Sigma-Delta Modulator Notch Shaping for Wired Spectrum Efficiency
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Solution Overview
Problem
Conventional sigma-delta modulators (SDM) in wired interconnection systems suffer from underutilization of spectrum due to vacant frequency spaces between low-pass and high-pass bands, limiting the efficiency of signal transmission.
Innovation Solution
A system incorporating a sigma-delta modulator with a modified noise transfer function featuring a frequency-domain notch at the passband, allowing for additional bandpass signals to be transmitted without overlapping with the low-pass baseband signals, thereby enhancing spectrum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional sigma-delta modulator uses a sampling frequency much higher than the Nyquist sampling frequency, then the signal can be properly sampled and reconstructed, but the spectrum has a large vacancy that is not fully utilized
Solution Approach 1:
The patent introduces a feedback circuit that creates a modifying function with zeros at specific frequencies (square root of negative one), effectively adding a frequency-domain dimension to the noise transfer function. This transforms the single-band noise shaping into a multi-band noise shaping capability, allowing simultaneous transmission of low-pass and bandpass signals in different frequency dimensions without interference
Solution Approach 2:
The patent segments the spectrum into distinct bands (low-pass band and passband) by creating notches in the noise transfer function at specific frequencies. This segmentation allows different types of signals to occupy different frequency regions independently, with the feedback circuit's modifying function creating frequency-domain partitions that prevent noise from contaminating the bandpass region
2Ease of operation
If the sampling frequency is set much higher than the Nyquist sampling frequency for practical engineering considerations, then integer multiplication of reference frequency is achieved, but the vacant spectrum between low-pass band and fs/2 cannot be utilized
Solution Approach 1:
The patent makes the wired interconnection system universally capable of transmitting multiple signal types simultaneously by introducing a feedback circuit that creates a modified noise transfer function. This single feedback mechanism enables the system to handle both low-pass baseband signals and bandpass signals in the vacant spectrum, making the oversampling architecture serve multiple functions rather than leaving spectrum vacant
3Measurement precision
If noise is shaped away from the low-pass band using conventional methods, then the low-pass signal quality is improved, but the vacant passband remains unusable for additional signals
Solution Approach 1:
The patent employs a feedback circuit that feeds back a portion of the quantized output to the input through a modifying function. This feedback mechanism dynamically adjusts the noise transfer function to create notches at specific frequencies (including the passband), thereby shaping noise away from both the low-pass band and the passband simultaneously, enabling high-quality low-pass signals while also making the passband available for additional signals
Solution Approach 2:
The patent changes the frequency-domain parameters of the noise transfer function by introducing a modifying function with specific zeros (at square root of negative one and other frequencies). This parameter modification transforms the conventional single-band noise shaping into a multi-band noise shaping capability, creating frequency-selective noise suppression that preserves both low-pass signal quality and passband availability
Data Source
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AI summary
The invention provides a sigma-delta modulator (SDM) and associated system improving spectrum efficiency of wired interconnection. The SDM may comprise a main circuit for transferring an aggregated signal by a signal transfer function, and a noise shaping circuit for shaping noise away from a low-pass band by a modified noise transfer function. A frequency response of the modified noise transfer function may have a notch at a passband, and the passband may not overlap with the low-pass band.