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 (DPS) have limited resolution due to binary-weighted control words, leading to increased cost and complexity for higher accuracy in RF applications.
Innovation Solution
Employ a dithering approach to weight bits in DSA and DPS circuits, using bit position weighting functions such as linear, alternating linear, geometric, alternating geometric, harmonic, and alternating harmonic series to achieve finer resolution without additional cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If binary-weighted control words are used in conventional DSA and DPS circuits, then the circuit structure is simple, but the resolution is limited
Solution Approach 1:
The patent applies dynamics by transitioning from static binary-weighted control to dynamic dithering control. The system uses dynamic switching of attenuator stages with dither signals to achieve variable resolution, where the effective resolution changes based on the input signal amplitude and dither frequency, thereby breaking the fixed resolution limitation of binary-weighted systems without proportionally increasing circuit complexity
Solution Approach 2:
The patent changes the control parameter from simple binary weights to dither-based weighted control. By introducing dither signals and changing the control methodology from direct binary switching to dither-modulated switching, the system achieves finer effective resolution steps while maintaining a relatively simple attenuator stage structure, thus resolving the contradiction between resolution and complexity
2Measurement precision
If higher accuracy is achieved in RF applications, then the performance is improved, but the cost and complexity increase
Solution Approach 1:
The patent applies self-service by using the dithering mechanism to generate its own fine-resolution control signals internally. The dither signal is generated within the system and used to modulate the switching of attenuator stages, creating effective sub-LSB resolution steps without requiring external high-precision control circuitry, thereby achieving higher accuracy without proportional increases in cost and complexity
Solution Approach 2:
The patent uses periodic dither signals to achieve higher accuracy. By applying periodic switching with dither frequencies, the system creates effective average attenuation values that fall between the discrete binary steps, enabling higher precision control. This periodic action allows the system to achieve fine resolution through time-averaging effects rather than requiring physically finer discrete steps, thus improving accuracy without proportionally increasing complexity
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.