Discrete-Time Switched-Capacitor Band-Pass Filter With Controlled Phase Shift
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Solution Overview
Problem
Existing switched-capacitor stages in MEMS gyroscopes face challenges in eliminating offset and low-frequency noise, such as flicker noise, without introducing phase shifts in the signal, which is crucial for precise control loop operations.
Innovation Solution
A switched-capacitor band-pass filter utilizing the correlated-double-sampling technique with multiple phase signals to differentiate between signal of interest and undesired components, employing feedback and sampling capacitors to cancel offset and flicker noise, while maintaining a controlled phase shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If derivative filters are used to eliminate offset in continuous-time read chain, then offset elimination is achieved, but phase shift cannot be maintained constant due to frequency drifts
Solution Approach 1:
The patent replaces continuous-time derivative filters with a discrete-time switched-capacitor band-pass filter. This substitution transforms the filtering approach from continuous analog operation to discrete time-domain sampling, enabling precise control of phase shift through digital-friendly architecture while maintaining offset elimination capability through correlated double sampling technique.
Solution Approach 2:
The patent changes the operating parameters by using discrete-time sampling with specific sampling frequencies (f1 and f2) that are higher than the signal frequency. By adjusting the sampling frequencies and the timing of switching operations, the filter maintains constant phase shift at the signal frequency even when oscillation frequency drifts occur due to aging or temperature changes.
2Measurement precision
If chopping techniques are used for offset modulation and filtering, then offset elimination is achieved, but the system becomes complex and phase shift control is poor
Solution Approach 1:
The patent extracts and separates the offset elimination function into a dedicated correlated double sampling stage before the main band-pass filtering. By taking out the offset cancellation operation as a distinct preprocessing step using sampling capacitors and switching networks, the main filter can focus on frequency-selective filtering without the complexity of modulating and demodulating signals at high frequencies.
Solution Approach 2:
The patent segments the filtering process into distinct time phases using non-overlapping clock signals (PHI1, PHI2, PHI3). The correlated double sampling operates in one phase while the band-pass filter processes in another phase, dividing the complex signal processing into manageable temporal segments that can be implemented with simple switching operations rather than complex continuous processing.
3Object-affected harmful factors
If filtering is applied to eliminate noise, then noise attenuation is achieved, but phase shifts are introduced in the signal
Solution Approach 1:
The patent employs dynamic switching operations where the timing and duration of switch closure are precisely controlled to match the signal period. The switched-capacitor band-pass filter dynamically adjusts its operation to sample the signal at optimal moments, allowing noise attenuation through frequency-selective filtering while maintaining the phase relationship of the desired signal through synchronized switching with the oscillation frequency.
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
Effectively eliminates offset and flicker noise up to higher frequencies than the signal of interest, maintaining a controlled phase shift, even with variations in oscillation frequency due to aging or temperature changes, ensuring precise signal processing in MEMS gyroscope control loops.
Implementation Method 1
A switched-capacitor band-pass filter utilizing the correlated-double-sampling technique with multiple phase signals to differentiate between signal of interest and undesired components
Implementation Method 2
employing feedback and sampling capacitors to cancel offset and flicker noise
Data Source
AI summary
A band-pass filter made up by an operational amplifier and by an input circuit. The input circuit is formed by a capacitive filtering element, connected to the input of the operational amplifier; a coupling switch, coupled between an input node and the capacitive filtering element; a capacitive sampling element, coupled between the input of the filter and the input node; and a sampling switch, coupled between the input node and a reference-potential line. The coupling switch and the input sampling switch close in phase opposition according to a succession of undesired components sampling and sensing steps, so that the capacitive sampling element forms a sampler for sampling the undesired component in the undesired components sampling step, in the absence of the component of interest, and forms a subtractor of the undesired components from the input signal in the sensing step.