Self-adaptive trans-hybrid balance filter

• US 5,828,589 A
• Filed: 02/23/1996
• Issued: 10/27/1998
• Est. Priority Date: 02/23/1995
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Degenhardt, Achim
• Primary Examiner(s): MOISE, EMMANUEL LIONEL
• Application Number:
  US08/605,902
• Time in Patent Office: 977 Days
• Field of Search: 364/724.19, 364/724.03, 364/724.011, 364/724.2, 364/724.11-724.14, 375/103, 375/345, 375/350, 379/388-390, 379/399-404, 395/2.34
• US Class Current: 708/322
• CPC Class Codes: H03H 21/0012 Digital adaptive filters
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers

Abstract

An adaptive balance filter includes a transmission path, a reception path, and an adaptive filter having a signal output, a coefficient output for outputting filter coefficients, an error signal input, and a signal input coupled to the transmission path. There is a main filter which has a signal output, a signal input coupled to the transmission path, and a coefficient input terminal. There is also a first subtractor which has one input coupled to the reception path, another input coupled to the signal output of the main filter, and an output forming a further course of the reception path. A second subtractor has one input coupled to the reception path, another input coupled to the signal output of the adaptive filter, and an output coupled to the error signal input of the adaptive filter. A transfer device is connected between the adaptive filter and the main filter and has a control input for loading the filter coefficients of the adaptive filter into the main filter upon command of a corresponding copy signal. A transfer control device having first, second and third inputs is provided. The transfer control device ascertains echo attenuations of the adaptive filter and the main filter from the first, second and third inputs, comparing two echo attenuations with one another, and sending a corresponding copy signal to the transfer device in the event that the echo attenuation of the adaptive filter is higher than the echo attenuation of the main filter.

Claims

1. An adaptive balance filter, comprising:

a transmission path;

a reception path;

an adaptive filter having a signal output, a coefficient output for outputting filter coefficients, an error signal input, and a signal input coupled to said transmission path;

a main filter having a signal output, a signal input coupled to said transmission path, and a coefficient input for loading filter coefficients;

a first subtractor having one input coupled to said reception path, another input coupled to the signal output of said main filter, and an output forming a further course of said reception path;

a second subtractor having one input coupled to said reception path, another input coupled to the signal output of the adaptive filter, and an output coupled to the error signal input of said adaptive filter;

a transfer device being connected between the coefficient output of said adaptive filter and the coefficient input of said main filter and having a control input for loading the filter coefficients of said adaptive filter into said main filter upon an appearance of a corresponding copy signal; and

a transfer control device having first, second and third inputs, the first input being coupled to the output of said second subtractor, the second input being coupled to the one input of said second subtractor, and the third input being coupled to the output of said main filter;

said transfer control device ascertaining echo attenuations of said adaptive filter and said main filter from signals at the first, second and third inputs, comparing two echo attenuations with one another, and sending a corresponding copy signal to said transfer device in the event that the echo attenuation of said adaptive filter is higher than the echo attenuation of said main filter; and

said transfer control device having a quality comparison device and a copy control device;

said transfer control device including;

a third subtractor having one input forming the second input and another input forming the third input of said transfer control device;

a first absolute value former having an input forming the first input of said transfer control device;

a second absolute value former having an input being connected to the one input of said third subtractor;

a third absolute value former connected downstream of said third subtractor;

first, second and third logarithm modules each being connected downstream of a respective one of said first, second and third absolute value formers and each having an output;

a fourth subtractor having inputs each being connected to the output of a respective one of said first and second logarithm modules;

a fifth subtractor having inputs each being connected to the output of a respective one of said second and third logarithm modules;

first and second low-pass filters each being connected downstream of a respective one of said fourth and fifth subtractors and each having an output; and

a sixth subtractor having inputs being connected to the outputs of said first and second low-pass filters, and an output supplying a quality difference signal;

said copy control device having an input being coupled to the output of said sixth subtractor, for comparing the quality difference signal with a first comparison value and generating a copy signal for said transfer device if the quality difference signal and the first comparison value differ in a certain direction, the first comparison value being set equal to a current value of the quality difference signal.

