Translinear Amplifier Offset Cancellation for PTAT Sensors
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Solution Overview
Problem
Existing transducer systems, such as temperature sensors, face challenges in maintaining linearity over a wide temperature range due to input referred amplifier offsets and process sensitivities, particularly in PTAT circuits that rely on precise resistor matching, leading to inaccuracies and unpredictability in temperature measurements.
Innovation Solution
A dual amplifier approach is employed where one amplifier generates a measurement voltage through feedback, and the second amplifier samples and integrates it in switched-capacitor mode, allowing for offset adjustment and cancellation, thereby maintaining linearity without resistors and reducing sensitivity to amplifier offsets. This method reuses amplifiers for various operations, saving area and power while ensuring accuracy across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PTAT circuits use precise resistor matching to maintain linearity, then measurement precision is improved, but device complexity and sensitivity to process variations worsen
Solution Approach 1:
The patent extracts and eliminates resistors from the PTAT circuit by using a translinear amplifier that generates the PTAT voltage through transistor current ratios and feedback. This removes the source of process sensitivity and matching requirements while maintaining the temperature-proportional output.
Solution Approach 2:
The translinear amplifier performs multiple functions: it generates the PTAT voltage, provides feedback control, and eliminates the need for separate resistor-based gain control. The switched-capacitor integrator also serves dual purposes of integration and offset cancellation, reducing overall circuit complexity.
2Measurement precision
If traditional amplifier offset cancellation methods are used, then measurement precision improves, but loss of time increases due to calibration requirements
Solution Approach 1:
The circuit performs offset cancellation automatically during normal operation by switching the integrator to sample and integrate the amplifier offset, then subtracting it from the measurement. This preliminary offset characterization happens continuously without requiring separate calibration steps.
Solution Approach 2:
The translinear amplifier system is self-calibrating through its inherent feedback mechanism. The integrator automatically captures and compensates for offset drifts without external intervention, making the system self-correcting and eliminating manual calibration requirements.
3Measurement precision
If multiple amplifiers are used for measurement and offset cancellation, then measurement precision improves, but area consumption increases
Solution Approach 1:
The same translinear amplifier is reused for both measurement and offset cancellation operations. The switched-capacitor integrator also serves dual purposes of integrating the measurement signal and storing offset values. This component reuse significantly reduces the total number of amplifiers and associated circuitry required.
Solution Approach 2:
The measurement and offset cancellation functions are merged into a single integrated circuit block. The integrator combines the measurement signal and offset correction in one operation, and the hold capacitors store both measurement and offset values simultaneously, reducing overall circuit footprint.
4Ease of manufacture
If resistor-based PTAT circuits are used, then ease of manufacture is improved, but manufacturing precision worsens due to process sensitivities
Solution Approach 1:
The patent removes resistors from the PTAT circuit entirely, replacing them with a translinear amplifier that uses transistor current ratios determined by geometric scaling. This eliminates sensitivity to resistor matching while maintaining ease of manufacture through standard CMOS fabrication processes.
Solution Approach 2:
The circuit transitions from resistor-based parameter control to transistor-based parameter control. The PTAT voltage is generated through transistor current ratios and feedback, which are less sensitive to process variations than resistor values. The switched-capacitor elements also provide parameter control through capacitor ratios, which can be more precisely controlled in fabrication.
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 a robust and accurate PTAT system that maintains linearity over a wide temperature range, reduces the need for system calibration, and is applicable to various transducers like image sensors, depth cameras, and other sensors, offering improved performance and efficiency.
Implementation Method 1
The first amplifier generates a measurement voltage though feedback in an analog circuit
Implementation Method 2
The second amplifier samples and integrates the measurement in a switched-capacitor mode, and the output is stored on a capacitor
Data Source
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AI summary
A transducer such as a translinear proportional-to-absolute-temperature sensor uses two amplifiers, where each amplifier is used in a variety of modes. The first amplifier generates a measurement voltage though feedback in an analog circuit. The second amplifier samples and integrates the measurement in a switched-capacitor mode, and the output is stored on a capacitor. Then the first amplifier is set to measure its offset. The offset is sampled and integrated by the second amplifier, and the output is stored on a second capacitor. Then the first and second amplifiers are set to buffer the voltages stored on the capacitors. The measurement can then be offset-adjusted by digital or analog means. The adjusted measurement is then available to be used for calibration of, e.g., an image sensor. Other transducers, such as pressure sensors, strain sensors, gyroscopes, magnetometers, accelerometers, and xyz positioning sensors may employ the same dual amplifier approach.