DSP Mitigation of AC-Coupling Notch Distortion
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Solution Overview
Problem
AC-coupling capacitors in broadband communication systems introduce significant distortion due to their high-pass filtering effect, which creates a moving notch in the received signal spectrum, affecting low-frequency components and requiring large capacitors that increase packaging costs and system footprint.
Innovation Solution
Implementing a communications system with a transmitter digital signal processor applying a first adaptation function and a receiver digital signal processor applying a second adaptation function to mitigate the effects of narrow-band impairment by digitally shifting frequency components away from and then back to their original locations within the signal spectrum, using techniques like frequency shifting and duplication to create a dead-zone in the analog channel's bounded spectral region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the size of AC coupling capacitors is increased to reduce the notch width, then the low-frequency distortion is reduced, but the physical size and packaging cost increase
Solution Approach 1:
The patent replaces the physical AC coupling capacitor with a digital signal processing system that performs the same high-pass filtering function. The Tx DSP applies a first adaptation function and the Rx DSP applies a second adaptation function to collectively remove the need for large physical capacitors while maintaining the desired frequency response characteristics
Solution Approach 2:
The patent changes the operating parameters of the system by moving the high-pass filtering function from the analog domain (physical capacitor) to the digital domain (DSP algorithms). This parameter change allows the system to achieve the same filtering effect without being constrained by the physical size-capacitance relationship
2Reliability
If digital signal processing adaptation functions are applied to mitigate narrow-band impairment, then low-frequency distortion is eliminated, but system complexity increases
Solution Approach 1:
The patent divides the signal processing function into two separate adaptation functions: one applied at the transmitter (Tx DSP) and one at the receiver (Rx DSP). This segmentation distributes the computational complexity across two locations rather than concentrating it in one place, making the overall system more manageable
Solution Approach 2:
The Tx DSP applies a first adaptation function that prepares the signal in advance to counteract the anticipated notch filtering effect. This preliminary action reduces the burden on the Rx DSP, as the signal has already been pre-conditioned to compensate for the high-pass filtering
Data Source
AI summary
In a communications system having an analog channel configured to convey a data signal from a transmitter to a receiver, a method of mitigating narrow-band impairment imposed by the analog channel on the data signal within a bounded spectral region of a spectrum of the data signal. A transmitter digital signal processor (Tx DSP) applying a first adaptation function to the data signal prior to transmitting the data signal through the analog channel. A receiver digital signal processor (Rx DSP) applying a second adaptation function to the data signal received through the analog channel. The first and second adaptation functions are selected to cooperatively mitigate effects of the narrow-band impairment imposed by the analog channel.