Amplifier Feedback Shield Layout for Parasitic Capacitance Control
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Solution Overview
Problem
Larger crosspoint switch die sizes lead to increased parasitic capacitance, limiting dynamic performance due to long signal lines and numerous circuit elements, causing issues like ringing, poor settling times, and oscillatory behavior, and require external feedback capacitors.
Innovation Solution
Incorporating shield conductors adjacent to feedback signal lines within the integrated circuit to interrupt parasitic capacitance and generate capacitance between feedback lines and output terminals, potentially eliminating the need for external feedback capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If crosspoint switch die size is increased to provide larger input and output counts, then the switch capacity and versatility are improved, but parasitic capacitance increases which degrades dynamic performance
Solution Approach 1:
A ground isolation conductor is introduced as an intermediary element between the feedback signal line and the ground plane. This conductor acts as a mediator to block the formation of parasitic capacitance between the feedback line and ground, thereby eliminating the harmful capacitive coupling while allowing the larger die size to maintain its switching capacity.
2Adaptability or versatility
If signal line length is increased to accommodate more circuit elements, then the switch functionality is improved, but parasitic capacitance increases causing ringing and oscillation
Solution Approach 1:
The ground isolation conductor serves as a mediator that interrupts the parasitic capacitance path between the feedback signal line and ground. By placing this isolation conductor adjacent to the feedback signal line, the harmful capacitive coupling is blocked, preventing ringing and oscillation while allowing the signal line to extend across the larger die to provide enhanced switch functionality.
3Reliability
If external feedback capacitors are added to combat parasitic capacitance effects, then dynamic performance is improved, but device complexity and component count increase
Solution Approach 1:
The invention converts the harmful parasitic capacitance effect into a beneficial solution by using the ground isolation conductor to block the parasitic path. This approach eliminates the need for external feedback capacitors, as the isolation conductor itself prevents the formation of harmful capacitance between the feedback line and ground, thereby improving dynamic performance without increasing component count.
Solution Approach 2:
The ground isolation conductor provides a self-service solution by inherently blocking parasitic capacitance formation through its placement adjacent to the feedback signal line. This built-in protection mechanism eliminates the need for separate external feedback capacitors, as the isolation conductor performs the capacitance-combatting function as part of its structural role in the circuit layout.
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 reduces parasitic capacitance effects, improves dynamic performance, and may allow for the omission of external feedback capacitors by utilizing internally generated capacitance, enhancing the ratio of beneficial to parasitic capacitance.
Implementation Method 1
parasitic capacitance that otherwise would be established between the feedback signal line and ground
Implementation Method 2
create a capacitance between the output terminal and the feedback signal line
Data Source
AI summary
An amplifier structure includes shield conductors that are provided spatially adjacent to elongated feedback signal lines that couple a feedback circuit to an amplifier input. The shield conductors are provided between the feedback signal lines and a ground plane, which interrupts a parasitic capacitance that otherwise would be established between the feedback signal line and ground. The shield conductors are electrically coupled to the amplifier's outputs which create a capacitance between the output terminal and the feedback signal line. In some embodiments, the capacitance generated between the output terminal and the feedback signal line can suffice as a capacitor in a feedback path of the amplifier and be contained in an integrated circuit die on which the amplifier is manufactured. Optionally, a structure may be provided that eliminates common mode signals on the feedback lines while simultaneously preserving the common mode signals on the amplifier output terminals. In this option, a second amplifier is provided that, in response to common mode variations at the output terminal, generates counterbalancing voltage variations on a second circuit that is coupled to the feedback lines at their source. The two variations cancel each other out at nodes from which the feedback lines originate, which substantially reduces feedback common mode variation even when there is common mode variation at the output terminals.