TMOS Amplification Interface for Temperature-Compensated Differential Sensing
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Solution Overview
Problem
Conventional measurement systems face challenges in effectively amplifying and processing signals from thermally isolated MOS (TMOS) sensors, particularly in sub-threshold conditions, due to temperature variations and common-mode disturbances, which affect the accuracy and reliability of temperature and other environmental measurements.
Innovation Solution
An amplification interface is designed with PTAT bias-current generators, a differential current integrator, and an RC oscillator to compensate for temperature variations and reject common-mode signals, using a control circuit to regulate the common mode voltage and integrate differential currents, thereby enhancing signal amplification and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional amplifier circuits are used to amplify signals from TMOS sensors, then signal amplification is achieved, but temperature variations and common-mode disturbances degrade measurement accuracy
Solution Approach 1:
The measurement system is segmented into two separate measurement paths: one for the sensing TMOS transistor and another for the reference TMOS transistor. This segmentation allows independent measurement of the sensing element and reference element, enabling differential processing to reject common-mode temperature variations while maintaining accurate measurement of the target quantity.
Solution Approach 2:
A reference TMOS transistor is introduced as an intermediary element that experiences the same temperature variations as the sensing transistor but is shielded from the target quantity (e.g., infrared radiation). The reference transistor acts as a mediator that captures common-mode disturbances, allowing these to be subtracted out in differential processing to isolate the true measurement signal.
2Measurement precision
If the TMOS transistor is thermally isolated to detect temperature variations, then temperature sensitivity is improved, but the device becomes more susceptible to common-mode temperature disturbances
Solution Approach 1:
The system uses two thermally isolated TMOS transistors segmented into separate functional roles: one sensing transistor exposed to both temperature variations and the target quantity, and one reference transistor exposed only to temperature variations. This segmentation preserves the temperature sensitivity of each transistor while enabling cancellation of common-mode temperature disturbances through differential measurement.
Solution Approach 2:
The reference TMOS transistor serves as an intermediary that captures purely the common-mode temperature disturbances. By comparing the sensing transistor output with the reference transistor output, the system isolates the target quantity signal from temperature-induced common-mode disturbances, maintaining high temperature sensitivity while rejecting unwanted temperature variations.
3Measurement precision
If PTAT bias-current generators and differential current integrators are added to the amplification interface, then temperature compensation and common-mode rejection are improved, but device complexity increases
Solution Approach 1:
PTAT (Proportional To Absolute Temperature) bias-current generators are used to dynamically adjust bias currents based on temperature. By changing the bias current parameter in proportion to absolute temperature, the system compensates for temperature-induced variations in transistor characteristics, maintaining measurement accuracy across temperature ranges without requiring complex external temperature compensation circuits.
Solution Approach 2:
The differential current integrator merges the outputs of two transconductance amplifiers into a single integrated output signal. This combining operation naturally performs differential processing, rejecting common-mode signals while amplifying differential signals. The integration function also provides signal conditioning and filtering, reducing the need for additional separate filtering stages and simplifying the overall signal processing chain.
Data Source
AI summary
A thermally-isolated-metal-oxide-semiconducting (TMOS) sensor has inputs coupled to first and second nodes to receive first and second bias currents, and an output coupled to a third node. A tail has a first conduction terminal coupled to the third node and a second conduction terminal coupled to a reference voltage. A control circuit applies a control signal to a control terminal of the tail transistor based upon voltages at the first and second nodes so that a common mode voltage at the first and second nodes is equal to a reference common mode voltage. A differential current integrator has a first input terminal coupled to the second node and a second input terminal coupled to the first node, and provides an output voltage indicative of an integral of a difference between a first output current at the first input terminal and a second output current at the second input terminal.