Bootstrapped Unity Gain Follower With Buffered Feedback Stability
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Solution Overview
Problem
Amplifier circuits with positive feedback, such as bootstrapping, face challenges in reducing input capacitance and source impedance-related errors, which can lead to reduced stability and noise performance due to uncontrolled amplifier loads.
Innovation Solution
Incorporating an additional unity gain buffer into the amplifier circuit to create a positive feedback loop that provides a bootstrap signal, reducing input capacitance and source impedance errors while maintaining stability through controlled feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If positive feedback bootstrapping is applied to increase input impedance, then input impedance is improved, but stability deteriorates due to uncontrolled amplifier loads
Solution Approach 1:
The patent introduces a buffer amplifier as an intermediary component between the bootstrapping feedback path and the amplifier load. This buffer isolates the feedback network from the variable load, preventing load variations from affecting the feedback signal and causing oscillation. The buffer acts as a mediator that allows bootstrapping to increase input impedance while maintaining system stability by decoupling the feedback loop from uncontrolled load changes.
2Stress or pressure
If positive feedback bootstrapping is applied to increase apparent resistor value, then input impedance is improved, but noise performance deteriorates
Solution Approach 1:
The buffer amplifier serves as an intermediary that prevents noise generation in the bootstrapping feedback path. By placing the buffer between the feedback network and the amplifier input, it isolates the high-impedance feedback nodes from direct coupling to the input, thereby reducing the pickup and injection of electromagnetic interference and thermal noise while preserving the input impedance enhancement benefit.
3Speed
If additional unity gain buffer is added to provide bootstrap signal, then bandwidth is improved, but device complexity increases
Solution Approach 1:
The additional unity gain buffer is designed to perform multiple functions simultaneously: it provides the bootstrap feedback signal for input impedance enhancement, acts as a voltage follower for signal buffering, and serves as an isolation element for stability control. By making this single component multi-functional, the patent achieves bandwidth improvement through enhanced input impedance without proportionally increasing overall device complexity.
Data Source
AI summary
An amplifier circuit includes an input amplifier; an output unity gain buffer; and a second unity gain buffer. The output unity gain buffer and the second unity gain buffer are each configured to receive a signal from an input amplifier. The output unity gain buffer is configured to provide an output voltage to an amplifier output, and the second unity gain buffer is configured to provide a bootstrap signal to the input amplifier. A unity gain amplifier includes an input unity gain amplifier; and an output unity gain buffer and a second unity gain buffer. The buffers are configured to receive a signal from an input amplifier. The output unity gain buffer is configured to provide an output voltage to an amplifier output, and the second unity gain buffer is configured to provide a bootstrap signal to the input unity gain amplifier.