Weighted-Bit RF Attenuator and Phase Shifter for Finer Resolution
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Solution Overview
Problem
Conventional 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 to achieve desired attenuation or phase shift ranges.
Innovation Solution
The use of dithering approaches to weight bits in DSA and DPS circuits, allowing for fractional intermediate steps of attenuation or phase shift, enabling higher resolution without additional cost by separating range from resolution and leveraging transmission line architectures to achieve less than 2 dB of attenuation per bit position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional binary-weighted attenuator stages are used, then the device complexity is reduced, but the measurement precision (resolution) is limited to the LSB value
Solution Approach 1:
The patent changes the parameter of bit position weights from conventional binary values (1, 2, 4, 8 dB) to non-binary weighted values that are optimized for transmission line attenuators. This allows achieving higher resolution (e.g., 0.1 dB steps) while maintaining a manageable number of stages, as the weights are specifically designed to work with the physical constraints of transmission line technology.
Solution Approach 2:
The patent segments the total attenuation range into multiple stages with specifically optimized weight values. Instead of using standard binary segmentation, each stage is assigned a weight that contributes to both the overall range and the fine resolution steps, allowing the system to achieve high precision without requiring an excessive number of segments.
2Measurement precision
If the number of attenuator stages is increased to achieve higher resolution, then the measurement precision improves, but the device complexity and cost increase
Solution Approach 1:
By changing the weight parameters of each stage from binary to optimized non-binary values, the patent achieves higher resolution with fewer stages. The specific weight values are calculated to maximize the range-to-resolution ratio, reducing the total number of stages needed compared to conventional binary-weighted designs.
Solution Approach 2:
The patent introduces dynamic bit position weighting where the weight of each bit position is optimized based on the desired performance characteristics. This dynamic optimization allows the system to adapt the weighting scheme to achieve the best possible resolution for a given number of stages, rather than being constrained by fixed binary weights.
3Device complexity
If binary-weighted control words are used, then the device complexity is minimized, but the range-to-resolution ratio is limited
Solution Approach 1:
The patent changes the control parameter scheme from standard binary-weighted control words to a customized weighting scheme where each bit position has an optimized weight value. This allows the control logic to remain relatively simple while achieving a superior range-to-resolution ratio, as the weights are specifically tailored to the transmission line attenuator architecture.
Solution Approach 2:
The optimized bit position weighting scheme serves multiple functions simultaneously: it provides the control mechanism, defines the attenuation ranges, and establishes the resolution steps. This multi-functionality reduces the need for separate control logic and simplifies the overall system while achieving high performance.
4Manufacturing precision
If transmission line attenuators with less than 2 dB attenuation per stage are used, then the manufacturing precision is improved, but the device complexity increases to maintain the desired range
Solution Approach 1:
The patent optimizes the attenuation parameter of each stage to be less than 2 dB, which is the optimal range for transmission line technology. By carefully selecting non-binary weight values that are all within this range, the patent achieves high manufacturing precision while minimizing the number of stages required through optimized weighting.
Solution Approach 2:
The patent segments the total attenuation range into multiple stages, each with optimized weight values that fall within the 2 dB or less range. This segmentation strategy, combined with non-binary weighting, allows the system to achieve the desired total range with a manageable number of precision stages, rather than requiring fewer stages with larger, less precise attenuation values.
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.