FET Power Amplifier Compensation for Self-Excited Oscillation
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Solution Overview
Problem
Power amplifying circuits experience self-excited oscillations due to deep negative feedback, leading to instability and large output ripple, even without input signals, necessitating a solution to suppress these oscillations and improve circuit stability.
Innovation Solution
A self-excited oscillation suppression device and method that includes a first compensation circuit connected between the drain and gate of a Field Effect Tube (FET) and a second compensation circuit in parallel with the feedback resistor, adjusting the target pole frequency and feedback gain curve to prevent oscillations by shifting the open-loop gain curve and accelerating the closure of the feedback and open-loop gain curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If deep negative feedback is applied to increase bandwidth and reduce voltage gain, then the amplifying circuit bandwidth is increased, but self-excited oscillation occurs due to phase reversal causing instability
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensation network that preemptively counteracts the phase shift caused by capacitive elements before it can cause self-excited oscillation. The compensation network includes a series combination of a resistor and capacitor connected in parallel with the feedback resistor, which generates a leading phase angle to offset the lagging phase angle from the amplifier's internal capacitances, thereby preventing oscillation before it occurs.
Solution Approach 2:
The patent employs parameter changes by adjusting the feedback network's electrical parameters (resistance and capacitance values) to modify the phase characteristics of the feedback signal. By carefully selecting the values of the compensation resistor and capacitor, the overall phase shift in the feedback loop is adjusted to remain within stable operating limits, transforming the system from an oscillatory state to a stable state while maintaining the desired bandwidth.
2Power
If multistage amplification is used to achieve higher power output, then the power amplifying capability is improved, but voltage pressurization increases causing linear distortion in open-loop state
Solution Approach 1:
The patent applies feedback by implementing a negative feedback loop that samples the output signal and feeds it back to the input through a feedback network. This feedback mechanism continuously monitors the output and adjusts the input to minimize errors, thereby reducing linear distortion and improving the accuracy of the power amplification process. The feedback ensures that the multistage amplifier operates closer to its ideal linear transfer characteristic.
3Speed
If feedback loop is closed to reduce voltage gain and increase bandwidth, then the amplifying circuit bandwidth is increased, but phase reversal occurs causing negative feedback to become positive feedback
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensation network that preemptively counteracts the phase shift caused by capacitive elements before it can cause self-excited oscillation. The compensation network includes a series combination of a resistor and capacitor connected in parallel with the feedback resistor, which generates a leading phase angle to offset the lagging phase angle from the amplifier's internal capacitances, thereby preventing oscillation before it occurs.
Data Source
AI summary
This invention relates to a self-excited oscillation suppression device and method for the power amplifying circuit, belonging to the field of electronic technology. Said power amplifying circuit includes a FET and a feedback loop. Said device includes: a first compensation circuit which is connected between a drain and a gate of the FET and a second compensation circuit which is connected in parallel with a feedback resistor of said feedback loop. It can solve self-excited oscillation caused by deep negative feedback in the existing power amplifying circuit. The first compensation circuit can shift the open-loop gain curve forward as a whole, and the second compensation circuit can speed up the closure of the feedback gain curve and the open-loop gain curve so that the two curves will close up before the self-excited oscillation; the self-excited oscillation will be suppressed, and the stability of the power amplifying circuit will be improved.