DC Offset Calibration in Direct-Conversion Receivers
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Solution Overview
Problem
Direct conversion receivers face challenges in minimizing DC offsets due to varying gain settings in RF and baseband amplification stages, leading to signal saturation and reduced dynamic range, with existing calibration techniques being either slow or requiring increased semiconductor die size and cost.
Innovation Solution
The implementation of two look-up tables to store DC offset values associated with different gain settings of amplification stages, with a search logic to estimate and update these values efficiently, and a feedback loop to minimize differences between estimates, allowing for rapid adjustment of correction factors and reducing the need for exhaustive calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC offset estimation is performed for all possible gain partitioning between G2 and G3 and stored in a look-up table, then DC offset cancellation accuracy is improved, but the time required for calibration and the semiconductor die size increase significantly
Solution Approach 1:
The patent segments the DC offset estimation process by separating the estimation of DC offsets for the first amplification stage (G2) and second amplification stage (G3) into independent operations. Instead of estimating all possible combinations simultaneously, the system performs estimation for each stage independently and stores results in separate look-up tables, reducing the computational burden and calibration time while maintaining accuracy.
Solution Approach 2:
The patent applies preliminary action by performing DC offset estimation during a calibration phase before normal operation. The search logic estimates DC offsets for various gain settings and stores them in look-up tables during this preliminary calibration period. During actual operation, the system simply retrieves pre-computed values from these tables, eliminating the need for real-time exhaustive estimation and significantly reducing calibration time requirements.
2Measurement precision
If DC offset estimation is performed for all possible gain partitioning and stored in a look-up table, then DC offset cancellation accuracy is improved, but the semiconductor die size increases
Solution Approach 1:
The patent divides the large look-up table into two smaller, separate tables: one for storing DC offset values associated with different gains of the first amplification stage (G2), and another for the second amplification stage (G3). This segmentation reduces the memory requirement for each individual table while maintaining the comprehensive coverage of all gain combinations through the combined information from both tables.
Solution Approach 2:
By performing DC offset estimation during a preliminary calibration phase and storing results in look-up tables, the system eliminates the need for large real-time computation structures during operation. The calibration phase pre-computes and stores only the necessary DC offset values, reducing the semiconductor die size required for storage while maintaining accurate DC offset cancellation across all gain settings.
3Reliability
If the correction factor is rapidly adjusted as gain settings change, then signal integrity is maintained, but the complexity of the calibration system increases
Solution Approach 1:
The patent applies preliminary action by pre-computing and storing correction factors in look-up tables during a calibration phase. The search logic estimates DC offsets for various gain settings and stores the corresponding correction factors in tables during this preliminary period. During normal operation, the system simply retrieves pre-computed correction factors from these tables based on current gain settings, eliminating the need for complex real-time calculation systems while maintaining signal integrity.
Solution Approach 2:
The patent uses look-up tables to store pre-computed correction factor data, effectively creating a copy of the calibration information that can be rapidly accessed during operation. This copying approach allows the system to maintain signal integrity by having ready-access to appropriate correction factors without requiring complex real-time computation, thus reducing system complexity while preserving reliability.
Data Source
AI summary
A wireless communication receiver includes a multitude of look-up tables each storing a multitude of DC offset values associated with the gains of an amplification stage disposed in the wireless communication receiver. The entries for each look-up table are estimated during a stage of the calibration phase. During such a calibration stage, for each selected gain of an amplification stage, a search logic estimates a current DC offset number and compares it to a previous DC offset estimate that is fed back to the search logic. If the difference between the current and previous estimates is less than a predefined threshold value, the current estimate is treated as being associated with the DC offset of the selected gain of the amplification stage and is stored in the look-up table. This process is repeated for each selected gain of each amplification stage of interest until the look-up tables are populated.