RF Switch Stack Charge Control for OFF-State Voltage Balance
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Solution Overview
Problem
RF switch stacks experience undesired leakage currents during the OFF state, leading to voltage distribution imbalances and reduced power handling capabilities due to body leakage currents, which complicates the application of desired DC voltages and increases design costs.
Innovation Solution
Incorporating drain-source charge control elements with tapping points in the resistive ladders to locally generate charges and redistribute DC voltages, thereby reducing voltage drops and improving the DC voltage distribution across the switch stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If drain-source resistive ladder is used to bias the FET switch stack, then the RF voltage can be distributed evenly among the transistors, but body leakage currents generate undesired voltage drops that alter the DC voltage distribution
Solution Approach 1:
Charge control elements are introduced as intermediary components between the drain-source resistive ladder and the transistor drain terminals. These elements actively compensate for the voltage drops caused by body leakage currents by injecting compensating charges, thereby maintaining the desired DC voltage distribution without requiring changes to the resistive ladder structure itself.
Solution Approach 2:
The charge control elements are controlled by control voltages derived from the RF signal itself, enabling the system to automatically compensate for leakage current effects without external intervention. The RF signal modulates the charge control elements to maintain proper DC biasing conditions dynamically during operation.
2Strength
If the gate voltage is made more negative relative to drain/source voltage to increase power handling capability, then the transistor can block higher voltages, but it becomes difficult to apply the desired DC voltages to every transistor in the stack
Solution Approach 1:
The drain-source biasing network is segmented into multiple independent sections, each with its own charge control element and control voltage source. This allows each transistor in the stack to have independently optimized DC voltage conditions, enabling different transistors to operate at different bias points tailored to their specific power handling requirements.
Solution Approach 2:
The invention enables dynamic adjustment of DC bias parameters by using RF signal-derived control voltages to modulate the charge control elements. This allows the DC voltage distribution to be optimized for maximum power handling capability while maintaining proper biasing conditions across all transistors in the stack.
3Stability of the object's composition
If larger resistors are used in the drain-source resistive ladder to reduce current draw, then the voltage distribution becomes more stable, but the RF performance and power handling capability deteriorate
Solution Approach 1:
Charge control elements serve as active intermediaries that compensate for the limitations of using larger resistors. By injecting compensating charges at strategic points in the resistive ladder, these elements maintain stable DC voltage distribution while preventing the RF performance degradation that would otherwise result from the increased resistance values.
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 solution effectively reduces the impact of body leakage currents on voltage distribution, enhancing the power handling capabilities of RF switch stacks while maintaining circuit performance and reducing design costs.
Implementation Method 1
Incorporating drain-source charge control elements with tapping points in the resistive ladders to locally generate charges and redistribute DC voltages
Data Source
AI summary
Methods and devices to address the undesired DC voltage distribution across switch stacks in OFF state are disclosed. The disclosed devices include charge control elements that sample the RF signal to generate superimposed voltages at specific points of the switch stack biasing circuit. The provided voltages help reducing the drooping voltages on drain/source/body terminals of the transistors within the stack by supplying the current drawn by drain/source terminals of the stacked transistors and/or by sinking the body leakage current exiting the body terminals of such transistors. Methods and techniques teaching how to provide proper tapping points in the biasing circuit to sample the RF signal are also disclosed.