Amplifier Oscillation Prevention via Phase Shifted Return Current
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Solution Overview
Problem
Gate-grounded and source-grounded amplifiers tend to oscillate at specific frequencies due to positive feedback, and while notch filters can prevent oscillation, they cause power loss and reduce gain in the affected frequency band.
Innovation Solution
Incorporating a phase shifter between the drain and gate electrodes of transistors in a multistage amplifier configuration, which shifts the phase of return currents by more than 90 degrees and less than 270 degrees relative to the input signal, preventing oscillation without using filters and maintaining gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a notch filter is used to prevent amplifier oscillation, then oscillation is suppressed, but power loss increases and gain decreases in the attenuated frequency band
Solution Approach 1:
The patent introduces a return current path as an intermediary mechanism to prevent oscillation. Instead of using a notch filter that directly attenuates signals, the invention creates a separate return current path with a phase shifter that generates negative feedback to counteract the oscillation-causing positive feedback, thereby preventing oscillation without attenuating the main signal path and avoiding power loss.
Solution Approach 2:
The patent employs feedback by creating a return current path that feeds back to the gate electrode. The phase shifter in this return path adjusts the phase of the return current to create negative feedback (phase difference between 90 and 270 degrees), which counteracts the positive feedback causing oscillation. This feedback mechanism suppresses oscillation without the power loss associated with notch filters.
2Reliability
If a notch filter is used to prevent amplifier oscillation, then oscillation is suppressed, but gain in the predetermined frequency band decreases
Solution Approach 1:
The return current path acts as an intermediary that prevents oscillation without affecting the main signal path. By separating the oscillation control function into a distinct return current path with a phase shifter, the invention maintains full gain in the amplification band while suppressing oscillation through negative feedback mechanisms.
3Power
If gate-grounded or source-grounded amplifier configuration is used, then amplification is achieved, but oscillation occurs at predetermined frequency due to positive feedback
Solution Approach 1:
The patent applies feedback by introducing a return current path that provides negative feedback to counteract the positive feedback causing oscillation. The phase shifter in the return path ensures the feedback current has a phase difference between 90 and 270 degrees relative to the input signal, creating negative feedback that suppresses oscillation while maintaining the amplification function.
Solution Approach 2:
The return current path serves as an intermediary mechanism that decouples the amplification function from the oscillation control function. This separate path with phase control allows the amplifier to maintain its gain while independently managing oscillation through negative feedback, thereby improving stability without sacrificing amplification performance.
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 approach effectively prevents amplifier oscillation while maintaining stable gain across frequency bands, reducing power loss and ensuring stable operation without the need for notch filters.
Implementation Method 1
a first capacitor that is disposed between the first control electrode of the first transistor and the reference potential line
Implementation Method 2
a first phase shifter configured to shift a phase of a first return current such that the phase of the first return current which flows from the second main electrode of the first transistor to the first control electrode of the first transistor via the reference potential line and the first capacitor has a phase difference, which is greater than 90 degrees and less than 270 degrees, from the phase of the first input signal
Data Source
AI summary
An amplifier includes: a first transistor that includes a first main electrode, a second main electrode, and a first control electrode, a first input signal being input to the first main electrode, a first output signal being output from the second main electrode; a reference potential line that is disposed on a signal line connected to the second main electrode with an insulator interposed therebetween; a first capacitor that is disposed between the first control electrode and the reference potential line; and a first phase shifter configured to shift a phase of a first return current such that the phase of the first return current which flows from the second main electrode to the first control electrode via the reference potential line and the first capacitor has a phase difference, which is greater than 90 degrees and less than 270 degrees, from the phase of the first input signal.