Reflection-Type Variable Attenuator with Stacked Transistors
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Solution Overview
Problem
Existing variable attenuators face challenges in achieving desired linearity, noise performance, and high-frequency operation while maintaining matched input and output ports, particularly in wireless backhaul applications where stringent signal-to-noise specifications are required.
Innovation Solution
A reflection-type variable attenuator design utilizing a hybrid module with transistors and inductances to achieve variable attenuation by controlling signal reflection, providing a high attenuation range of 3-30 dB and desirable noise and linearity performances at high frequencies, and using a stacked transistor topology for improved linearity and attenuation range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing variable attenuator topologies (current commuting VGAs, CMOS hybrid-pi attenuators, variable resistance load amplifiers) are used, then attenuation functionality is achieved, but linearity performance deteriorates
Solution Approach 1:
The patent inverts the conventional approach by using a reflection-type attenuator where the attenuated signal is obtained through signal reflection rather than direct signal path attenuation. This inversion enables superior linearity performance by utilizing the natural reflective properties of the transmission line and varactor diode, avoiding the non-linearities inherent in traditional VGA and hybrid-pi topologies.
Solution Approach 2:
The patent changes the operating parameters by using varactor diodes to dynamically adjust the resonant frequency and reflection coefficient of the attenuator. By varying the capacitance of the varactor diodes through voltage control, the attenuator achieves variable attenuation while maintaining excellent linearity across different attenuation settings, unlike fixed-topology solutions.
2Reliability
If existing variable attenuator topologies are used, then attenuation functionality is achieved, but noise performance deteriorates
Solution Approach 1:
The patent inverts the signal path approach, obtaining the attenuated signal through reflection rather than direct transmission through active components. This reflection-based approach inherently provides better noise performance as it avoids the noise generation associated with current commuting operations and active device saturation in traditional VGA and hybrid-pi topologies.
3Speed
If existing variable attenuator topologies are used, then attenuation functionality is achieved, but high frequency operation capability deteriorates
Solution Approach 1:
The patent employs varactor diodes whose capacitance can be dynamically adjusted to maintain resonant frequency alignment at different operating frequencies. This parameter adjustment capability enables the attenuator to operate effectively at high frequencies (up to and beyond the transistor transition frequency) by adapting the resonant circuit parameters to match the operating frequency, overcoming the limitations of fixed-topology attenuators.
Solution Approach 2:
The patent introduces dynamic control through voltage-variable capacitance in the varactor diodes, allowing the attenuator to adapt its resonant frequency and attenuation characteristics in real-time. This dynamic adjustment enables high-frequency operation by continuously optimizing the circuit parameters to match the operating conditions, unlike static topologies that degrade at high frequencies.
4Reliability
If existing variable attenuator topologies are used, then attenuation functionality is achieved, but input and output port matching deteriorates
Solution Approach 1:
The patent designs the reflection-type attenuator to simultaneously provide attenuation, impedance matching, and frequency selectivity through its resonant circuit structure. The varactor-diode-based resonant circuits serve multiple functions: they provide the attenuation mechanism while also maintaining conjugate matching at the input and output ports across the variable attenuation range, eliminating the need for separate matching networks in traditional topologies.
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 enables wide-range attenuation with excellent linearity and noise performance, maintaining perfect input and output matching, which is crucial for high-frequency wireless backhaul applications, preventing noise figure degradation and ensuring stable operation across a wide attenuation range.
Implementation Method 1
Each of the first and second reflection circuits may include a varactor diode. The amount of reflection through the first and second reflection circuits may be controlled by varying capacitances of the varactor diodes in response to control voltages
Implementation Method 2
The inductors L1 and L2 may be used to tune the parasitic capacitances of the transistors T1 and T2, so that the impedance of the reflection circuits, as seen from the reflection ports 152 and 154, are substantially resistive
Implementation Method 3
A reflection-type variable attenuator design utilizing a hybrid module with transistors and inductances to achieve variable attenuation by controlling signal reflection
Data Source
AI summary
A circuit for a reflection-type variable attenuator may include a hybrid module including an input port, an output port, a first reflection port, and a second reflection port. The hybrid module may be configured to split an incident signal received at the input port into a first and a second input signal. A first and a second reflection circuit may be coupled to the first and the second reflection ports, respectively. The first and the second reflection circuits each may include one or more transistors, and may be configured to, respectively, reflect the first and the second input signals to generate a first and a second reflected signal, which are directed to the output port to be constructively combined to form an output signal that is an attenuated replica of the incident signal. A variable attenuation may be achieved by controlling amount of reflection through the reflection circuits.