LNA Input Capacitance Switching to Reduce RF Signal Attenuation
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Solution Overview
Problem
CMOS wireless communication circuits face signal loss due to parasitic capacitance in the receiver circuit, which is exacerbated by the use of CMOS processes, and existing solutions like antenna switches or strip lines increase cost and board size.
Innovation Solution
A wireless communication circuit with a variable capacitance between the gate and source of the MOS input transistor in the LNA, whose capacitance value changes between transmission and reception times, forming a parallel resonant circuit during transmission to reduce load and a zero value during reception, thereby preventing signal attenuation without additional circuit elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an antenna switch is provided between the transmitter circuit and the receiver circuit to prevent signal leakage, then signal loss is reduced, but the number of circuit elements increases and cost increases
Solution Approach 1:
The invention extracts the switching function from a separate antenna switch component and integrates it into the LNA circuit itself through the variable capacitance element. This eliminates the need for a discrete antenna switch while maintaining the signal isolation function, thereby reducing the number of circuit elements and cost while preventing signal loss
Solution Approach 2:
The invention merges the switching function with the LNA input circuit by incorporating a variable capacitance element between the gate and source of the input transistor. This combination allows the LNA to perform both amplification and switching functions, reducing component count and preventing signal leakage without increasing device complexity
2Loss of energy
If a strip line is used to control the switching diode to give high impedance on the receiver side during transmission, then signal attenuation is prevented, but the board size increases
Solution Approach 1:
The invention removes the need for external strip lines by integrating the impedance control function directly into the LNA circuit through the variable capacitance element. The capacitance value change alone is sufficient to provide the necessary high impedance state during transmission, eliminating the space-consuming strip line structure while preventing signal attenuation
Solution Approach 2:
The invention changes the capacitance value of the variable capacitance element between transmission and reception modes to control the input impedance of the LNA. During transmission, the capacitance is adjusted to create high impedance and prevent signal leakage, while during reception, it returns to normal values for signal amplification, all without requiring physical space for additional strip lines
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
Attenuation of transmission and reception signals is minimized without the need for switches or strip lines, maintaining signal integrity with a reduced number of circuit elements and no increase in board size.
Implementation Method 1
the variable capacitance and the matching circuit constitute a parallel resonant circuit during the transmission time
Data Source
AI summary
A wireless communication circuit includes: an antenna; a transmitter circuit having an output amplifier outputting a transmission signal to the antenna; a receiver circuit having an LNA into which a reception signal from the antenna is input; and a matching circuit provided between the antenna and the input of the LNA. The LNA has a MOS input transistor receiving at its gate the reception signal from the antenna via the matching circuit, and includes a variable capacitance provided between the gate and source of the input transistor, the capacitance value of the variable capacitance being changed between the transmission time and the reception time.