Programmable Analog Filter Using Quantized Capacitor Scaling
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Solution Overview
Problem
In mixed-signal circuits, achieving precise bandwidth control in programmable active filters is challenging due to variations in component values caused by processing and temperature changes, requiring a large number of capacitors and control bits, which increases layout area and cost.
Innovation Solution
A programmable active frequency-selective circuit using a combination of fixed and switchable capacitors, with a control circuit that adjusts the gain and process variations, allowing for bandwidth selection between 6 MHz and 8 MHz modes and gain selection between 0 dB and −3 dB, using a small number of capacitors and control bits, and incorporating a memory for storing parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of capacitors and control bits are used to achieve precise bandwidth control, then bandwidth precision is improved, but layout area and cost increase
Solution Approach 1:
The capacitor array is segmented into multiple groups, each group corresponding to a specific bandwidth mode (6 MHz or 8 MHz). Within each group, capacitors are switched to achieve fine-tuned bandwidth control. This segmentation allows precise bandwidth control within each mode without requiring a single large array covering the entire range, thereby reducing the total number of capacitors needed.
Solution Approach 2:
The filter circuit implements dynamic bandwidth control through switchable capacitor arrays that can be reconfigured in real-time. The control circuit dynamically selects and switches between different capacitor combinations based on the desired bandwidth mode, enabling precise and adaptive bandwidth control without requiring static, oversized capacitor arrays for all possible bandwidth values.
2Measurement precision
If a large number of capacitors and control bits are used to achieve precise bandwidth control, then bandwidth precision is improved, but device complexity increases
Solution Approach 1:
The control logic is segmented into distinct control paths for different bandwidth modes (6 MHz and 8 MHz). Each mode has its own dedicated control circuitry that manages a specific subset of capacitors. This segmentation simplifies the overall control logic compared to a single complex control unit managing all capacitors, as each mode's control can be independently optimized and implemented with simpler logic.
Solution Approach 2:
The device employs dynamic switching mechanisms that automatically transition between different capacitor configurations based on the selected bandwidth mode. This dynamic approach reduces complexity by using control bits and switches that can be programmed or configured, rather than requiring hardwired complex logic for every possible bandwidth setting. The dynamic reconfiguration capability allows the same hardware to serve multiple bandwidth precision requirements.
3Reliability
If high-precision external resistors and capacitors are used to compensate for process and temperature variations, then filter parameter stability is improved, but manufacturing cost and device complexity increase
Solution Approach 1:
The filter circuit compensates for process and temperature variations by dynamically changing the RC product parameters through switchable capacitor arrays. Instead of relying on high-precision external components with fixed values, the invention uses switchable internal capacitors that can be reconfigured to adjust the time constant, thereby compensating for environmental variations. This approach maintains filter parameter stability while using standard, cost-effective integrated components rather than expensive external precision components.
Data Source
AI summary
A programmable active frequency-selective circuit includes a first capacitor having a fixed value and a second capacitor coupled in parallel to the first capacitor and having a plurality of switchable capacitors connected in parallel to each other. The programmable active frequency-selective circuit further includes a plurality of switches each being associated with one of the switchable capacitors, and a control port coupled to the switches. The capacitors may be varied to account for processing variations that occur during manufacturing of the programmable active frequency-selective circuit. The capacitors values may also be varied to change the bandwidth and/or gain of the programmable active frequency-selective circuit.