RF CMOS Switch With Parallel Gate Acceleration for Fast Switching
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Solution Overview
Problem
High power RF CMOS switches in wireless communications face limitations in switching time due to high ohmic resistors, which result in switching times ranging from several microseconds, whereas applications require times in the range of tens or hundreds of nanoseconds, and reducing gate resistors is not feasible without compromising RF insertion loss and linearity.
Innovation Solution
A switch design that includes a switching transistor, a switching resistor, and an accelerating element with a resistance smaller than the switching resistor, which is connected in parallel to the switching resistor upon switching of the transistor until a predetermined voltage is reached, reducing the RC time constant and thus the switching time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high ohmic resistors are used in the switching transistor, then RF insertion loss and linearity are improved, but switching time increases to several microseconds
Solution Approach 1:
The patent applies dynamics by making the resistance value time-dependent through the parallel combination of the switching resistor and accelerating element. During switching transitions, the accelerating element provides a low-impedance path to rapidly charge/discharge the gate capacitance. Once switching is complete, the accelerating element is disconnected or its effect diminishes, leaving the high-impedance switching resistor to maintain RF performance. This dynamic resistance adjustment resolves the contradiction between fast switching and good RF characteristics.
Solution Approach 2:
The accelerating element is activated in advance during the switching transition period to pre-charge or pre-discharge the gate capacitance before the main switching action occurs. This preliminary action reduces the time required for the switching transistor to reach its final state, thereby reducing overall switching time without requiring permanent changes to the high-impedance switching resistor that would compromise RF performance.
2Loss of time
If gate resistors are reduced to decrease switching time, then switching time improves, but RF insertion loss and linearity are compromised
Solution Approach 1:
The patent implements dynamic resistance switching where the accelerating element temporarily reduces the effective resistance during switching transitions. This allows the system to achieve low resistance benefits (fast switching) only when needed, while maintaining high resistance benefits (good RF performance) during steady-state operation. The accelerating element is connected in parallel with the switching resistor and is activated only during switching events.
Solution Approach 2:
The accelerating element is strategically placed only at the gate control terminal where it is needed to affect switching speed. This localized intervention does not alter the overall resistance characteristics of the switching transistor that affect RF performance. The accelerating element's low resistance is confined to the gate control path and does not extend to the RF signal path, thus maintaining RF insertion loss and linearity.
3Loss of time
If the accelerating element is connected in parallel to the switching resistor, then the RC time constant is reduced and switching time decreases, but device complexity increases
Solution Approach 1:
The accelerating element is merged with the existing switching resistor in a parallel configuration, allowing both components to share the same control terminal connection. This merging approach minimizes additional circuitry by utilizing the existing switching resistor structure while adding only the necessary accelerating element and control logic. The parallel combination allows the system to achieve reduced RC time constant without completely replacing the switching resistor.
Solution Approach 2:
The accelerating element acts as an intermediary component that temporarily modifies the resistance characteristics during switching transitions. It mediates between the conflicting requirements of fast switching and good RF performance by providing a low-impedance path only when needed. The control circuitry for the accelerating element serves as an intermediary mechanism that manages when this parallel path is active, minimizing the impact on overall device complexity.
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 design reduces switching time to several hundred nanoseconds without affecting RF performance or altering the semiconductor design of the switching transistors, improving switching efficiency while maintaining RF signal integrity.
Implementation Method 1
reducing the RC time constant and thus the switching time
Data Source
AI summary
A switch includes a switching transistor, a switching resistor, connected between a control terminal of the switching transistor and a switching control terminal, and an accelerating element. The accelerating element includes a resistance smaller than a resistance of the switching resistor, the accelerating element being adapted to be connected in parallel to the switching resistor upon switching of the switching transistor until a voltage at the control terminal of the switching transistor has reached a predetermined value.