Continuous-Time Complex Filter Calibration Using Dual-Tone Feedback
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Solution Overview
Problem
Current methods for tuning continuous-time complex filters in integrated circuits are inaccurate due to fabrication tolerances, leading to deviations in filter response and attenuation of desired signals, with existing techniques failing to perfectly restore the intended filter performance.
Innovation Solution
The proposed solution involves a digital auto-tuning scheme using a binary search algorithm and a digital calibration module with DACs and ADCs to directly tune the filter, applying test tones and narrow-band signals to adjust the filter's capacitance and achieve accurate calibration, specifically for second-order Gm-C bandpass filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional tuning methods are used for continuous-time complex filters, then the filter can be adjusted after fabrication, but the tuning accuracy is insufficient due to fabrication tolerances
Solution Approach 1:
The patent employs feedback mechanisms where the filter response is measured and used to adjust tuning parameters iteratively. The system measures the actual filter characteristics, compares them with desired specifications, and applies corrective tuning adjustments based on the measured deviations, thereby achieving high tuning accuracy despite fabrication variations.
Solution Approach 2:
The patent changes physical parameters of the filter circuit during tuning, specifically adjusting capacitance values through variable capacitors and modifying resistor values through programmable resistor arrays. These parameter changes allow the filter characteristics to be precisely adjusted after fabrication to compensate for manufacturing tolerances.
2Reliability
If existing tuning techniques are applied, then some filter characteristics can be restored, but the intended filter performance is not perfectly achieved
Solution Approach 1:
The system uses feedback loops that continuously monitor filter response characteristics and adjust tuning parameters to minimize deviations from desired performance. This iterative feedback process ensures that both magnitude and phase responses are accurately restored to their intended specifications.
Solution Approach 2:
The patent applies excessive tuning adjustments initially and then refines them through iterative measurement and correction. By overshooting the target parameters and then back-adjusting based on measured responses, the system achieves more precise filter performance restoration than would be possible with single-step tuning.
3Device complexity
If direct tuning methods are used, then the filter can be adjusted without replica circuits, but the tuning accuracy for complex filters remains insufficient
Solution Approach 1:
The patent extracts the tuning control functions directly from the filter circuit itself, eliminating the need for separate replica circuits. The tuning mechanisms are integrated within the filter structure, allowing direct adjustment of filter parameters without requiring external reference circuits, thereby simplifying the overall system while maintaining tuning accuracy.
Solution Approach 2:
The patent replaces mechanical or analog replica-based tuning systems with digital control mechanisms. Digital-to-analog converters and programmable logic control the tuning parameters, substituting complex analog replica circuits with programmable digital systems that achieve comparable or superior tuning accuracy with reduced hardware complexity.
Data Source
AI summary
A first and second input tone are applied to a continuous-time complex filter within an integrated circuit. The magnitude of the output of the filter at the frequency of each of the first and second input tones are measured and compared to determine the value of a filter tuning control signal. A tuning control signal is applied to the filter with the determined value to tune the filter.