Die Temperature Sensor Circuit Using Bipolar Transistors
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Solution Overview
Problem
Existing die temperature sensor circuits face significant errors due to input offset voltages from MOS operational amplifiers and require large die area, leading to inaccuracies in temperature measurement, particularly because of non-linear temperature dependencies and mismatched resistive elements.
Innovation Solution
A die temperature sensor circuit utilizing bipolar transistors as both inputs and amplifiers, with a dual-function input differential pair that generates a PTAT input offset voltage, reducing the need for MOS transistors and minimizing errors through a feedback structure with specific ratios of resistive elements, thereby achieving higher accuracy and reduced die area usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If three MOS operational amplifiers are used to amplify the temperature signal, then the signal amplification is achieved, but the input offset voltage errors are multiplied and added, significantly degrading measurement precision
Solution Approach 1:
The patent extracts and eliminates the harmful input offset voltage errors by using bipolar transistors instead of MOS transistors for the input differential pair. Bipolar transistors inherently have much lower input offset voltages, thereby removing the primary source of measurement error while maintaining signal amplification capability through the same operational amplifier structure.
Solution Approach 2:
The patent changes the transistor type parameter from MOS to bipolar for the input differential pair. This parameter change fundamentally alters the electrical characteristics, particularly the input offset voltage, which is significantly lower in bipolar transistors. This enables accurate temperature measurement without the error multiplication problem inherent in MOS-based operational amplifiers.
2Ease of manufacture
If MOS operational amplifiers with MOS transistor input differential pairs are used, then the circuit implementation is simplified, but input offset voltage errors are introduced and amplified, creating non-PTAT errors that cannot be corrected by linear calibration
Solution Approach 1:
The patent converts the inherent characteristics of bipolar transistors into a benefit by utilizing their low input offset voltage property. While bipolar transistors require slightly more complex biasing, their natural tendency to have minimal offset voltage transforms what could be a manufacturing complexity into a significant advantage for measurement precision, eliminating the need for complex error correction circuits.
3Measurement precision
If unitary resistors are used to implement resistive elements with precise ratios, then the gain accuracy is improved, but manufacturing complexity and die area increase due to the need for multiple precisely matched resistors
Solution Approach 1:
The patent merges multiple resistive elements into fewer physical components by using a single resistive element for both feedback and gain setting functions. The feedback resistor and the resistor setting the gain ratio are combined into one physical resistor, eliminating the need for multiple precisely matched resistors while maintaining accurate gain control through the operational amplifier's feedback mechanism.
4Power
If three operational amplifiers are used in the temperature sensor circuit, then the temperature signal can be properly amplified and buffered, but the die area required is large
Solution Approach 1:
The patent makes the single operational amplifier multi-functional by using it simultaneously for signal amplification, buffering, and gain control. The operational amplifier serves multiple purposes in the circuit: it amplifies the differential voltage from the bipolar transistors, buffers the output signal, and its feedback network provides precise gain control. This eliminates the need for separate buffer amplifiers, significantly reducing die area while maintaining full signal processing capability.
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 provides improved accuracy and reduced power consumption by eliminating input offset voltage errors and minimizing die area, achieving a thermal coefficient of about 5 mV/K and achieving one-degree accuracy, which is significantly better than existing technologies.
Implementation Method 1
A difference between a base-to-emitter voltage of bipolar transistor 101 and a base-to-emitter voltage of bipolar transistor 102, or ΔVBE, is PTAT
Data Source
AI summary
A die temperature sensor circuit (200) includes an amplifier (203) that has first and second stages of amplification and that has bipolar transistors (201 and 202) as an input differential pair. The bipolar transistors have different current densities. A difference between base-emitter voltages of the bipolar transistors is proportional to absolute temperature of the bipolar transistors. The bipolar transistors also provide amplification for the first stage of amplification. Multiple feedback loops maintain a same ratio between the current densities of the bipolar transistors over temperature by changing collector currents that bias the bipolar transistors. A feedback loop includes a second stage of amplification and such feedback loop cancels effect that base currents of the bipolar transistors have on an output signal of the die temperature sensor circuit.