DC Offset Cancellation Circuits with Parallel Stages
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Solution Overview
Problem
Existing methods for reducing DC offset in electronic systems, particularly in wireless receivers, are inefficient due to slow and unstable feedback loops, limited accuracy, and complexity in calibration, especially when dealing with varying gain settings and rapid frequency changes.
Innovation Solution
The implementation of DC offset cancellation circuits with parallel stages and variable cutoff frequencies, including a mixer with multiple DC offset cancellation stages and a variable gain amplifier with integrated DC offset cancellation, allows for rapid and accurate DC offset reduction across different local oscillator frequencies and gain settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional feedback loops are used for DC offset cancellation, then DC offset reduction is achieved, but the system suffers from slow response time and instability
Solution Approach 1:
The DC offset cancellation is divided into two independent parallel paths: a fast path using capacitor-based AC coupling that immediately blocks DC components, and a slow path using traditional feedback loops for precise DC offset measurement and cancellation. This segmentation allows the system to achieve both fast response (through the capacitor path) and high accuracy (through the feedback path) without the instability-problem of traditional single-loop approaches.
2Measurement precision
If calibration is performed to improve DC offset cancellation accuracy, then measurement precision improves, but calibration time increases and system complexity increases
Solution Approach 1:
The system performs preliminary DC offset cancellation immediately upon signal reception using the fast capacitor-based AC coupling path, without waiting for calibration. The calibration process then refines the DC offset measurement in the background, and the corrected values are applied to further improve cancellation accuracy. This allows the system to achieve accurate DC offset cancellation without requiring extended calibration time before operation.
3Adaptability or versatility
If multiple DC offset cancellation stages are used for different frequencies, then adaptability to frequency changes improves, but device complexity increases
Solution Approach 1:
The capacitor-based AC coupling path serves as a universal DC blocking mechanism that is effective across all frequencies simultaneously, eliminating the need for separate frequency-specific cancellation circuits. The feedback loop path uses a single universal DC offset measurement and cancellation mechanism that adapts to any frequency through software control, rather than requiring hardware changes for each frequency.
4Speed
If gain settings are changed rapidly, then system responsiveness improves, but DC offset cancellation accuracy deteriorates due to calibration instability
Solution Approach 1:
The DC offset cancellation operates continuously through the capacitor-based AC coupling path regardless of gain changes, providing uninterrupted DC blocking. The feedback loop simultaneously continues to measure and update DC offset values in real-time, ensuring that accurate cancellation is maintained even during rapid gain transitions without interruption or instability.
Data Source
AI summary
Embodiments of the present invention include circuits and methods for reducing DC Offset. In one embodiment the present invention includes storing DC offset on internal capacitances. In one embodiment, parallel stages are used to remove DC offset corresponding to different local oscillator frequencies. Embodiments of the invention further include changing the low cutoff frequency of the DC cancellation circuits for fast calibration. In a first state, a high pass filter may have a first low cutoff frequency, and in a second state the high pass filter may have a second cutoff frequency lower than the first low cutoff frequency. The present invention also includes a variable gain amplifier with reduced DC offset.