Capacitive RF Attenuator for Constant Input Impedance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing radio frequency signal attenuators face challenges in maintaining constant input impedance and achieving regular attenuation steps due to parasitic capacitance and resistance from transistors, leading to noisy signals and reduced signal excursion.
Innovation Solution
A radio frequency signal attenuator comprising multiple units with specific capacitance values and a selector mechanism, where each unit includes a first capacitor between input and output nodes and a second capacitor between output and reference nodes, with a third capacitor connecting the last unit's output to the reference, ensuring constant input impedance and controlled attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional transistors are used to control attenuation, then variable attenuation control is achieved, but parasitic capacitance and resistance cause non-constant input impedance and noisy signals
Solution Approach 1:
The patent extracts and removes the harmful parasitic elements (transistor capacitance and resistance) from the signal path by replacing the conventional transistor-based attenuator with a capacitor-based network controlled by ideal switches, thereby eliminating the source of noise and impedance variation
Solution Approach 2:
The patent changes the fundamental operating parameters by using capacitor ratios instead of resistor ratios to determine attenuation, and by using switch positioning rather than transistor conduction states, thereby achieving attenuation control without introducing parasitic effects
2Power
If conventional attenuators are used, then signal attenuation is achieved, but input impedance varies with attenuation setting
Solution Approach 1:
The patent changes the impedance-determining parameters from transistor on-resistances and parasitic capacitances to fixed capacitor values and switch positions, ensuring that the input impedance remains constant regardless of the attenuation setting
Solution Approach 2:
The patent maintains equipotential relationships through the capacitor network configuration, where the input impedance remains constant at all attenuation settings due to the fixed capacitive dividers and ideal switch architecture
3Power
If transistor-based attenuators are used, then attenuation control is achieved, but signal noise increases and signal excursion decreases
Solution Approach 1:
The patent extracts and removes the noise-generating transistor elements from the circuit, replacing them with passive capacitors and ideal switches that do not introduce thermal noise or signal degradation
Solution Approach 2:
The patent converts the potentially harmful effect of using active devices into a benefit by demonstrating that passive capacitor-based attenuation with ideal switch control eliminates noise while maintaining attenuation functionality
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 radio frequency signal attenuator with constant input impedance and regular attenuation steps, reducing noise and signal excursion, suitable for low-power communication applications like NFC and Bluetooth low energy, without introducing thermal noise or DC consumption.
Implementation Method 1
a first capacitor, connected between an input node of the unit and an output node of the unit, and a second capacitor, connected between the said output node and a reference node
Data Source
AI summary
An embodiment attenuator includes a plurality of circuits coupled in series. A respective circuit includes a first capacitor connected between an input node of the respective circuit and an output node of the respective circuit, and a second capacitor connected between the output node of the respective circuit and a reference node. The output node of the respective circuit, other than a last circuit of the plurality of circuits, is connected to the input node of a successive circuit. The attenuator further includes a plurality of selectors, in which the respective circuit is associated with a respective selector that is coupled between the output node of the respective circuit and an output node of the attenuator.