Current-Feedback Amplifier Feed-Forward Capacitors for Higher Slew Rate
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Solution Overview
Problem
Current-feedback amplifiers face limitations in bandwidth and slew rate, particularly in non-inverting configurations, due to the reliance on input buffer slew rate and parasitic capacitance, which restricts output voltage slew rate and increases power dissipation.
Innovation Solution
Incorporating feed-forward capacitors in parallel with translinear elements at the non-inverting input stage of the current-feedback amplifier, forming translinear loops and improving the amplifier's configuration to enhance slew rate and reduce power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional voltage feedback or conventional current-feedback amplifier configurations are used, then the amplifier structure is simple, but the slew rate is limited by the input buffer slew rate and parasitic capacitance
Solution Approach 1:
The amplifier is divided into multiple functional stages: an input stage with translinear loops and feed-forward capacitors, a buffer stage, and an output stage. The feed-forward path is segmented from the main feedback loop, allowing independent optimization of slew rate without compromising overall stability. This segmentation enables the feed-forward capacitors to boost slew rate while the feedback loop maintains accuracy.
Solution Approach 2:
Feed-forward capacitors are introduced as intermediary elements between the input stage and the output node. These capacitors act as mediators that temporarily store and release charge to provide additional current during transient conditions, thereby increasing slew rate without requiring a larger input buffer current. The capacitors mediate between the input signal and output response, enabling faster transitions.
2Speed
If the input buffer current is increased to improve slew rate, then the slew rate increases, but the power dissipation increases
Solution Approach 1:
The feed-forward capacitors are pre-charged during normal operation through the feedback loop. During transient conditions requiring high slew rate, these pre-charged capacitors discharge to provide the necessary current boost. This preliminary charging action allows the system to have high slew rate capability without requiring continuously high input buffer current, thereby reducing average power dissipation while maintaining peak performance.
Solution Approach 2:
The invention changes the dynamic parameters of the amplifier by introducing capacitive elements that alter the current distribution. The feed-forward capacitors enable the amplifier to switch between different operating states: during transients, they provide high current for fast slewing; during steady-state, they draw minimal current. This parameter change allows high slew rate without proportionally increasing power dissipation.
3Speed
If feed-forward capacitors are added to increase slew rate, then the slew rate improves, but the device complexity increases
Solution Approach 1:
The feed-forward capacitor network is merged with the existing translinear loops in the input stage. Rather than adding completely separate circuitry, the capacitors are integrated into the existing transistor structures and biasing networks. This merging approach allows the feed-forward function to be achieved using minimal additional components, reducing the impact on overall device complexity while still providing significant slew rate improvement.
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
The implementation of feed-forward capacitors significantly increases the slew rate of the current-feedback amplifier, especially in non-inverting configurations, by allowing greater error current generation and eliminating slew-limited behavior, even at low gain conditions, without increasing input buffer current.
Implementation Method 1
In one embodiment, the current-feedback amplifier and feed-forward capacitor(s) are arranged as follows. The input stage includes two translinear loops, where each translinear loop includes a translinear element that is connected to the non-inverting input of the current-feedback amplifier. One feedforward capacitor is in parallel with each translinear element that is connected to the non-inverting input of the current-feedback amplifier.
Data Source
AI summary
A current-feedback amplifier with at least one feed-forward capacitor at the input stage of the current-feedback amplifier is provided. In one embodiment, the current-feedback amplifier and feed-forward capacitor(s) are arranged as follows. The input stage includes two translinear loops, where each translinear loop includes a translinear element that is connected to the non-inverting input of the current-feedback amplifier. One feed-forward capacitor is in parallel with each translinear element that is connected to the non-inverting input of the current-feedback amplifier. In other embodiments, the feed forward capacitor(s) are arranged in a different manner.