Temperature Sensor Circuit Offset Reduction
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Solution Overview
Problem
Existing temperature sensor circuits in semiconductor integrated circuits, particularly those using CMOS processes, face limitations in setting arbitrary temperature gradients and are prone to significant input offset variations, which restrict their usability and require additional trimming circuits.
Innovation Solution
A temperature sensor circuit design that utilizes npn type bipolar transistors with varying emitter current densities and resistors to generate a temperature sense signal resistant to offset, allowing for arbitrary temperature gradient settings through resistance ratio adjustments, effectively canceling temperature dependence and reducing offset voltage influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a temperature sensor circuit is mounted in a CMOS integrated circuit, then the circuit can be integrated into standard CMOS processes, but the input offset of the operational amplifier varies greatly requiring additional trimming circuits
Solution Approach 1:
The patent extracts the temperature sensing function from the operational amplifier's input stage by using a dedicated temperature sensor circuit that generates a temperature sense signal. This separate temperature sensing path avoids the offset voltage issues inherent in CMOS operational amplifiers, as the temperature measurement is performed independently through a bipolar transistor-based sensing mechanism rather than relying on the CMOS amplifier's input characteristics.
Solution Approach 2:
The patent introduces a temperature sense signal as an intermediary between the temperature physical quantity and the digital output. This temperature sense signal, generated by the bipolar transistor circuit, serves as a stable intermediate representation that is then processed by the operational amplifier. The bipolar transistor acts as an intermediary element that converts temperature into a voltage signal with predictable temperature dependence, bypassing the offset issues of the CMOS amplifier.
2Measurement precision
If a reference voltage circuit is designed to have no temperature dependence, then temperature measurement accuracy is improved, but the temperature gradient cannot be arbitrarily set
Solution Approach 1:
The patent makes the temperature gradient adjustable by introducing a control signal that dynamically modifies the relationship between the temperature sense signal and the output signal. The operational amplifier's feedback network is configured to allow the temperature gradient to be controlled by an external signal, enabling the same circuit to adapt to different temperature measurement scales and ranges without sacrificing measurement accuracy. This dynamic control is achieved through the interaction between the temperature sense signal and the amplifier's feedback path.
Solution Approach 2:
The patent changes the electrical parameters of the circuit, specifically the resistance ratios in the feedback network, to achieve different temperature gradients. By adjusting the resistance values in the operational amplifier's feedback path, the circuit can be configured to produce different voltage outputs for the same temperature input, thereby achieving arbitrary temperature gradient settings while maintaining accurate temperature measurement through the bipolar transistor sensing mechanism.
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 enables the generation of a temperature sense signal with adjustable sensitivity and reduced offset voltage impact, enhancing the usability and accuracy of temperature sensing in CMOS integrated circuits without the need for trimming circuits.
Implementation Method 1
As an example of a temperature detector or sensor circuit using a temperature coefficient of a forward voltage of a pn junction based on a bandgap
Implementation Method 2
a temperature gradient of the temperature sense signal is uniquely determined by a resistance ratio between resistive elements set so as to cancel the temperature dependence
Data Source
AI summary
A difference between both emitter voltages of a first transistor having an emitter through which a first current flows, and at least one second transistor having an emitter through which such a second current as to reach a current density thereof smaller than that of the emitter of the first transistor flows, is applied across a first resistor. A second resistor is provided between the emitter of the second transistor and a circuit's ground potential. A third resistor and a fourth resistor are respectively provided between collectors of the first and second transistors and a power supply voltage. Such an output voltage that a collector voltage of the first transistor and a collector voltage of the second transistor become equal is formed in response to the collector voltage of the first transistor and the collector voltage of the second transistor and supplied to bases of the first and second transistors in common. A temperature sense voltage is formed from a connecting point of the first and second resistors.