Analog Echo Cancellation via Digital Interpolation
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Solution Overview
Problem
Conventional echo cancellers operating in the digital domain are ineffective beyond half of the sample rate (Fs/2) and introduce unwanted high-frequency components when converting digital signals to analog, leading to increased distortion and jitter.
Innovation Solution
An echo canceller system that includes an interpolation filter operating in the digital domain to generate a second digital echo estimate signal without oversampling, which is then converted to an analog signal without adding high-frequency components, allowing effective echo cancellation up to Fs without introducing additional high-frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional echo canceller operates at sample rate Fs, then it can cancel echo signals within the frequency range 0 to Fs/2, but it introduces unwanted high-frequency components beyond Fs/2 when converting digital signals to analog
Solution Approach 1:
The patent applies preliminary action by performing echo cancellation for frequencies beyond Fs/2 in the digital domain before the DAC conversion. The echo canceller processes and cancels echo components at rates exceeding Fs, then the interpolated output is converted to analog. This prevents the DAC from adding unwanted high-frequency components since the echo cancellation is already completed in the digital domain for the extended frequency range.
Solution Approach 2:
The patent uses an interpolation filter as an intermediary between the digital echo canceller and the DAC. The interpolation filter processes the digital echo estimate signal at rates greater than Fs and generates an interpolated output that can be converted to analog without introducing harmful high-frequency components. This intermediary allows the system to benefit from both digital processing capabilities and analog output without the harmful effects of direct DAC conversion.
2Reliability
If the echo canceller operates beyond Fs/2, then it can cancel higher frequency echo components, but it increases distortion and jitter due to extra high frequency components added by the DAC
Solution Approach 1:
The system performs preliminary echo cancellation in the digital domain at rates exceeding Fs before conversion to analog. This allows the echo canceller to address higher frequency components beyond Fs/2 while maintaining signal quality, because the cancellation occurs digitally where precision is maintained without the distortion and jitter issues that would arise from analog processing or direct DAC conversion of uncanceled high-frequency echoes.
Solution Approach 2:
The interpolation filter serves as an intermediary that enables extended frequency range echo cancellation while preserving signal quality. It processes the digital echo estimate at rates greater than Fs and generates an interpolated output that can be converted to analog without introducing the distortion and jitter that would result from direct DAC conversion. This intermediary structure allows the system to achieve both extended cancellation range and maintained signal quality.
Data Source
AI summary
A method and system are described for canceling an echo signal with an echo canceller in the analog domain. In one embodiment, a system includes an echo canceller that includes an interpolation unit, operating in a digital domain, that receives a first digital echo estimate signal from an LMS unit and generates a second digital echo estimate signal without oversampling. A digital-to-analog converter (DAC) receives the second digital echo estimate signal and generates an analog echo estimate signal without oversampling. The echo canceller prevents the DAC from adding a high frequency component to the analog echo estimate signal. A subtractor adds the analog echo signal to an incoming signal having an echo signal. The subtractor generates an analog signal with reduced echo signal in the useful frequency band of the incoming signal.