Microphone Bias Filter With Adaptive Bandwidth for Fast Settling
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Solution Overview
Problem
Current MEMS transducer bias circuits with narrow filter bandwidths are inadequate for next-generation transducers requiring larger bandwidths for transient operations such as start-up and shock recovery, as they provide insufficient noise attenuation and interference suppression.
Innovation Solution
A bias circuit with a filter circuit coupled to a transducer, comprising cascaded charge pump stages and a filter circuit with voltage-controlled resistors and capacitors, adaptively configuring bandwidth for transient and steady-state operations by varying the voltage reference, enabling a larger bandwidth during transient operations and a smaller bandwidth during steady-state operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a narrow filter bandwidth is used in the bias circuit, then noise attenuation is improved, but transient operation performance deteriorates
Solution Approach 1:
The filter bandwidth is made dynamically adjustable through a voltage-controlled resistor (VCR) whose resistance is modulated by a control signal. During transient operations (start-up, shock recovery), the VCR decreases resistance to increase bandwidth for faster settling. During steady-state operation, the VCR increases resistance to narrow bandwidth for improved noise attenuation. This dynamic adaptation resolves the contradiction between fixed noise filtering and transient response requirements.
Solution Approach 2:
The patent changes the resistance parameter of the filter circuit by introducing a voltage-controlled resistor whose resistance value varies based on operational mode. The control signal adjusts the VCR resistance to switch between high-resistance state (narrow bandwidth, good noise filtering) and low-resistance state (wide bandwidth, fast transient response). This parameter modulation enables the system to optimize both noise attenuation and transient performance at different times.
2Loss of time
If a wide filter bandwidth is used to improve transient response, then settling time is reduced, but noise attenuation deteriorates
Solution Approach 1:
The filter bandwidth is dynamically controlled through the voltage-controlled resistor that responds to control signals indicating operational mode. During transient events, the control signal drives the VCR to low resistance, widening bandwidth and reducing settling time. During normal operation, the control signal drives the VCR to high resistance, narrowing bandwidth for superior noise attenuation. This time-varying control resolves the trade-off between settling speed and noise filtering.
Solution Approach 2:
The system employs periodic or event-driven control signals that switch the VCR resistance based on detected operational conditions (start-up, shock recovery, steady-state). This periodic modulation of the resistance parameter allows the filter to alternate between wide-bandwidth mode for fast settling and narrow-bandwidth mode for noise rejection, optimizing both parameters across different time intervals.
Data Source
AI summary
The disclosure relates to a transducer assembly like a microphone including a bias circuit having a charge pump and a filter circuit coupled to a transducer. The filter circuit includes a voltage-controlled resistor located between an output of the charge pump and the transducer, and a capacitor coupled to the voltage-controlled resistor opposite the charge pump, wherein the bias circuit is configured with a larger bandwidth for faster settling during transient operation than during steady-state operation.