Weighted-Bit Attenuator and Phase Shifter With Fractional RF Steps
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Solution Overview
Problem
Existing digital step attenuators (DSA) and phase shifters have limited resolution, which restricts their ability to provide high accuracy in RF applications, leading to increased cost and complexity due to the need for a large number of stages and control lines.
Innovation Solution
The use of dithering approaches to weight bits in DSA and DPS circuits, allowing for higher resolution by enabling fractional intermediate steps of attenuation or phase shift, achieved through bit position weighting functions such as linear, alternating linear, geometric, alternating geometric, harmonic, and alternating harmonic series, which separate range from resolution and improve the Figure of Merit (FOM) metric.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional binary-weighted attenuator stages are used, then the device complexity is reduced, but the measurement precision (resolution) is limited to coarse steps
Solution Approach 1:
The attenuator is divided into multiple stages with different bit position weights. Instead of using traditional binary weighting (1, 2, 4, 8...), the patent segments the attenuation range into coarse stages (MSBs) and fine stages (LSBs), where each stage contributes a specific weighted amount to the total attenuation. This segmentation allows independent optimization of each stage's resolution contribution.
Solution Approach 2:
Different stages are assigned different attenuation weights based on their bit position. The MSB stages provide coarse attenuation steps while LSB stages provide fine attenuation steps. Each stage has locally optimized attenuation values that collectively achieve high overall resolution without requiring uniform fine steps across all stages.
2Measurement precision
If the number of attenuator stages is increased to improve resolution, then the measurement precision improves, but the device complexity and cost increase
Solution Approach 1:
The patent implements dynamic attenuation control where the effective resolution of each stage can be adjusted based on the control word applied. By using weighted bit positions, the system dynamically allocates attenuation precision across different stages, allowing fewer physical stages to achieve the same effective resolution that would require many more stages with uniform weighting.
Solution Approach 2:
The attenuation values of different stages are assigned specific parameter weights (bit position weights) that change the effective resolution contribution of each stage. This parameter optimization allows the system to achieve high resolution with fewer stages by strategically assigning which stages provide coarse vs. fine attenuation steps.
3Measurement precision
If uniform attenuation steps are used across all stages, then the ease of manufacture is improved, but the measurement precision is limited
Solution Approach 1:
The attenuation function is segmented into stages with different weighting responsibilities. MSB stages use simpler, larger attenuation steps that are easier to manufacture with standard components, while LSB stages use finer attenuation steps. This segmentation allows each stage to be manufactured within practical tolerances while collectively achieving high overall precision.
Solution Approach 2:
Each stage is designed with locally appropriate attenuation characteristics. The MSB stages have coarser, easier-to-manufacture attenuation values, while LSB stages have finer attenuation values. This local optimization of attenuation quality at each stage enables high overall resolution without requiring all stages to meet stringent manufacturing tolerances.
Data Source
AI summary
Digital step attenuator (DSA) and digital phase shifter (DPS) multi-stage circuit architectures that provide for high resolution. Embodiments use a dithering approach to weight bit positions to provide a much finer resolution than the lowest-valued individual stage. Bit position weights for stages are determined so as to enable selection of combinations of n bit positions that provide a desired total attenuation or phase shift range while allowing utilization of the large number of states (2n) available to produce fractional intermediate steps of attenuation or phase shift. The fractional intermediate steps have a resolution finer than the lowest-valued stage. Bit position weights may be determined using a weighting function, including weightings determined from a linear series, a geometric series, a harmonic series, or alternating variants of such series. In some embodiments, at least one bit position has a fixed value that is not determined by the bit position weighting function.