Switchable Capacitive Elements Using Positive Biasing
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Solution Overview
Problem
Existing switchable capacitive elements require negative voltage sources and excessive bias swings, leading to complexity and lossiness, which degrade performance and require high-quality factor (Q factor) at RF frequencies.
Innovation Solution
A switchable capacitive element with a field effect transistor (FET) device stack and two capacitors, where the FET devices are biased using a control circuit that eliminates the need for negative voltage sources and reduces bias swings, allowing the FET device stack to operate in open and closed states with improved power handling and Q factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a negative voltage source is used to bias the gate contacts during the open state, then the FET device stack can be reliably kept off, but the circuit complexity increases and lossiness increases
Solution Approach 1:
The patent extracts and removes the negative voltage source from the control circuit. Instead of using a negative voltage source to bias the gate contacts during the open state, the invention uses only a DC voltage source that provides a positive voltage, thereby eliminating the complexity and lossiness associated with negative voltage generation while maintaining reliable FET off state through alternative biasing arrangements
Solution Approach 2:
The patent inverts the traditional biasing approach by not using a negative voltage to turn off the FET devices. Instead, it uses a positive voltage source with a different switching configuration that achieves the same off-state reliability without requiring negative voltage generation circuitry
2Reliability
If excessive bias swings are used to switch the FET device stack between open and closed states, then reliable switching is achieved, but the Q factor decreases and power performance degrades
Solution Approach 1:
The patent changes the biasing parameters by eliminating the need for large voltage swings. Instead of excessive bias swings, the invention uses a controlled positive voltage from a DC source that achieves reliable switching with smaller, more efficient voltage transitions, thereby reducing power loss and improving Q factor
3Reliability
If a negative voltage source is used for biasing, then proper FET operation is achieved, but the Q factor at RF frequencies decreases
Solution Approach 1:
The patent removes the negative voltage source that was causing Q factor degradation at RF frequencies. By using only a positive DC voltage source and reconfiguring the switching arrangement, the invention eliminates the lossy negative voltage generation circuitry while maintaining proper FET operation reliability
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 solution provides a higher Q factor and better power performance by eliminating the need for negative voltage sources and reducing bias swings, resulting in improved RF signal handling capabilities.
Implementation Method 1
a field effect transistor (FET) device stack (34), where the FET devices (32) are biased using a control circuit (48)
Data Source
AI summary
Switchable capacitive elements are disclosed, along with programmable capacitor arrays (PCAs). One embodiment of the switchable capacitive element includes a field effect transistor (FET) device stack, a first capacitor, and a second capacitor. The FET device stack is operable in an open state and in a closed state and has a plurality of FET devices coupled in series to form the FET device stack. The first capacitor and the second capacitor are both coupled in series with the FET device stack. However, the first capacitor is coupled to a first end of the FET device stack while the second capacitor is coupled to a second end opposite the first end of the FET device stack. In this manner, the switchable capacitive element can be operated without a negative charge pump, with decreased bias swings, and with a better power performance.