Adaptive Digital Filter Echo Prevention Circuit
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Solution Overview
Problem
Existing echo prevention circuits in communication devices, such as cellular telephones, struggle to accurately cancel echoes due to inaccuracies in setting circuit constants and adjusting gain and phase, resulting in insufficient echo cancellation, especially with weak voice signals.
Innovation Solution
An echo prevention circuit incorporating a first and second FIR filter, an adaptive digital filter, and subtracters to process input signals, with adaptive filter coefficients set to cancel out echo signals effectively, utilizing a method that includes acquiring impulse responses to determine optimal filter coefficients for echo cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If circuit constants are set highly accurately to cancel echo, then echo cancellation performance is improved, but manufacturing precision requirements increase and device complexity increases
Solution Approach 1:
The patent implements adaptive digital filters with dynamically adjustable filter coefficients that can be modified in real-time based on acoustic environment measurements. This replaces the static, precision-critical circuit constants with adaptive parameters that automatically adjust to compensate for manufacturing variations and environmental changes, thereby improving echo cancellation without requiring high manufacturing precision
Solution Approach 2:
The system changes the operational parameters (filter coefficients) of the digital signal processing components based on measured acoustic characteristics. By using impulse response measurements to determine optimal filter coefficients, the system adapts to actual acoustic conditions rather than relying on fixed circuit constants, resolving the contradiction between performance and manufacturing precision
2Reliability
If gain and phase are adjusted precisely to generate canceling signal, then echo cancellation is improved, but device complexity and adjustment difficulty increase
Solution Approach 1:
The adaptive digital filter system performs self-adjustment by automatically measuring the acoustic impulse response and computing optimal filter coefficients without requiring manual gain and phase adjustment. The system serves itself by adapting to the acoustic environment, eliminating the need for complex manual calibration procedures
Solution Approach 2:
The system uses feedback from impulse response measurements to automatically adjust filter coefficients. By measuring the actual acoustic path and using this information to adjust the canceling signal, the system achieves accurate echo cancellation without manual intervention, resolving the ease of operation issue
3Illumination intensity
If amplifier is provided to amplify weak voice signals, then voice audibility is improved, but echo from amplified signal increases
Solution Approach 1:
The system performs preliminary echo cancellation by generating and subtracting the expected echo signal before the amplified voice signal is output. By anticipating and removing the echo component in advance, the system can safely amplify the voice signal without creating problematic echoes, thus resolving the contradiction between voice audibility and echo prevention
Data Source
AI summary
An echo prevention circuit comprises a first and second FIR filters into which a first input signal is input through an input terminal; an input/output terminal to which an output signal of the first FIR filter is output and the output signal reflected is input or a second input signal is input; a first subtracter that subtracts an output signal of the second FIR filter from a combined signal of the output signal of the first FIR filter and the second input signal; an adaptive digital filter into which the output signal of the first FIR filter is input; a second subtracter that subtracts the output of the adaptive digital filter from the output of the first subtracter. The adaptive digital filter has such filter coefficients that based on the output of the second subtracter, the output signal from the output terminal is the output from the first subtracter that has had the other than the second input signal removed.