Digital Step Attenuator Using Thermometer Encoding
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Solution Overview
Problem
Current digital step attenuators based on binary weighted switchable stages suffer from high insertion loss and limited gain step accuracy due to the binary weighted attenuator architecture, which restricts their performance in controlling signal strength effectively.
Innovation Solution
The implementation of a digital step attenuator using programmable thermometer encoded attenuator stages, which include multiple programmable impedance arrays that adjust impedance monotonically to achieve precise attenuation levels, reducing insertion loss and improving gain step accuracy through a cascade of programmable thermometer encoded attenuator stages and a control circuit that generates thermometer encoded codewords for each stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If binary weighted switchable attenuator stages are used, then the attenuator can achieve digital step control, but the insertion loss increases and gain step accuracy deteriorates
Solution Approach 1:
The patent changes the encoding parameter from binary to thermometer coding. Each attenuator stage uses thermometer encoded control signals that directly correspond to the desired attenuation level, eliminating the need for binary-to-thermometer conversion and reducing transition errors. This parameter change improves gain step accuracy while maintaining low insertion loss through optimized switch configurations.
Solution Approach 2:
The attenuator is divided into multiple independently controllable stages, each with its own thermometer encoded control. This segmentation allows each stage to operate optimally with reduced insertion loss while the cumulative effect provides precise overall attenuation control. Each stage can be independently optimized for minimal loss.
2Speed
If binary weighted attenuator architecture is used, then digital step control is achieved, but the bandwidth is limited
Solution Approach 1:
The patent replaces the mechanical binary weighted switching architecture with an electronic thermometer encoded control system. This substitution enables wider bandwidth operation as the thermometer coding scheme allows for smoother transitions and reduced switching transients across a broader frequency range, while the control circuit complexity is managed through systematic encoding.
3Measurement precision
If multiple binary weighted stages are cascaded, then attenuation range is increased, but gain step accuracy deteriorates during transitions
Solution Approach 1:
The thermometer encoding scheme performs preliminary action by pre-establishing the correct control state for each attenuator stage before the actual attenuation transition occurs. This eliminates mid-transition errors that plague binary weighted systems, as each stage is already in its final desired state when the transition completes, improving accuracy across the full attenuation range.
Data Source
AI summary
A digital step attenuator with thermometer encoded attenuator stages is disclosed. In one embodiment, Embodiments disclosed in the detailed description may include a digital step attenuator, programmable thermometer encoded attenuator stages, the digital step attenuator may include a cascade of programmable thermometer encoded attenuator stages. Each stage may be provided by a programmable impedance array including a plurality of impedances arranged in parallel. The impedance of each of the plurality of each stage may change monotonically by switchably inserting or removing one of the plurality of impedances in the arrays. The control circuit may govern the attenuation level of each of the thermometer encoded accumulator stages as a function of a thermometric codeword, which controls the switches in the arrays.