Current Amplifier Feedback Circuit for Improved Linearity
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Solution Overview
Problem
Conventional current amplifiers experience linearity degradation due to the presence of a second current source connected between the source terminal and ground of the second differential pair, which reduces the peak amplitude of the voltage at the drain terminals of the transistors, leading to decreased linearity.
Innovation Solution
A current amplifier configuration that eliminates the second current source by using a differential inductor with a center tap terminal connected to the output of a current source, where the drain terminals of the transistors are connected to the input/output terminals of the differential inductor, and feedback circuits with specific impedance to improve linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a second current source is connected between the source terminal of each transistor in the second differential pair and ground, then the transistors can be properly biased, but the peak amplitude of the voltage at the drain terminals becomes small, causing linearity degradation
Solution Approach 1:
The patent removes the second current source from the circuit configuration. By eliminating this component, the voltage at the drain terminals can achieve larger peak amplitudes without being constrained by the voltage drop across the second current source, thereby improving linearity while maintaining proper biasing through the first current source and feedback mechanism
Solution Approach 2:
The patent employs feedback resistors connected between the gate terminal and drain terminal in each transistor of the first differential pair. This feedback mechanism stabilizes the gate-to-source voltage, reduces distortion in the dynamic range, and maintains linearity without requiring the second current source, thus resolving the contradiction between proper biasing and voltage amplitude
2Reliability
If feedback resistors are connected between gate terminal and drain terminal in the first differential pair, then distortion in the dynamic range of gate-to-source voltage is reduced, but the circuit complexity increases
Solution Approach 1:
The feedback resistors serve multiple functions simultaneously: they reduce distortion in the dynamic range of gate-to-source voltage, provide proper biasing for the transistors, and stabilize the operating point. By making the feedback network multi-functional, the patent achieves distortion reduction without proportionally increasing circuit complexity
Data Source
AI summary
A first transistor, a second transistor, a third transistor, and a fourth transistor, their source terminals being grounded, are provided. Further, a first feedback circuit connected between a gate terminal and a drain terminal in the first transistor, and having first impedance, a second feedback circuit connected between a gate terminal and a drain terminal in the second transistor, and having the first impedance, a current source for outputting a current, a first load circuit connected between the drain terminal of the first transistor and a first output terminal of the current source, and having second impedance, and a second load circuit connected between the drain terminal of the second transistor and a second output terminal of the current source, and having the second impedance are provided.