Variable Gain Amplifier Recentering for ADC Dynamic Range
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Solution Overview
Problem
Variable gain amplifiers in NFC devices face issues with common mode voltage offsets, leading to signal saturation and errors in digital conversion due to increased dynamic range requirements, which are costly and energy-intensive to address by oversizing analog-to-digital converters.
Innovation Solution
A variable gain amplifier with separate amplification and recentering branches, utilizing resistive elements and digitally driven current sources to recenter signals and adapt gain in real-time, ensuring signals remain within the dynamic range of the converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gain of the amplifier is increased to amplify weak signals, then the signal amplitude increases, but the offset voltage is also amplified causing the signal to exceed the converter's dynamic range
Solution Approach 1:
The amplifier is divided into two separate branches: a first amplification branch and a second recentering branch. The first branch amplifies the differential signal while the second branch generates a compensating offset signal. This segmentation allows independent control of signal amplification and offset compensation, resolving the contradiction between amplifying weak signals and maintaining dynamic range compliance.
Solution Approach 2:
A second amplification branch acts as an intermediary to generate a compensating signal that counterbalances the offset voltage. This intermediary branch receives the same input signal and produces an inverted offset component that, when combined with the first branch output, cancels the excessive offset while preserving the amplified signal within the converter's dynamic range.
2Manufacturing precision
If oversizing the analog-to-digital converter is used to increase dynamic range, then the converter can handle offset voltages, but energy consumption and circuit area increase
Solution Approach 1:
The offset voltage component is extracted and handled separately from the main signal path. Instead of requiring the ADC to handle the full dynamic range including large offset voltages, the offset is compensated by the second amplification branch before conversion. This allows the use of a smaller, more energy-efficient converter while maintaining the ability to handle offset voltages through the dedicated recentering branch.
3Device complexity
If a single amplification branch is used, then the device complexity is low, but offset compensation is not achieved leading to signal saturation
Solution Approach 1:
The two amplification branches are merged at their outputs to combine the amplified signal from the first branch with the compensating signal from the second branch. This merging occurs through the common load impedance, where the currents from both branches combine to produce the final output signal with reduced offset, achieving offset compensation without requiring complex additional circuitry beyond the parallel branch structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively compensates for signal offsets, preventing saturation and reducing energy consumption and costs by maintaining signals within the converter's dynamic range, thereby improving the accuracy of digital signal conversion.
Implementation Method 1
a follower transistor, the gate of the follower transistor being coupled to the input terminal, the drain being coupled to the output terminal
Implementation Method 2
a resistive element of variable resistance, the resistive element being able to be driven by a variable gain controller
Implementation Method 3
a digitally driven variable current source, the variable current source being able to be driven by a compensation current driver unit
Data Source
AI summary
A variable gain amplifier includes a pair of amplification and recentering branches. Each branch includes: a resistive element of variable resistance configured to be driven by a variable gain controller; a digitally-driven variable current source configured to be driven by a compensation current driver unit; a first transistor comprising a gate terminal coupled to an input terminal of the variable gain amplifier, and a source terminal coupled to a first terminal of the resistive element; and a second transistor comprising a gate terminal coupled to a drain terminal of the first transistor, and a source terminal coupled to an output terminal of the variable gain amplifier.