Discrete-Time Analog Filter Circuit With Rotating Capacitor Pairing
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Solution Overview
Problem
Direct sampling circuits face challenges in achieving broadband and steep filter characteristics due to limited coefficient ranges, leading to difficulties in achieving Butterworth or Chebyshev characteristics, and are hindered by aliasing issues in decimation filters.
Innovation Solution
A discrete-time analog circuit with a rotating capacitor circuit and a coefficient circuit that allows for sequential pairing changes of charge holding sections, enabling flexible setting of filter poles and zeros, and includes an antenna, low noise amplifier, and analog-to-digital conversion for enhanced signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a second-order IIR filter is used to determine the passband characteristic, then the circuit configuration is simple, but it is difficult to achieve a broadband and steep filter characteristic
Solution Approach 1:
The filter is segmented into multiple independent coefficient circuits (first coefficient circuit with capacitor C1, second coefficient circuit with capacitor C2, etc.), each capable of independently setting filter coefficients. This segmentation allows complex filter characteristics to be achieved through combination of simpler units, resolving the contradiction between circuit simplicity and filter performance.
Solution Approach 2:
The patent introduces dynamic switching mechanisms where capacitors can be selectively connected or disconnected based on control signals. This dynamic reconfiguration allows the filter characteristics to be changed in real-time, enabling broadband and steep characteristics while maintaining a relatively simple base circuit structure.
2Manufacturing precision
If the transfer function has complex poles to achieve a flat passband, then the passband characteristic is improved, but each filter coefficient can only have a value smaller than one, narrowing the range of achievable poles
Solution Approach 1:
The patent changes the parameter range of filter coefficients by introducing capacitor ratios rather than being limited to values less than one. By using the ratio of capacitor values (C1/C2, etc.), the system can achieve a much broader range of pole positions while maintaining stable passband characteristics, thus resolving the contradiction between passband quality and coefficient flexibility.
3Manufacturing precision
If decimation is performed to achieve a broadband filter characteristic, then the bandwidth is improved, but aliasing occurs at the frequency corresponding to the decimation ratio
Solution Approach 1:
The patent applies preliminary filtering action before decimation by configuring the coefficient circuits to pre-shape the spectrum. This preliminary action reduces the energy at frequencies that would cause aliasing, allowing broadband filtering to be achieved while minimizing aliasing artifacts that would otherwise occur during decimation.
Data Source
AI summary
The discrete time analog circuit (100) is provided with: a rotate capacitor circuit (150); an amplifier (141) that is connected to the input line or the output line of the rotate capacitor (150), and amplifies the input potential or input charge; a coefficient circuit (140) that is positioned in series with the amplifier (141), and has two history capacitors (143-1, 143-2) positioned parallel to each other; a first active capacitor among the two history capacitors (143-1, 143-2) that is connected to and charges the amplifier (141); and a clock generation circuit (110) that is connected to the input line or the output line without the involvement of the amplifier (141), and that sequentially changes the pairing of the rotate capacitor circuit (150) a second active capacitor, which shares a charge with the rotate capacitor circuit (150).