Spread-Spectrum Signal Conversion for High Dynamic Range
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Solution Overview
Problem
Current signal conversion systems face challenges in achieving high dynamic range and resolution while maintaining cost-effectiveness, as they require highly linear components to handle large signals and suppress noise, leading to increased complexity and expense.
Innovation Solution
The implementation of a signal conversion system that spreads input signals using direct sequence spread spectrum (DS-SS) or combined DS-SS and frequency hopped spread spectrum (FH-SS) codes before conversion, reducing linearity requirements and enabling lower dynamic range devices by distributing signal amplitudes over a wider bandwidth, which are then despread to recover the original signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high dynamic range and resolution are achieved through highly linear components, then signal conversion performance is improved, but system cost and complexity increase dramatically
Solution Approach 1:
The signal processing function is segmented into three distinct stages: spreading (modulating the input signal with a high-rate code), conversion (analog-to-digital or digital-to-analog conversion at lower dynamic range requirements), and despreading (demodulating to recover the original signal). This segmentation allows each stage to operate with relaxed linearity requirements compared to traditional direct conversion systems.
Solution Approach 2:
The system changes the temporal parameters of the signal by spreading it over a longer duration using a pseudorandom code sequence. This time-domain expansion distributes the signal energy, reducing peak amplitudes and allowing lower dynamic range converters to achieve the same effective resolution after despreading correlates the energy back to the original signal duration.
2Reliability
If highly linear components are used to suppress spurious signals and noise, then dynamic range performance is improved, but component cost increases
Solution Approach 1:
The system converts the potentially harmful effect of non-linear distortion into a beneficial feature. By spreading the signal before conversion, any non-linear distortion products generated in the conversion process are also spread and appear as low-level noise across the bandwidth. The despreading process then concentrates the desired signal while the distortion products remain dispersed, effectively suppressing their impact on dynamic range performance.
Solution Approach 2:
The spreading code acts as an intermediary that modulates the input signal, transforming it into a spread spectrum signal that can be processed by lower quality converters. This intermediary transformation allows the use of cost-effective, less linear components while maintaining high dynamic range performance through the correlation property of the spreading code during despreading.
3Reliability
If signal amplitude range is increased to handle large signals, then dynamic range upper bound is improved, but small signal resolution deteriorates due to quantization noise
Solution Approach 1:
The spreading code operates as a periodic (or pseudoperiodic) sequence that modulates the signal amplitude. This periodic modulation spreads the signal energy across time, reducing instantaneous amplitude requirements. The correlator in the despreading stage uses the known periodic structure of the code to coherently integrate the spread signal, recovering small signals that would otherwise be lost in quantization noise while maintaining the ability to handle large signals through the same spreading process.
Data Source
AI summary
Systems and methods for signal conversion are provided. Signals are spread in a continuous spectrum by a spread spectrum signal, such as a direct sequence spread spectrum (DS-SS) signal. The signals are then processed, which may include but is not limited to analog-to-digital conversion, digital-to-analog conversion, frequency conversion, clipping, filtering or a plurality of processes. The processed signal is then despread using substantially the same spreading signal that was used to spread the signal.