Thermometer-Coded Attenuator for Monotonic Gain and Phase Continuity
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Solution Overview
Problem
Conventional attenuator designs face issues with poor monotonicity and phase discontinuity due to binary weighted switching schemes, leading to instability in gain control loops and large variations in signal phase between adjacent gain states, which are not feasible for high-volume monolithic integration applications.
Innovation Solution
The implementation of a thermometer coded attenuator network that decodes binary weighted steps into thermometer code weighted steps, ensuring monotonicity and reducing phase discontinuity by maintaining a constant signal delay across all attenuation steps, eliminating the need for elaborate trimming processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If binary weighted switching scheme is used to control signal path gain, then the attenuator can provide discrete attenuation steps, but poor monotonicity and phase discontinuity occur
Solution Approach 1:
The patent changes the control code parameter from binary to thermometer code, which fundamentally alters how attenuation steps are selected. This parameter change ensures that each increment in control code produces a monotonic increase in attenuation while maintaining constant signal delay, thereby eliminating phase discontinuity while preserving discrete attenuation capability
Solution Approach 2:
The patent introduces an intermediary conversion stage that translates binary control codes into thermometer codes. This intermediary element acts as a mediator between the control logic and the attenuator network, resolving the conflict between discrete step control and monotonic phase-continuous attenuation by transforming the control signal format
2Ease of operation
If binary weighted switching scheme is used, then discrete attenuation control is achieved, but large variations in signal phase between adjacent gain states occur
Solution Approach 1:
By changing the control code parameter from binary to thermometer code, the patent eliminates large signal phase variations between adjacent gain states. The thermometer coding scheme ensures that each attenuation step corresponds to a constant signal delay, thereby removing the harmful phase variations while maintaining discrete attenuation control
Solution Approach 2:
The patent implements a feedback mechanism where the control code is converted to thermometer code, which inherently provides feedback information about the current attenuation state. This feedback ensures that each step produces consistent phase characteristics, eliminating large phase variations between adjacent gain states
3Ease of operation
If conventional attenuator designs are used, then discrete attenuation steps are provided, but elaborate trimming processes are required
Solution Approach 1:
The patent makes the attenuator self-sufficient by using thermometer coded impedance elements that inherently provide the correct attenuation characteristics without requiring external trimming. The parallel connection of impedance elements with thermometer coding automatically ensures proper signal delay and monotonicity, eliminating the need for elaborate trimming processes during manufacturing
Solution Approach 2:
By changing from binary weighted to thermometer coded impedance elements, the patent eliminates the need for trimming. The parameter change in coding scheme fundamentally alters the attenuation mechanism to be inherently self-correcting, removing the harmful requirement for post-manufacturing trimming processes
Data Source
AI summary
Techniques are disclosed that allow for programmable attenuation using thermometer code steps. By thermometer coding the attenuator structure, monotonicity is guaranteed or otherwise greatly improved, which eliminates instability problems with automatic gain control loops and without the need for compensation or trimming. In addition, the thermometer coding technique also greatly reduces phase discontinuity between adjacent gain states.