POTS CODEC Noise Shaping and Dynamic Filtering
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Solution Overview
Problem
In POTS systems, existing supply voltage feeding circuits face challenges in minimizing noise while maintaining effective battery feeding and ring functionality, often requiring complex low pass filters that can impair AC ring signals.
Innovation Solution
The implementation of a noise shaper and a low resolution DAC in combination with a low pass filter, which shifts quantization noise to higher frequencies, allowing for a simpler circuit design and reduced noise in the low frequency range, enabling effective battery feeding and ringing without the need for complex filter switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low pass filter is used to minimize line feeding noise, then noise is reduced, but the AC ring signal may be impaired or blocked
Solution Approach 1:
The patent applies dynamics by making the cut-off frequency of the low pass filter variable rather than fixed. The filter adapts its characteristics based on operational mode: during battery feeding it provides strong noise filtering, while during ringing it increases the cut-off frequency to pass AC ring signals effectively. This dynamic adjustment resolves the contradiction between noise reduction and ring signal transmission.
Solution Approach 2:
The patent changes the parameter of cut-off frequency dynamically based on operational requirements. By adjusting this critical parameter, the system can optimize performance for different functions - maintaining low noise during voice transmission while ensuring effective ring signal delivery during calling, thus resolving the fundamental conflict between these two requirements.
2Object-affected harmful factors
If a variable cut-off frequency low pass filter is used to maintain both noise filtering and ring functionality, then both functions are preserved, but circuit complexity increases
Solution Approach 1:
The patent merges the low pass filter with the DC-DC converter circuit, integrating noise filtering functionality directly into the voltage regulation architecture. This consolidation eliminates the need for separate complex variable filter circuits while maintaining both noise filtering and ring signal transmission capabilities, thus reducing overall circuit complexity.
Solution Approach 2:
The low pass filter is designed to serve multiple functions: it filters line feeding noise during battery feeding mode and simultaneously passes AC ring signals during ringing mode. This multi-functionality is achieved through dynamic cut-off frequency adjustment, allowing a single filter circuit to handle both requirements without needing separate dedicated circuits for each function.
3Object-affected harmful factors
If high resolution DAC is used to reduce quantization noise, then noise is reduced, but device complexity and cost increase
Solution Approach 1:
The patent extracts and separates quantization noise from the signal band by using a low pass filter with cut-off frequency above the signal bandwidth but below the quantization noise frequency. This extraction approach allows the use of lower resolution DACs while still achieving low noise performance in the audible range, as the quantization noise is pushed to frequencies that are filtered out or inaudible.
Solution Approach 2:
The patent changes the approach from increasing DAC resolution to adjusting the cut-off frequency parameter of the low pass filter. By optimizing this parameter, the system achieves effective noise reduction without the complexity and cost of high resolution DACs, demonstrating that parameter optimization can be more efficient than increasing component resolution.
Data Source
AI summary
A CODEC circuit for POTS system comprises a digital circuit for outputting a digital control signal having a first bit width, the digital control signal being indicative of a voltage to be applied to a POTS subscriber line pair. Further, the CODEC circuit comprises a noise shaper coupled to an output of the digital circuit for generating a noise-shaped control signal and a digital-to-analog converter coupled to an output of the noise shaper, the input of the digital-to-analog converter having a second bit width being larger than 1 and smaller than the first bit width.