Constant Bandwidth DC Offset Correction in Amplifiers
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Solution Overview
Problem
Direct conversion receivers face challenges with random DC offset voltages caused by local oscillator self-mixing and active amplifier stages, leading to saturation, and conventional feedback loops struggle to maintain constant bandwidth as the amplifier gain varies.
Innovation Solution
A system with DC offset correction feedback loops using variable gain transconductors and integration capacitors, coupled with a control circuit that adjusts transconductance in relation to amplifier gain, ensuring constant bandwidth through exponential control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional feedback loop is used to correct DC offset voltages, then DC offset correction is achieved, but the bandwidth of the feedback loop changes with the gain of the amplifier stage, preventing constant bandwidth operation
Solution Approach 1:
The patent applies dynamics by making the feedback loop bandwidth adaptive through a variable gain transconductor whose gain is controlled by a control signal. This allows the feedback loop to dynamically adjust its bandwidth in response to changes in amplifier stage gain, maintaining effective DC offset correction across varying operating conditions while preserving constant bandwidth characteristics.
Solution Approach 2:
The patent changes the transconductance parameter of the variable gain transconductor in the feedback loop based on the amplifier stage gain. By adjusting this parameter through a control signal, the feedback loop maintains constant bandwidth even as the amplifier gain varies, resolving the contradiction between DC offset correction and bandwidth constancy.
2Adaptability or versatility
If the gain of the amplifier stage is continuously varied by an analog control signal, then adaptability is improved, but the bandwidth of the feedback loop cannot remain constant, degrading DC offset correction performance
Solution Approach 1:
The patent uses feedback by continuously monitoring the output of the amplifier stage and feeding back a correction signal through the variable gain transconductor. This feedback mechanism automatically adjusts to maintain DC offset correction performance even when the amplifier gain is varied by an analog control signal, resolving the contradiction between gain adaptability and correction reliability.
Solution Approach 2:
The variable gain transconductor dynamically adjusts its transconductance in response to changes in amplifier gain, ensuring that the feedback loop maintains constant bandwidth and effective DC offset correction throughout the full range of amplifier gain variation.
3Stability of the object's composition
If the bandwidth of the feedback loop is made constant, then DC offset correction stability is improved, but the amplifier gain must remain fixed, reducing adaptability
Solution Approach 1:
The patent resolves this contradiction by making the feedback loop dynamically adaptive through a variable gain transconductor. The transconductor's gain is continuously adjusted based on the amplifier stage gain, allowing the feedback loop to maintain constant bandwidth characteristics while accommodating variable amplifier gain operation.
Solution Approach 2:
The transconductance parameter of the variable gain transconductor is changed in response to amplifier gain variations, ensuring that the feedback loop bandwidth remains constant regardless of amplifier gain settings. This parameter adjustment maintains both stability and adaptability simultaneously.
Data Source
AI summary
According to one embodiment, a system for constant bandwidth DC offset correction in an amplifier includes a number of amplifier stages having an input and an output coupled together in series. The system for constant bandwidth DC offset correction further includes a number of DC offset correction feedback loops which include a variable gain transconductor coupled to an integration capacitor further coupled to a fixed gain transconductor. Each of the DC offset correction feedback loops are coupled to the input and output of each of the number of amplifier stages. The transconductance of the variable gain transconductor in each of the number of DC correction feedback loops is varied in relation to a gain of the number of amplifier stages, such that the DC offset correction feedback loops provide DC offset correction while maintaining a constant bandwidth.