Operational Amplifier Feedback Linearization for Low HD3
Find Innovative SolutionsGenerate Solutions
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, resulting in inefficient solutions that require oversized resistors, increasing circuit size without substantial harmonic improvement.
Innovation Solution
The introduction of an inverse paralleling linearization architecture, where a compensation circuit with resistors biased in an inverse manner is coupled with the feedback circuit to compensate for non-linearity, allowing for a reasonable-sized amplifier with high-linearity by using resistors with specific size ratios and configurations.
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 separate paths: one containing the feedback resistor Rf for DC biasing, and another containing the compensation resistor Rc for AC signal feedback. This segmentation allows each resistor to be optimized independently for its specific function, enabling small resistor sizes while achieving both low third-order harmonics and compact circuit area.
Solution Approach 2:
A compensation circuit is introduced as an intermediary element that generates a compensating signal to counteract the non-linear effects caused by velocity saturation in the feedback resistor. This compensation mechanism enables the use of smaller resistors while maintaining high linearity performance.
2Manufacturing precision
If the width of the feedback resistor is increased by 2N times, then the third-order harmonic HD3 is improved by N*12 dB, but the feedback resistor becomes too huge in size
Solution Approach 1:
The feedback function is divided between two resistors with different sizes and functions: Rf for DC biasing and Rc for AC feedback. This allows the system to achieve the required HD3 performance without requiring a single oversized resistor, as the compensation resistor Rc can be much smaller than traditional single-resistor designs would require.
Solution Approach 2:
The invention changes the operating parameters of the resistors by applying different biasing conditions and signal frequencies to each resistor in the segmented feedback path. This enables optimization of each resistor's effective value for its specific role, achieving superior linearity with smaller physical dimensions.
3Duration of action of moving object
If velocity saturation effect is present in the feedback resistor, then large voltage swing is affected, but odd harmonics are seriously generated
Solution Approach 1:
The compensation circuit acts as an intermediary that senses the non-linear effects caused by velocity saturation in the feedback resistor and generates a compensating signal to cancel out the resulting odd harmonics. This allows large voltage swings to be maintained without suffering from the harmful harmonic distortion.
Solution Approach 2:
The invention implements a compensation feedback mechanism where the compensation circuit continuously monitors the feedback signal and adjusts the compensating signal to counteract the non-linear effects. This feedback-based approach enables maintenance of large voltage swing capability while suppressing odd harmonic generation.
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 couples a former-stage circuit of the amplifier to the input port of the main operational amplifier to compensate for the non-linearity of the feedback circuit. The compensation circuit and the feedback circuit form an inverse paralleling linearization architecture. In the inverse paralleling linearization architecture, a resistor in the feedback circuit corresponds to a resistor in the compensation circuit which is biased in an inversed way in comparison with the corresponding resistor in the feedback circuit.