Capacitive Sensor Amplifier With Bias-Sensed Servo Bandwidth
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing amplifier circuits for capacitive sensors, such as MEMS microphones, face challenges in quickly settling to their final DC bias voltage level during startup, leading to noise and phase delays due to fixed bandwidth settings that do not adequately compensate for the rate of change of the bias voltage during the settling phase.
Innovation Solution
An adaptive feedback loop control mechanism that dynamically adjusts the bandwidth of the amplifier circuit based on the sensed rate of change of the bias voltage, allowing for minimum required bandwidth during settling and reducing noise and phase delays, while ensuring the bandwidth does not interfere with the output signal bandwidth during normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the bandwidth of the DC servo loop is increased to compensate for the rate of change of bias voltage during settling, then the startup time is reduced, but the bandwidth of the output signal is reduced resulting in increased noise level and excessive phase delay
Solution Approach 1:
The patent applies dynamics by making the bandwidth of the DC servo loop variable rather than fixed. The bandwidth is dynamically adjusted based on the operating state: during the settling phase when bias voltage is changing, the bandwidth is increased to compensate for rate of change and reduce startup time. After settling completes, the bandwidth is reduced to its normal operating level to maintain signal fidelity with minimal noise and phase delay. This dynamic adaptation resolves the contradiction between fast startup and low noise performance.
Solution Approach 2:
The patent changes the parameter of bandwidth from a constant value to a variable value that adapts to different operational phases. During settling, the bandwidth parameter is increased to handle the rapid voltage changes. After settling, the bandwidth parameter is decreased to optimize signal quality. This parameter change strategy allows the system to achieve both fast startup and low noise performance at different times, resolving the technical contradiction.
2Reliability
If the bandwidth of the DC servo loop is set low to maintain signal bandwidth, then noise and phase delay are minimized, but the ability to compensate for rate of change of bias voltage during settling is insufficient
Solution Approach 1:
The patent implements periodic action by dividing the operation into distinct phases: a settling phase where high bandwidth is used to quickly establish the bias voltage, followed by a normal operation phase where low bandwidth is used to minimize noise. The system transitions between these phases based on whether settling is complete. This periodic switching of bandwidth levels allows the system to achieve both fast settling and low noise performance at appropriate times.
3Device complexity
If a fixed bandwidth is used in the amplifier circuit, then the circuit design is simplified, but the circuit cannot adequately compensate for varying rates of change of bias voltage during settling
Solution Approach 1:
The patent uses feedback by monitoring the state of the bias voltage (whether settling is complete or not) and using this information to adjust the bandwidth of the DC servo loop. The feedback mechanism detects when the bias voltage has settled and triggers the bandwidth reduction. This feedback-based control allows the system to automatically adapt its bandwidth without requiring complex manual configuration, resolving the contradiction between simplicity and performance.
Data Source
AI summary
An amplifier circuit (AC) for amplifying an output signal (OS) of a capacitive sensor (M) comprises a first input terminal (AIN) to receive the output signal (OS) of the capacitive sensor (M) and a second input terminal (BIN) to receive a bias voltage (Vbias) of the capacitive sensor (M). The amplifier circuit (AC) comprises an amplifier (A) for amplifying the output signal (OS) and a control circuit (CF) arranged in a feedback loop (FL) of the amplifier (A) being configured to control a DC voltage level at an input connection (A1) of the amplifier (A). A bias voltage sensing circuit (BVS) senses a change of the level of the bias voltage (Vbias) at the second input terminal (BIN) and changes the bandwidth of the feedback loop (FL) in dependence on the sensed change of the level of the bias voltage (Vbias).