Echo Cancellation Circuit Using Digital Subtraction
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Solution Overview
Problem
Echo cancellation errors in full duplex two-way communication systems cause amplitude errors and jitter due to amplitude differences in signal paths, which are not effectively addressed by solely analog systems.
Innovation Solution
An echo cancellation circuit with a subtractor and an echo cancellation error reducing unit using A/D and D/A converters to subtract pseudo echo signals from echo signals, reducing errors by converting and processing signals to eliminate amplitude fluctuations below a threshold value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If echo cancellation is implemented solely by an analog system, then the configuration remains simple, but amplitude differences in signal paths cause echo cancellation errors that deteriorate communication quality
Solution Approach 1:
The patent changes the operational parameters of the signal processing system by introducing digital conversion stages. The A/D converter transforms the analog echo signal into digital form, allowing precise mathematical subtraction of the pseudo-echo signal. This parameter change from purely analog to hybrid analog-digital processing resolves the contradiction by maintaining configuration simplicity while dramatically improving echo cancellation accuracy through digital signal processing capabilities.
Solution Approach 2:
The patent substitutes the mechanical/analog signal processing system with a digital processing approach. Instead of relying solely on analog circuitry to cancel echoes, the system uses digital computation to subtract the pseudo-echo signal from the received signal. This substitution of digital for analog processing in the echo cancellation function resolves the contradiction by providing superior cancellation accuracy while keeping the overall system configuration relatively simple.
2Device complexity
If analog signal paths are used for echo cancellation, then the system remains simple, but load effects from signal cables cause amplitude differences that create cancellation errors
Solution Approach 1:
The patent introduces a digital signal as an intermediary between the two analog signal paths. The A/D converter creates a digital representation of one signal path, which serves as a mediator that can be precisely manipulated and subtracted from the other path. This digital intermediary allows for precise amplitude matching and cancellation without being affected by the load effects that plague direct analog path matching.
Solution Approach 2:
The patent segments the echo cancellation function into distinct processing stages: analog signal input, digital conversion, digital subtraction, and analog output. By segmenting the processing chain and isolating the precision-critical subtraction operation in the digital domain, the system achieves high amplitude matching precision while keeping each individual stage relatively simple.
3Reliability
If digital conversion is introduced to reduce echo cancellation errors, then cancellation accuracy improves, but device complexity increases
Solution Approach 1:
The patent makes the signal cable and existing analog components serve multiple functions. The signal cable continues to transmit the communication signal while also serving as the source for the pseudo-echo signal that is fed back through the D/A converter. This multi-functionality allows the system to achieve improved echo cancellation accuracy without adding completely separate signal paths or components, thereby limiting the increase in device complexity.
Solution Approach 2:
The patent creates a digital copy of the transmitted signal through the A/D converter. This digital copy (the pseudo-echo signal) is then subtracted from the received signal to cancel the echo. By using copying rather than requiring additional physical signal paths or complex analog circuitry, the system achieves high cancellation accuracy with minimal increase in device complexity.
Data Source
AI summary
An echo cancellation circuit in a full duplex two-way communication system comprising: an input/output terminal; a subtractor having a positive and a negative input terminals, in which a first transmission signal is inputted to the negative input terminal as a pseudo echo signal, the first transmission signal is inputted through an output buffer to the positive input terminal as an echo signal, the pseudo echo signal inputted to the negative input terminal is subtracted from the echo signal inputted to the positive input terminal; and a result of the subtraction is outputted; and an echo cancellation error reducing unit having a D/A converter at an input side or an output side of the subtractor.