Variable Gain Amplifier Topology for Linear Digital Gain Steps
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Solution Overview
Problem
Existing digitally controlled variable gain amplifiers face challenges in maintaining linear voltage gain behavior due to finite input and output impedances, leading to Integral Non-Linearity errors, and existing solutions like adding passive or dummy active components introduce additional losses and mismatches.
Innovation Solution
A digitally controlled variable gain amplifier design that includes a positive amplification stage and a corresponding negative amplification stage, equally weighted and coupled in parallel, allowing both stages to contribute to amplification output levels without additional losses, ensuring equal input and output impedances and achieving linear voltage gain behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dummy active components are added to equalize impedance, then input/output impedance equalization is improved, but device complexity and circuit footprint increase
Solution Approach 1:
The patent applies the anti-weight principle by introducing a negative amplification stage that produces an equal but opposite impedance effect to counterbalance the finite input/output impedances of the positive amplification stage. This allows impedance equalization without adding dummy components, as the negative stage's impedance characteristics actively cancel out the unwanted impedance effects of the positive stage.
Solution Approach 2:
The patent combines positive and negative amplification stages into a unified digitally controlled variable gain amplifier structure. This composite architecture integrates both stages with shared control logic and parallel coupling, creating a system where the combined impedance characteristics achieve equalization while maintaining a compact footprint smaller than separate stages with dummy components.
2Manufacturing precision
If passive components are added for impedance equalization, then impedance matching is improved, but energy losses increase
Solution Approach 1:
The negative amplification stage generates an opposing impedance effect that actively counterbalances the finite impedances, eliminating the need for passive equalization components. Since active amplification stages have high efficiency, this approach avoids the significant energy losses inherent in passive RC or LC equalization networks.
3Measurement precision
If multiple amplifiers are stacked for discrete gain control, then gain resolution is improved, but input/output impedance variations increase causing non-linearity
Solution Approach 1:
The patent introduces a negative amplification stage with inverted digital control that produces impedance effects equal in magnitude but opposite in sign to those of the positive stage. As digital codes switch individual amplifiers on/off in the positive stage, the negative stage simultaneously switches corresponding amplifiers to maintain constant total impedance, canceling out the impedance variations that would otherwise cause gain non-linearity.
Solution Approach 2:
The system employs digital feedback control where the same digital code that controls the positive amplification stage is inverted to control the negative amplification stage. This feedback mechanism ensures that whenever a positive amplifier is switched on, a corresponding negative amplifier is switched off, maintaining constant impedance and linear gain behavior throughout the digital control range.
4Stability of the object's composition
If dummy amplifiers are used for impedance equalization, then impedance stability is improved, but capacitive load and matching losses increase
Solution Approach 1:
Instead of using dummy amplifiers terminated in AC ground that add parasitic capacitive loads, the patent employs an active negative amplification stage that dynamically counterbalances impedance variations. This active approach maintains impedance stability without introducing the harmful capacitive effects of dummy components, as the negative stage amplifiers remain actively controlled rather than being passive terminations.
Data Source
AI summary
A digitally controlled variable gain amplifier (VGA) for generating amplification output levels is disclosed. In one aspect, the digitally controlled VGA includes a positive amplification stage including at least two positive amplifiers, and a corresponding negative amplification stage coupled to the positive amplification stage. The negative amplification stage includes at least two negative amplifiers. The positive amplification stage and the corresponding negative amplification stage are digitally controlled by one or more digital codes. The corresponding negative amplification stage is coupled in parallel with the positive amplification stage and is equally weighted as the positive amplification stage, and both the positive amplification stage and the corresponding negative amplification stage selectively contribute to the generation of the amplification output levels for the digitally controlled VGA.