Amplifier Bias Feedback Loop for Low-Gain Distortion Control
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Solution Overview
Problem
Amplifiers with low gain feedback control loops experience distortions due to inability to maintain desired bias currents, leading to suboptimal performance and increased harmonic distortion in output signals.
Innovation Solution
Incorporating a positive feedback loop in parallel with the negative feedback loop to sense and compensate for the finite gain of the negative feedback loop, thereby maintaining desired bias currents and reducing distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a negative feedback control loop is used for biasing active components, then the bias voltages/currents can be maintained at desired levels, but the loop gain may be low causing distortions in the output signal
Solution Approach 1:
The patent introduces a positive feedback path in parallel with the negative feedback control loop. The positive feedback senses the finite gain of the negative feedback loop and provides compensating signals to maintain bias currents at desired levels, thereby eliminating output signal distortions caused by low loop gain while preserving the stability provided by the negative feedback
Solution Approach 2:
The positive feedback loop acts as a counterweight to compensate for the insufficient gain of the negative feedback loop. By providing an opposing feedback signal that counteracts the finite gain limitation, the system maintains accurate bias current levels without the distortions that would otherwise result from low loop gain
2Measurement precision
If the gain of the feedback control loop is increased to reduce distortions, then the bias currents can be maintained more accurately, but the stability of the system may be compromised
Solution Approach 1:
The patent segments the feedback function into two separate parallel paths: a negative feedback loop that provides system stability and a positive feedback loop that enhances bias current accuracy. This segmentation allows each feedback path to perform its specific function optimally without compromising the other, achieving high measurement precision while maintaining system stability
Solution Approach 2:
The positive feedback loop acts as an intermediary that senses the finite gain of the negative feedback loop and provides compensating signals. This intermediary mechanism allows the system to achieve accurate bias current maintenance without directly increasing the gain of the stable negative feedback loop, thereby preserving system stability while improving measurement precision
Data Source
AI summary
According to an aspect of the present invention, a stage of an amplifier contains a positive feedback loop in addition to a negative feedback loop to maintain the bias currents at a desired level in the active components providing the output of the amplifier. The positive feedback loop senses the finite gain (i.e., less than the ideal infinite gain) of the negative feedback loop and compensates for the finite gain. Due to the use of the positive feedback, the duration and extent of deviation of the bias currents from the desired level is reduced, thereby minimizing the distortions in the output of the amplifier. In an embodiment, the stage corresponds to a class AB stage.