Time-Varying RC Filters for Sharp Programmable Selectivity
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Solution Overview
Problem
Current analog filter designs, particularly in reconfigurable receivers, face challenges such as high power consumption, increased chip area, and limited selectivity, especially at radio-frequency stages, due to the use of traditional continuous-time or discrete-time active filters and passive filters with weak selectivity.
Innovation Solution
The development of a programmable analog filter that periodically modulates its behavior using variable components, specifically by varying the resistance in passive switched-resistor networks, to achieve sharp selectivity and high programmability, suitable for low-power applications in communications receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional continuous-time or discrete-time active filters are used at baseband, then filtering functionality is provided, but sharp selectivity is difficult to achieve and integration cost increases
Solution Approach 1:
The patent applies dynamics by making the filter components time-varying rather than static. Specifically, it uses periodically time-varying resistors and capacitors that change their values at different time intervals to achieve sharp selectivity. This dynamic approach allows a simple passive RC circuit to provide filtering performance comparable to complex active filters, resolving the contradiction between selectivity and integration cost.
Solution Approach 2:
The patent employs periodic action through time-division multiplexed switching of filter components. The resistors and capacitors are switched periodically at different rates to create effective filtering at multiple frequency bands. This periodic modulation enables a single passive circuit to replace multiple active filter stages, achieving sharp selectivity without increasing integration complexity.
2Adaptability or versatility
If passive filters with impedance translation are used at RF, then bandpass frequency and bandwidth programmability is achieved, but selectivity remains very weak
Solution Approach 1:
The patent resolves this contradiction by making the passive filter components dynamic and time-varying. By periodically modulating the resistor and capacitor values, the filter achieves both programmability and sharp selectivity. The time-division multiplexed switching allows the same physical components to provide different filtering characteristics at different time intervals, enabling both adaptability and precision.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the resistance and capacitance values through switching. The effective filter parameters (cutoff frequency, bandwidth, center frequency) are changed by selecting different resistor and capacitor combinations at different time intervals. This allows programmable control of filter characteristics while maintaining sharp selectivity through the periodic modulation effect.
3Adaptability or versatility
If DT filters are used to provide bandwidth re-configurability, then frequency adaptability is achieved, but chip area and power consumption increase
Solution Approach 1:
The patent extracts the active filtering functionality and replaces it with a passive time-varying RC circuit. By removing the need for active components (operational amplifiers, etc.) and using only passive resistors, capacitors, and switches, the design achieves bandwidth re-configurability with significantly reduced power consumption. The filtering action is extracted from the active domain and implemented in the passive time-division multiplexed domain.
Solution Approach 2:
The patent uses simple passive RC components that are cheap to integrate and consume minimal power. Rather than using complex active filter circuits that require continuous power supply, the invention uses simple resistor-capacitor pairs that are switched periodically. These passive components can be easily integrated and consumed minimal energy, achieving re-configurability through time-division multiplexing rather than through complex active circuitry.
4Adaptability or versatility
If integration sampling is used to achieve clock-programmable bandwidth, then frequency programmability is provided, but roll-off is slow and additional stages are required
Solution Approach 1:
The patent applies dynamics by using periodically time-varying RC components instead of static filters. The time-division multiplexed switching of resistors and capacitors creates effective sharp roll-off characteristics that are not achievable with static passive or active filters. The dynamic modulation of component values enables the filter to achieve steep transition bands while maintaining bandwidth programmability through clock control.
Solution Approach 2:
The patent uses periodic action through time-division multiplexed switching to achieve sharp roll-off. By switching the RC components at specific periodic intervals synchronized with the sampling clock, the filter creates effective notches and sharp transitions in the frequency response. This periodic modulation enables single-stage sharp filtering without requiring multiple cascaded stages, resolving the contradiction between programmability and roll-off sharpness.
Data Source
AI summary
A method and apparatus for selective programmable filtering using analog circuits with time-varying components (e.g., resistances, capacitances) is presented. An analog front end receives an electronic signal and filters said signal by a passive or active continuous-time filter, having a combination of equivalent memory-less (e.g., resistive) and memory (e.g., capacitive or inductive) elements. A variable resistor circuit allows switching through a range of values to control one or more of the equivalent resistances of the passive or active continuous-time filter. The variable resistors are controlled using a control circuit to periodically modulate the resistances in the continuous-time filter between periodic sampling instances, such as during analog to digital conversion. Such periodic modulation of the resistances in the continuous-time filter allows for the programming and enhancement of the selectivity of said filter.