Digital Variable Capacitance Circuit for Low-Voltage RF Output
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Solution Overview
Problem
Existing digital variable capacitance circuits face issues with breakdown voltage and leak current when subjected to large voltage amplitudes, particularly in low power supply voltage operations, making it difficult to achieve high transmission output while using alkaline batteries.
Innovation Solution
A digital variable capacitance circuit design that includes multiple capacity cells connected in parallel, with each cell featuring a first capacitor and an NMOS transistor, where the transistor is controlled by a digital signal to adjust capacitance, allowing for voltage division and reduced voltage amplitude on the NMOS transistor, thereby preventing malfunction and enabling low power supply voltage operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a digital variable capacitance circuit uses a switching MOS transistor connected in series to the ground side of capacity cells, then the resistance value of the variable resistance element is increased, but breakdown voltage or leak current occurs when a signal having a large voltage amplitude is supplied
Solution Approach 1:
The patent introduces an impedance element (resistor or inductor) as an intermediary component connected in series between the capacity cell and the switching transistor. This intermediary element acts as a buffer that reduces the voltage amplitude applied to the transistor when the signal line is disconnected, preventing breakdown and reducing leak current while maintaining the capacitance adjustment function.
2Adaptability or versatility
If the circuit operates with low power supply voltage to improve economy, then alkaline batteries can be used, but transmission output is reduced
Solution Approach 1:
The patent changes the electrical parameters of the circuit by introducing the impedance element, which modifies the voltage distribution and current characteristics. This allows the circuit to maintain stable operation with low power supply voltage from alkaline batteries while the capacitance adjustment function compensates for transmission output variations, enabling adaptable operation across different power conditions.
3Adaptability or versatility
If the capacitance is adjusted by controlling the switching MOS transistor, then the capacitance value is variable, but the transistor malfunctions under large voltage amplitude
Solution Approach 1:
The impedance element serves as a protective intermediary that isolates the switching MOS transistor from large voltage amplitudes. When the signal line is disconnected, the impedance element limits the voltage reaching the transistor, preventing malfunction and ensuring reliable capacitance adjustment operation across all signal conditions.
Data Source
AI summary
A radio frequency integrated circuit includes an amplification circuit for outputting a radio frequency signal to an antenna, a balun including a first terminal, a second terminal, a third terminal, and a fourth terminal, and a variable capacitance circuit including a fifth terminal and a sixth terminal. The first terminal and the second terminal of the balun receive output signals of the amplification circuit. The third terminal and the fourth terminal of the balun are connected to the fifth terminal and the sixth terminal of the variable capacitance circuit, respectively, and the fifth terminal is connected to a radio frequency output terminal. The variable capacitance circuit includes a plurality of capacity cells that are connected in parallel between two output terminals.