ADSL Receiver Amplifier With Gain-Dependent Echo Filtering
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Solution Overview
Problem
In ADSL reception signal amplification, the dominant echo signal in the downstream frequency band poses a challenge for optimizing the signal-to-noise ratio, particularly in central office reception devices, as it can lead to overloading of subsequent signal processing units, and existing solutions like hybrid circuits and lowpass filtering are either technically or cost-inefficient.
Innovation Solution
A method and device that adjust gain and employ gain-dependent lowpass filtering with a variable cutoff frequency to filter out echo signals, using an amplifier with a variable resistance feedback path and parallel capacitance to adjust both gain and cutoff frequency, allowing for compact and efficient signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high gain amplification is applied in the first amplifier stage to optimize signal-to-noise ratio, then signal-to-noise ratio is improved, but subsequent analog-digital converter may be overloaded by dominant echo signal
Solution Approach 1:
The patent applies preliminary action by performing lowpass filtering before the first amplification stage to remove the dominant echo signal from the downstream frequency band. This preliminary removal of harmful frequencies prevents them from being amplified and causing overload in subsequent stages, while still allowing the first amplifier stage to provide high gain for the desired signal frequencies.
Solution Approach 2:
The patent extracts and removes the harmful echo signal components from the reception signal before amplification. By using a lowpass filter with cutoff frequency below the downstream frequency band, the dominant echo signals are separated and eliminated, allowing the amplifier to work only with the desired upstream signal frequencies.
2Object-generated harmful factors
If lowpass filtering is performed before amplification to remove echo signal, then echo signal dominance is reduced, but cutoff frequency must be set relatively low requiring large resistances and capacitances
Solution Approach 1:
The lowpass filtering is performed as a preliminary action before the main amplification stage, removing the harmful echo signals early in the signal path. This approach allows the use of moderate filter component values since the filter only needs to attenuate the downstream band, not provide the full signal conditioning that would require extremely low cutoff frequencies.
Solution Approach 2:
The patent changes the parameter of cutoff frequency to be optimized for the specific application - setting it between the upstream and downstream frequency bands rather than using a universally low value. This allows the use of practical resistance and capacitance values that fit on a chip while still effectively removing the echo signals.
3Object-generated harmful factors
If lowpass filtering with low cutoff frequency is used to filter out echo signal, then echo signal is filtered out effectively, but signal-to-noise ratio optimization becomes difficult due to fixed cutoff frequency
Solution Approach 1:
The patent applies dynamics by making the cutoff frequency of the lowpass filter variable rather than fixed. The cutoff frequency can be adjusted dynamically based on the specific signal conditions, allowing optimization of both echo rejection and signal-to-noise ratio for different operating scenarios and frequency allocations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively filters out spurious signals, maintaining a high signal-to-noise ratio even with high gain amplification, preventing overloading of subsequent units and allowing for cost-effective chip design with reduced component size and tolerance requirements.
Implementation Method 1
a gain is adjusted, in particular as a function of a signal level of the reception signal
Implementation Method 2
Lowpass filtering may be carried out before the amplification, in order to filter out the echo signal as much as possible
Implementation Method 3
using an amplifier with a variable resistance feedback path and parallel capacitance to adjust both gain and cutoff frequency
Data Source
AI summary
A method and a device for amplifying a reception signal are provided, involving the adjustment of a gain by which the reception signal is amplified, in particular as a function of a signal level of the reception signal. For example, lowpass filtering with a variable cutoff frequency is used to filter out a gain-dependent frequency range of the reception signal, which may especially contain an undesirable echo signal. Such a method and such a device are suitable in particular for the reception of ADSL signals in a central office.