Differential Amplifier Compensation for Feedback Non-Linearity
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Solution Overview
Problem
Conventional operational amplifiers suffer from velocity saturation effects that lead to significant odd harmonics due to large voltage swings across feedback resistors, requiring large-sized resistors that increase circuit size without efficient harmonic improvement.
Innovation Solution
A fully-differential amplifier architecture with a compensation circuit that provides inverse phase feedback or feed-forward paths, using compensation resistors with greater resistance than feedback resistors, designed to minimize non-linearity and reduce circuit size through inverse paralleling linearization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large-sized feedback resistor is used to sustain large voltage swing, then the third-order harmonic is improved, but the circuit size becomes very large
Solution Approach 1:
The feedback path is segmented into two parallel paths: one with the feedback resistor and another with the compensation capacitor. This segmentation allows each component to handle specific frequency ranges, with the capacitor compensating for high-frequency non-linearity while the resistor handles low-frequency signals, achieving harmonic improvement without requiring an excessively large resistor
Solution Approach 2:
The invention changes the electrical parameters by introducing a compensation capacitor with specific capacitance value connected in parallel with the feedback resistor. This parameter change creates a frequency-dependent feedback network that reduces the voltage coefficient effect at high frequencies, improving harmonic distortion without increasing the feedback resistor size
2Manufacturing precision
If the width of the feedback resistor is increased by 2N times, then the third-order harmonic is improved by N*12 dB, but the feedback resistor becomes too huge in size
Solution Approach 1:
A compensation capacitor is introduced as an intermediary element that mediates the feedback action at high frequencies. The capacitor provides an alternative current path that bypasses the resistive non-linearity, effectively reducing the voltage coefficient impact without requiring the feedback resistor to be oversized
Solution Approach 2:
Instead of trying to reduce the non-linearity by making the resistor larger (conventional approach), the invention inverts the approach by adding a compensating element that actively counteracts the non-linearity. The compensation capacitor creates an opposing effect that cancels out the voltage coefficient, achieving harmonic improvement through compensation rather than size increase
Data Source
AI summary
A high-linearity amplifier including a main operational amplifier, a feedback circuit, and a compensation circuit is shown. The feedback circuit couples an output signal of the main operational amplifier to an input port of the main operational amplifier. The compensation circuit is coupled to the input port of the main operational amplifier to compensate for the non-linearity of the feedback circuit. A signal coupled to the input port of the main operational amplifier through the compensation circuit has an inverse phase compared to the output signal of the main operational amplifier.