Spread-Spectrum Receiver Attenuation for ADC Overflow Control
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Solution Overview
Problem
Conventional spread-spectrum receivers face errors due to thermal noise and off-channel interference, particularly when using lower-bit ADCs like 12-bit ADCs, which lack sufficient dynamic range to tolerate significant off-channel interference, leading to ADC overflow and data errors.
Innovation Solution
Incorporating a variable attenuator controlled by a controller that monitors the ADC output to selectively attenuate the incoming signal, ensuring the ADC operates within its dynamic range by adjusting the signal level based on programmable threshold levels and hysteresis to prevent rapid toggling, allowing the receiver to handle negative signal-to-noise ratios and high interference levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a lower-bit ADC (e.g., 12-bit) is used to reduce hardware costs, then device complexity and cost are reduced, but the dynamic range is insufficient to tolerate off-channel interference, leading to ADC overflow and data errors
Solution Approach 1:
The patent implements a variable attenuator that dynamically adjusts the signal level based on the detected interference conditions. The attenuator can switch between different attenuation states (e.g., 0 dB, 20 dB, 40 dB) to adapt to varying interference levels, allowing the system to maintain reliable operation with a lower-bit ADC by preventing overflow during high interference conditions while preserving dynamic range during low interference conditions
Solution Approach 2:
The system changes the attenuation parameter of the signal path based on detected interference levels. By monitoring the ADC output for overflow conditions and adjusting the attenuator accordingly, the system dynamically modifies the signal level parameter to match the ADC's dynamic range capabilities, enabling reliable operation with reduced hardware bit depth
2Reliability
If the ADC dynamic range is increased to tolerate off-channel interference, then reliability is improved, but device complexity and hardware cost increase due to higher-bit ADC requirements
Solution Approach 1:
The patent introduces a variable attenuator as an intermediary component between the mixer and the ADC. This attenuator acts as a mediator that conditionally reduces the signal level before it reaches the ADC, preventing overflow during high interference conditions. This intermediary allows the use of a lower-bit ADC while maintaining the same interference tolerance that would otherwise require a higher-bit ADC
Solution Approach 2:
The system dynamically adjusts the attenuation level based on real-time detection of interference conditions. By monitoring the ADC output for signs of overflow or saturation, the system can switch the attenuator to appropriate settings, enabling reliable operation with a simpler, lower-bit ADC architecture
3Reliability
If signal attenuation is applied to prevent ADC overflow, then interference tolerance is improved, but signal level may drop below the quantization noise floor, affecting measurement precision
Solution Approach 1:
The variable attenuator is controlled dynamically based on detected interference conditions. The controller monitors the ADC output and only activates attenuation when interference levels indicate potential overflow conditions. During low interference conditions, the attenuator remains in its minimum attenuation state, preserving the full signal level and maintaining optimal signal-to-quantization-noise ratio for accurate measurement
Solution Approach 2:
The system changes the attenuation parameter conditionally based on interference detection. By monitoring signal levels and interference characteristics, the system adjusts the attenuator parameter only when necessary to prevent overflow, otherwise maintaining the parameter at its minimum value to preserve measurement precision
Data Source
AI summary
A received analog spread-spectrum signal is selectively attenuated prior to digitization, where the amount of attenuation is based on the amplitude of the digitized signal before the digitized signal is filtered to compensate for interference that may exist in the received signal. By selectively attenuating the signal only when the digitized signal is relatively large, the receiver can be implemented using a relatively small analog-to-digital converter (ADC) than would otherwise be the case for a particular signal processing application. Taking advantage of the signal-concentration characteristics of spread-spectrum receivers, embodiments of the present invention can be designed to operate with signal having negative signal-to-noise ratios at the A/D conversion step.