Active RC Filter Resistor Ladder Layout for Tunable Radar Equalization
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Solution Overview
Problem
Active RC-type filters in FMCW radar devices face challenges in efficiently equalizing uneven spectral distributions of received signals, requiring tunable high-pass/low-pass filter stages that consume significant silicon area due to the need for many discrete variable components, and struggle with linearity issues from switch loading.
Innovation Solution
The implementation of an active RC-type filter with integrated capacitor and resistor banks, using series-connected resistor ladders and T-switches to reduce silicon area and minimize non-linear distortion, along with a calibration controller to optimize component values for precise filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If discrete variable components are used to create tunable filter stages, then filtering flexibility is improved, but silicon area consumption increases significantly
Solution Approach 1:
The patent combines multiple discrete variable resistor and capacitor components into integrated resistor banks and capacitor banks with shared common nodes. This merging reduces the total component count and silicon area while maintaining the ability to independently control multiple filter stages through shared control signals.
Solution Approach 2:
The resistor banks and capacitor banks are designed to serve multiple filter stages simultaneously. The same resistor bank can be shared across different filter stages, and the banks can be reconfigured through control switches to provide different resistance values for different filtering requirements, achieving multi-functionality with reduced hardware.
2Ease of manufacture
If conventional switches are used in resistor banks, then component selection is simplified, but linearity deteriorates due to switch loading effects
Solution Approach 1:
The patent introduces buffer amplifiers as intermediary elements between the control switches and the resistor banks. These buffers act as mediators that isolate the switches from the heavy loading effects of the resistor banks, allowing the switches to control high-value resistors without significant loading errors while maintaining good linearity in the overall system.
3Adaptability or versatility
If many discrete components are used for tunable filtering, then filter control range is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple discrete resistor and capacitor components into integrated banks with shared common nodes. Instead of having separate components for each filter stage, the banks are constructed with multiple resistors/capacitors connected to shared nodes, reducing the total component count while maintaining the ability to achieve wide control ranges through selective switching.
Solution Approach 2:
The resistor and capacitor banks are segmented into multiple sub-units that can be independently switched. This segmentation allows the system to achieve a wide control range by selectively connecting different segments, providing fine-grained control over the filter characteristics without requiring a proportional increase in total component count.
Data Source
Figure 1A~1B
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AI summary
In accordance with a first aspect of the present disclosure, an active RC-type filter is provided, comprising: an input, an output and a signal path between said input and output; at least one capacitor bank and at least one resistor bank, wherein said capacitor bank and resistor bank are integrated into the signal path; wherein the resistor bank comprises a plurality of resistor ladders; wherein each one of said resistor ladders comprises a plurality of resistors connected in series; wherein each one of said resistors has an input node configured to be coupled selectively to the signal path through one of a plurality of controllable switches; and wherein said resistor ladders have output nodes directly coupled to each other and to the signal path. In accordance with a second aspect of the present disclosure, a corresponding method of implementing an active RC-type filter is conceived.