RF Switched Attenuator Fine Trimming via Variable FET On-Resistance
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Solution Overview
Problem
Existing radio-frequency (RF) attenuators face challenges in fine trimming due to the difficulty in implementing and controlling very small resistances required for precise gain adjustments, which complicates achieving precise attenuation levels without distorting the signal waveform.
Innovation Solution
A switched attenuator with a variable switch having a variable on-resistance (Ron) is introduced, comprising a series or shunt configuration, utilizing a stack of Field Effect Transistors (FETs) to independently trim the periphery of each FET for more states with minimal complexity and layout increase, eliminating the need for small value resistors and maintaining negligible output return loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If very small resistances are used for fine gain adjustment in traditional attenuator architecture, then fine trimming precision is improved, but implementation difficulty and control complexity increase
Solution Approach 1:
The patent changes the controlling parameter from resistance value to FET on-resistance (Ron) characteristics. By adjusting the gate voltage of FETs in the variable switch, the on-resistance changes continuously, enabling fine trimming of insertion loss without requiring physically small resistance values. This transforms the control mechanism from resistive to field-effect based, resolving the implementation difficulty while maintaining precision.
Solution Approach 2:
The patent replaces the traditional mechanical/resistive fine trimming approach with an electronic field-effect control mechanism. Instead of using physical small-value resistors that are difficult to implement and control, the invention uses FETs where the gate voltage controls the channel resistance, substituting a manageable electronic control system for the problematic physical component approach.
2Stability of the object's composition
If traditional attenuator architecture is used for fine gain adjustment, then signal waveform is preserved, but fine trimming capability is limited
Solution Approach 1:
The patent introduces a dynamic control mechanism using FETs where the on-resistance can be continuously adjusted by varying the gate voltage. This dynamic control enables fine trimming capability while maintaining signal waveform integrity, as the FET operates in its linear region to provide continuous resistance adjustment without introducing distortion, unlike fixed or stepped attenuator architectures.
3Measurement precision
If variable switch with variable on-resistance is used, then fine trimming of insertion loss is achieved, but device area may increase
Solution Approach 1:
The patent makes the FET stack serve multiple functions: it acts as both the main RF switch and the fine trimming mechanism. The same variable switch structure that provides switching functionality also enables continuous insertion loss adjustment through gate voltage control, eliminating the need for separate fine trimming components and reducing overall device area despite the added control capability.
Solution Approach 2:
The patent merges the switching function and fine trimming function into a single variable switch structure. The FET stack simultaneously provides RF switching and continuous resistance adjustment for fine trimming, combining what would traditionally be separate components into one integrated structure, thereby minimizing area increase while achieving precise control.
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 approach allows for efficient fine trimming of insertion loss, enabling precise gain adjustment and attenuation without signal distortion, achieving area-efficient and compact trimming solutions suitable for RF amplifiers and digitally switched attenuators.
Implementation Method 1
A fine trimming of a gain of an amplifier, or alternatively, a fine trimming of an attenuation level of an attenuator, may be achieved by independently trimming a periphery of each transistor in a stack of transistors that form one or more switches
Data Source
AI summary
A switched attenuator comprising a radio frequency input, a radio frequency output and an attenuation cell connected between the RF input and the RF output. The attenuation cell includes a variable switch with a variable on-resistance (Ron).