to temperature changes, allowing for accurate temperature compensation by adjusting the counter's operating speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional temperature sensor using a bipolar transistor and current mirror is used, then the temperature can be detected by measuring current variation, but the measurement precision deteriorates due to temperature-dependent current changes in all transistor components
Solution Approach 1:
The patent changes the operating parameters of the transistors by applying different bias currents to the bipolar transistor and compensation transistors. By controlling the current ratios and operating points, the patent compensates for temperature-dependent parameter changes in the transistor characteristics, thereby maintaining measurement accuracy across varying temperatures.
Solution Approach 2:
The patent implements a feedback mechanism where the voltage drop across a sensing resistor is used to control the current in compensation transistors. This feedback loop adjusts the compensation current based on the actual temperature-induced changes, counteracting the unwanted current variations and stabilizing the output characteristic.
2Measurement precision
If the ambient temperature increases, then the electron mobility decreases causing current flow to decrease, but this leads to non-linear temperature display and increased measurement error
Solution Approach 1:
The patent converts the harmful temperature-dependent current degradation into a beneficial compensation mechanism. By intentionally designing the compensation circuit to mirror the same physical effects (electron mobility changes), the patent uses these changes to counterbalance the degradation in the sensing transistor, thereby converting the harmful effect into a corrective action.
Solution Approach 2:
The patent introduces compensation transistors that generate opposing current changes to counterbalance the unwanted current variations in the sensing transistor. These compensation currents act as an electrical 'anti-weight' that offsets the negative effects of temperature-induced mobility changes, maintaining overall current characteristic consistency.
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 system significantly reduces temperature measurement errors, achieving a maximum difference of 2°C between actual and displayed temperatures, compared to 23°C in conventional sensors, with improved resolution and reduced area occupancy.
Implementation Method 1
the amount of current flowing through a transistor, which is a semiconductor device, varies according to an ambient temperature around the transistor since electron mobility varies with temperature
Data Source
AI summary
Described is a method and apparatus for compensating for a change in an output characteristic of a temperature sensor due to varying temperature. The temperature sensor includes a temperature sensing core, an analog-to-digital converter, a counter, and a temperature compensating circuit. The temperature sensing core generates a sense voltage corresponding to a sensed temperature. The analog-to-digital converter converts the sense voltage into a digital signal and generates a conversion signal. The temperature compensating circuit generates a counter clock signal that varies according to a temperature change. The counter counts the number of pulses of the counter clock signal according to the conversion signal.