2. The balance filter according to claim 1, including:

a first form filter connected between the one input of said second subtractor and said reception path;

a second form filter having a transmission behavior being identical to said first form filter and being connected between said transmission path and the signal input of said adaptive filter; and

a third form filter having a transmission behavior being identical to said first form filter and being connected between the output of said main filter and the third input of said transfer control device.

3. The balance filter according to claim 1, including a third low-pass filter connected downstream of said sixth subtractor.

4. The balance filter according to claim 1, wherein said transfer control device includes:

devices for ascertaining a power of a transmitted signal present at the input of said adaptive filter and a power of a reception signal present at the one input of said second subtractor; and

an enable device connected downstream of said devices for ascertaining the transmission and reception power, for outputting an enable signal to said copy control device to enable the copy signal whenever the transmission power signal exceeds a first reference value and a difference between the transmission power signal and the reception power signal exceeds a second reference value.

5. The balance filter according to claim 4, wherein the enable signal is also delivered to said adaptive filter;

and said adaptive filter does not adapt until the enable signal appears.

6. The balance filter according to claim 1, wherein said transfer control device has an operating mode recognition device for evaluating a signal at the input of said adaptive filter for broad bandedness and narrow bandedness, and for supplying an enable signal for said copy control device upon the presence of a wideband signal.

7. The balance filter according to claim 6, wherein said operating mode recognition device includes:

a filter bank being triggered with the input signal of said adaptive filter and having a plurality of frequency band-specific outputs;

further absolute value formers connected downstream of the outputs of said filter bank;

further low-pass filters being connected downstream of said further absolute value formers and having outputs;

a mean value former being connected to the outputs of said low-pass filters and having an output;

a constant multiplier being connected downstream of the output of said mean value and having an output; and

an evaluation device connected to the output of said constant multiplier and to the outputs of said low-pass filters, for comparing various frequency band-specific signals present at the outputs of said low-pass filters with a comparison signal output by said constant multiplier and outputting a bandwidth signal if the comparison signal is exceeded by a maximum of two frequency-specific signals.

8. The balance filter according to claim 7, including:

a comparator having one input receiving a quality signal, another input receiving an attenuation reference signal corresponding to a given echo attenuation, and supplying an output signal; and

a decision element linking the bandwidth signal and the output signal of said comparator to one another for supplying an enable signal for said copy control device in the presence of a bandwidth signal corresponding to a wide bandedness of the signal at the output of said adaptive filter and in the presence of an output signal of said comparator corresponding to a certain echo attenuation.

9. The balance filter according to claim 1, wherein:

a) if the enable signal is absent, said copy control device;

resets an internal counter,

generates a copy control signal for copying the coefficients of said adaptive filter to said main filter,

sets the output signal of said second low-pass filter to be equal to the quality signal, and

sets a maximum value variable to be equal to the quality signal; and

otherwise

b) if the first enable signal is absent, said copy control device;

resets the internal counter; and

otherwise

c) if the output signal of said first low-pass filter is greater than the maximum value variable, said copy control device;

resets the internal counter,

generates a copy control signal for copying the coefficients of said adaptive filter to said main filter,

sets the output signal of said second low-pass filter to be equal to the quality signal, and

sets the maximum value variable to be equal to the quality signal; and

otherwise,

d) if the quality difference signal is greater than a quality parameter, said copy control device;

resets the internal counter,

generates the copy control signal,

sets the output signal of said second low-pass filter to be equal to the quality signal, and

sets the maximum value variable to be equal to the quality signal.

10. The balance filter according to claim 9, wherein, otherwise:

e) if the quality difference signal is greater than zero and the quality signal is greater than a limit value parameter, and

i) if a counter state is greater than a time parameter, said copy control device;

resets the internal counter,

generates the copy control signal,

sets the output signal of said second low-pass filter to be equal to the quality signal, and

sets the maximum value variable to be equal to the quality signal, and

ii) in other cases, said copy control device;

resets the internal counter, and otherwise

f) resets the counter.

11. The balance filter according to claim 1, wherein the balance filter is at least partially realized in the form of a suitably programmed data processing system.