Bolometer Readout Circuits for Common-Mode Interference Rejection
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Solution Overview
Problem
MEMS sensors, particularly bolometer arrays, face overwhelming interference from ambient conditions and self-heating, leading to significant noise that dominates the intended thermal image signal, reducing dynamic range and clarity.
Innovation Solution
The proposed solution involves using a reference sensor and an active sensor with current sources and a voltage driver to track common mode changes, generating a bias voltage that compensates for these interferences, thereby improving accuracy and reducing the input range requirements of subsequent ADCs without additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional readout circuits are used for bolometer arrays, then the circuit structure is simple, but common mode changes from ambient conditions and self-heating dominate the signal and reduce measurement accuracy
Solution Approach 1:
A reference sensor is introduced as an intermediary element that experiences the same common mode interference (ambient temperature changes and self-heating) as the active sensors but does not receive the thermal image signal. The reference sensor's output is used to generate a common mode rejection signal that is subtracted from the active sensor outputs, thereby eliminating the harmful common mode effects while preserving the desired thermal image information
Solution Approach 2:
The readout circuit implements feedback by continuously monitoring the reference sensor output and using it to adjust the common mode rejection signal. This feedback mechanism dynamically compensates for changing ambient conditions and self-heating effects, maintaining measurement accuracy over time and across different operating conditions
2Measurement precision
If additional circuitry is added to reduce common mode effects, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The reference sensor and active sensors are merged into a single integrated readout circuit architecture. The common mode rejection is achieved by combining the reference sensor output with the active sensor outputs through shared circuit elements, including the same transimpedance amplifiers and signal processing paths, thereby reducing overall circuit complexity while maintaining measurement precision
Solution Approach 2:
The reference sensor serves multiple functions: it provides common mode interference measurement, generates the rejection signal, and enables dynamic compensation for ambient conditions and self-heating. This multi-functionality eliminates the need for separate dedicated circuits for each compensation function, reducing overall device complexity
3Measurement precision
If additional circuitry is added to reduce common mode effects, then measurement accuracy improves, but power consumption increases
Solution Approach 1:
The reference sensor and active sensors share common circuit resources including transimpedance amplifiers, bias voltage generation, and signal processing pathways. This merging eliminates redundant circuitry that would otherwise consume additional power, achieving common mode rejection with minimal power overhead
Data Source
AI summary
Methods of sensor readout and calibration and circuits for performing the methods are disclosed. In some embodiments, the methods include driving an active sensor at a voltage. In some embodiments, the methods include use of a calibration sensor, and the circuits include the calibration sensor. In some embodiments, the methods include use of a calibration current source and circuits include the calibration current source. In some embodiments, a sensor circuit includes a Sigma-Delta ADC. In some embodiments, a column of sensors is readout using first and second readout circuits during a same row time.