Cascaded Digital Step Attenuator With Low Phase Shift
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Solution Overview
Problem
Existing digital step attenuators (DSAs) face challenges in providing low phase shift across a range of attenuation steps, as they often result in significant phase differences between bypass and attenuation modes, affecting the performance of RF systems in wireless devices and base stations.
Innovation Solution
The implementation of a digital step attenuator with a cascade arrangement of stages, each capable of operating in attenuation or bypass mode, utilizing an attenuation control circuit, phase compensation capacitors, and a phase compensation inductor to minimize phase shift across attenuation steps, and incorporating a T attenuator configuration with shunt and bypass switching circuits for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a digital step attenuator uses a bypass switching circuit to achieve low attenuation steps, then the attenuation precision is improved, but a significant phase difference is introduced between the bypass mode and attenuation mode
Solution Approach 1:
The patent introduces phase compensation capacitors as intermediary elements that mediate between the bypass switching circuit and the signal path. These capacitors are specifically designed to compensate for the phase difference introduced by the bypass switch, thereby maintaining both precise attenuation control and consistent phase characteristics across different attenuation steps.
Solution Approach 2:
The patent modifies the electrical parameters of the bypass switching circuit by adding phase compensation capacitors with specific capacitance values. This changes the impedance and phase characteristics of the bypass path to match the attenuation path, eliminating the harmful phase difference while preserving the precise attenuation capability.
2Object-affected harmful factors
If phase compensation capacitors are added to compensate for phase difference, then the phase performance is improved, but the device complexity increases
Solution Approach 1:
The patent applies phase compensation capacitors locally at specific critical points in the circuit where phase difference is most problematic, rather than uniformly across the entire attenuator. This targeted approach provides effective phase compensation while minimizing the overall increase in device complexity.
Solution Approach 2:
The patent implements phase compensation using a limited number of capacitors with specific values that provide sufficient compensation for the phase difference without over-compensating. This partial action approach achieves the necessary phase performance improvement while avoiding excessive circuit complexity.
3Adaptability or versatility
If multiple attenuation stages are used to achieve a wide range of attenuation steps, then the attenuation range is improved, but the cumulative phase shift increases
Solution Approach 1:
The patent divides the overall attenuation function into multiple independent stages, each with its own phase compensation capacitors. This segmentation allows each stage to be compensated independently, preventing the cumulative phase shift that would occur in a single-stage design while maintaining the wide attenuation range through the combination of multiple stages.
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 configuration enables low phase shift and improved phase performance across a range of attenuation steps, enhancing the digital controllability and linearity of RF signals in wireless devices and base stations, while balancing bandwidth and phase shift considerations.
Implementation Method 1
one or more phase compensation capacitors configured to compensate for a phase difference between a first signal path through the attenuation circuit and a second signal path through the bypass switching circuit
Implementation Method 2
The bypass switching circuit includes a phase compensation inductor configured to further compensate for the phase difference between the first signal path and the second signal path
Data Source
AI summary
Apparatus and methods for digital step attenuators are provided herein. In certain configurations, a digital step attenuator (DSA) includes a plurality of DSA stages arranged in a cascade between an input terminal and an output terminal. Each of the DSA stages can be operated in an attenuation mode or in a bypass mode. The DSA further includes an attenuation control circuit, which can be used to control the modes of operation of the DSA stages. The attenuation control circuit can be used to operate the DSA over a plurality of attenuation steps, which can be digitally selectable. To provide low phase shift across the range of attenuation steps, a DSA stage can include one or more phase compensation capacitors used to provide low phase shift and to compensate for a phase difference between the DSA stage operating in the bypass mode and in the attenuation mode.