Receiver Gain Adjustment for ADC DC Offset Handling
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Solution Overview
Problem
Direct current (DC) offset in radio frequency receivers leads to performance degradation due to signal clipping and saturation, and existing DC notch filtering methods introduce significant distortions and inter-symbol interference.
Innovation Solution
Optimizing the dynamic range of the analog-to-digital converter by determining and accounting for the DC offset value in the gain control, allowing for reduced distortion power from signal clipping and quantization, and adjusting the gain control value based on the DC offset and dynamic range characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If DC notch filtering is used to remove DC offset, then DC offset is significantly attenuated or almost completely removed, but significant distortions are introduced to the frequency characteristics near to DC
Solution Approach 1:
The patent changes the parameter being controlled from frequency-domain filtering to time-domain gain adjustment. By adjusting the gain control value based on DC offset magnitude and dynamic range characteristics, the system removes DC offset without introducing frequency distortions that occur with notch filtering.
Solution Approach 2:
The patent replaces the mechanical/filter-based DC notch filtering approach with a computational gain adjustment method. Instead of using a physical filter that distorts frequencies near DC, the system uses digital processing to adjust gain based on measured DC offset, avoiding the frequency distortion problem entirely.
2Manufacturing precision
If a narrow lowpass filter characteristic is used in DC notch filter, then distortion near DC is minimized, but the filter becomes difficult to realize and introduces long impulse response causing inter-symbol interference
Solution Approach 1:
The patent replaces the complex narrow lowpass filter implementation with a simple gain adjustment algorithm. The gain control value is determined as a function of DC offset magnitude and dynamic range characteristics, avoiding the need for complex filter structures and their associated implementation difficulties.
Solution Approach 2:
The patent changes from filtering in the frequency domain to gain control in the time domain. This parameter change eliminates the need for narrow lowpass filter characteristics and their resulting long impulse responses, thereby avoiding inter-symbol interference while maintaining simplicity.
3Object-affected harmful factors
If DC notch filter is used, then DC offset is removed, but group delay variations around the DC subcarrier are introduced causing larger channel estimation losses
Solution Approach 1:
The patent substitutes the filter-based DC removal method with a gain adjustment method that does not introduce group delay variations. By controlling gain based on DC offset magnitude and dynamic range, the system removes DC offset while preserving the phase and timing characteristics needed for accurate channel estimation.
4Manufacturing precision
If gain control is adjusted to optimize dynamic range, then trade-off between signal clipping and quantization distortion is achieved, but DC offset causes saturation or clipping effects that degrade receiver functioning
Solution Approach 1:
The patent introduces feedback by determining the gain control value as a function of the DC offset magnitude. The system measures or estimates the DC offset and uses this information to adjust the gain control, creating a closed-loop system that prevents saturation while optimizing dynamic range for the actual signal conditions.
Solution Approach 2:
The patent changes the gain control parameter dynamically based on DC offset magnitude and dynamic range characteristics. This parameter adjustment allows the system to optimize the trade-off between clipping and quantization distortion while accounting for the presence of DC offset, preventing saturation effects.
Data Source
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AI summary
The invention refers to generating a digital signal from an analog signal, wherein the analog signal is amplified according to a gain control value before being converted to a digital value by means of an analog-to-digital converter, wherein a DC offset value of the analog signal is determined, and the gain control value is generated as a function of the dynamic range of the analog-to- digital converter and the DC offset value. The invention further refers to a corresponding circuit and a computer program.