RF Switch Stack Charge Control for OFF-State Voltage Droop
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Solution Overview
Problem
In RF switch stacks, undesired leakage currents during the OFF state alter the desired DC voltage distribution, leading to reduced power handling capability and increased design costs due to the need for a negative power supply.
Innovation Solution
The implementation of drain-source charge control elements in FET switch stacks, which provide local charge support by sampling RF signals at tapping points within the resistive ladders to redistribute DC voltages and counteract voltage drooping, thereby maintaining a desired DC voltage distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a negative power supply is used to maintain desired DC voltage distribution, then the power handling capability is improved, but the device complexity and cost increase
Solution Approach 1:
The charge control elements automatically detect and correct voltage drooping conditions without external intervention. The elements monitor the DC voltage distribution and activate only when needed, making the system self-regulating and eliminating the need for complex external negative power supply circuitry.
Solution Approach 2:
The invention extracts and addresses only the specific problem of voltage drooping in the drain-source resistive ladder by inserting charge control elements at strategic tapping points. This localized solution avoids the need for a comprehensive negative power supply system while still achieving the desired voltage distribution.
2Strength
If charge control elements are added to maintain DC voltage distribution, then the power handling capability is improved, but the device complexity increases
Solution Approach 1:
Charge control elements are introduced as intermediary components between the existing resistive ladder elements. These intermediaries provide the necessary charge compensation without replacing or significantly modifying the existing circuit architecture, thus minimizing overall complexity increase.
Solution Approach 2:
Rather than uniformly enhancing all parts of the circuit, charge control elements are selectively placed only at tapping points where voltage drooping occurs. This localized approach provides precise correction where needed while avoiding unnecessary complexity in other circuit regions.
3Device complexity
If bias resistors are used to distribute DC voltage, then the circuit structure is simplified, but voltage drops occur that reduce power handling capability
Solution Approach 1:
The charge control elements act as counterbalancing components that compensate for the voltage drops introduced by the bias resistors. By injecting charge at strategic points, these elements counteract the unwanted voltage reductions and restore the desired DC voltage distribution across the transistor stack.
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 enhances the power handling capability of transistors in the switch stack while reducing the need for expensive negative power supplies and minimizing voltage drops across bias resistors, thus improving overall circuit performance.
Implementation Method 1
drain-source charge control elements which provide local charge support by sampling RF signals at tapping points within the resistive ladders
Implementation Method 2
The RF signal at each point is superimposed on the existing DC voltage. When the FET switch stack is in the OFF or non-conducting state, the FET switch stack is designed to conduct no real component of current, which is current in phase with the RF voltage applied. The transistor stack appears as a purely capacitive impedance due to the series gate-drain capacitor Cgd, gate-source capacitor Cgs
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.