Rotating Coefficient FIR Filter Without Delay Elements
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Solution Overview
Problem
Existing FIR filters require delay elements and adjustable impedances, which complicate signal delay and introduce noise due to digital busses, and often necessitate a large number of switches, making them complex and prone to noise degradation.
Innovation Solution
A rotating coefficient FIR filter design that uses pre-selected sets of impedance elements and a minimum number of switches, where all necessary coefficient sets are present simultaneously, eliminating the need for delay elements and adjustable impedances, and reducing switch count to minimize noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If delay elements and adjustable impedances are used to implement FIR filters, then the desired frequency response can be achieved, but the device complexity increases and noise is introduced
Solution Approach 1:
The patent pre-calculates and stores multiple coefficient sets in lookup tables before operation. During filter operation, the pre-computed coefficient sets are directly retrieved and applied without real-time calculation or adjustment, eliminating the need for adjustable impedances and reducing device complexity while maintaining frequency response accuracy
Solution Approach 2:
The patent replaces the mechanical/physical delay elements and adjustable impedance components with digital lookup tables and switching circuitry. The coefficient selection is achieved through digital switching between pre-stored sets rather than through physical adjustment mechanisms, reducing noise and complexity
2Adaptability or versatility
If adjustable impedances are used to provide coefficient values, then the filter can be configured for different frequency responses, but noise is introduced due to digital busses and switching
Solution Approach 1:
All possible coefficient sets corresponding to different frequency responses are pre-calculated and stored in lookup tables before operation. The system only performs simple table lookup and switching during operation, minimizing the number of switches required and reducing switching noise compared to adjustable impedance approaches
Solution Approach 2:
The patent creates multiple copies of coefficient sets stored in separate lookup tables, each representing a different frequency response configuration. The desired configuration is achieved by selecting and activating the appropriate pre-stored copy rather than adjusting a single set of impedances, reducing switching activity and noise
3Adaptability or versatility
If a large number of switches are used to implement the filter, then all coefficient sets can be present simultaneously, but the device becomes more complex and prone to noise degradation
Solution Approach 1:
The patent segments the coefficient storage into multiple separate lookup tables, with each table containing a specific coefficient set. This segmentation allows independent management and selection of coefficient sets, reducing the complexity of the switching network compared to a single large switch matrix
Solution Approach 2:
The patent pre-organizes all coefficient sets in lookup tables before operation. During filter operation, only simple selection switching is required to activate the appropriate pre-arranged coefficient set, rather than requiring complex real-time switching to assemble coefficients dynamically
Data Source
AI summary
A circuit that provides a rotating coefficient FIR filter with all necessary coefficient sets present at the same time, without the need for delay elements or devices providing for adjustable impedances is described. An input signal is sampled in round robin fashion by a plurality of sample and hold devices. The outputs of the sample and hold devices are connected to sets of impedance devices. Each set of impedance devices implements the coefficients of the desired frequency response of the filter. The impedance devices in each set are connected to the sample and hold devices in a different order from each other set, so that each set of impedance devices will produce the desired frequency response when a different one of the sampling circuits contains a new sample of the input signal. Switches connect the sets of impedance devices to an output, only one switch being closed at a time to provide the output signal.