Passive Charge-Sharing IIR Filter for Low-Power Analog Signals
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Solution Overview
Problem
Conventional digital time domain filters require significant resources and high clocking rates for processing analog signals, and existing analog filters often rely on active elements that increase complexity and power consumption.
Innovation Solution
A passive charge sharing approach is used to implement infinite impulse response filters, utilizing capacitors to store delayed samples of input and output signals, with configurable switching elements and charge scaling circuits to achieve efficient filtering without the need for digital signal processing hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional digital time domain filters are used to process analog signals, then filtering accuracy is improved, but resource consumption and clocking rate requirements increase significantly
Solution Approach 1:
The patent replaces digital signal processing hardware with an analog charge sharing circuit that directly processes analog signals. The digital filter computation is substituted by physical charge redistribution among capacitors, eliminating the need for digital-to-analog conversion and reducing hardware resource requirements while maintaining filtering accuracy.
Solution Approach 2:
The patent changes the operating domain from digital to analog by utilizing charge quantities as the fundamental parameter for signal processing. Filter coefficients are implemented as fixed capacitor ratios, transforming the filtering operation into a physical charge sharing process that occurs naturally through capacitor connections, thereby reducing computational complexity and resource consumption.
2Adaptability or versatility
If active elements are used in analog filters to implement filtering operations, then filtering functionality is achieved, but circuit complexity and power consumption increase
Solution Approach 1:
The patent extracts and eliminates active elements (amplifiers, operational amplifiers) from the filter circuit by implementing the filtering function purely through passive charge sharing among capacitors. The complex active circuitry is replaced with simple capacitor connections controlled by switches, dramatically reducing circuit complexity while preserving filtering functionality.
Solution Approach 2:
The patent enables the circuit to perform filtering operations autonomously through natural charge redistribution. When capacitors are connected in parallel through switches, charge automatically redistributes according to capacitor ratios, eliminating the need for active control elements and reducing both circuit complexity and power consumption.
3Adaptability or versatility
If active elements are used in analog filters, then filtering operations can be performed, but power consumption increases
Solution Approach 1:
The filtering operation is performed passively through natural charge redistribution among capacitors without requiring active power consumption. The only power consumption occurs during brief switching transitions, while the actual filtering computation occurs passively through charge sharing, dramatically reducing overall power consumption compared to active element-based filters.
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
This method enables low-power, compact signal processing with reduced resource requirements, suitable for applications like hearing aids and analog-to-digital converters, effectively preventing aliasing and eliminating DC offset in signals.
Implementation Method 1
Delayed samples of an input signal are stored as charges on capacitors of a first array of capacitors, and delayed samples of the output signal are stored as charges on capacitors of a second array of capacitors
Implementation Method 2
Outputs are determined by passively coupling capacitors of the first and second arrays to one another, and determining the output according to a total charge on the coupled capacitors
Data Source
AI summary
An approach to time domain filtering uses a passive charge sharing approach to implement an infinite impulse response filter. Delayed samples of an input signal are stored as charges on capacitors of a first array of capacitors, and delayed samples of the output signal are stored as charges on capacitors of a second array of capacitors. Outputs are determined by passively coupling capacitors of the first and second arrays to one another, and determining the output according to a total charge on the coupled capacitors. In some examples, a gain is applied to the total charge prior to storing the output on the second array of capacitors. In some examples, a charge scaling circuit is applied to the charges stored on the arrays prior to coupling capacitors to form the output.