Echo prevention circuit having adaptive digital filter

A digital signal processing circuit comprising:

• a first input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the first input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• a first output terminal to which an output signal of the first FIR filter is output;
• a second output terminal to which an output signal of the second FIR filter is output;
• a second input terminal to which is input a subtracted signal produced by subtracting the output signal through the second output terminal from a combined signal of the output signal through the first output terminal and a second input signal on an input/output signal common line;
• an adaptive digital filter into which the output signal of the first FIR filter is input;
• a subtracter that subtracts an output signal of the adaptive digital filter from the signal through the second input terminal;
• and
• a third output terminal to which an output signal of the subtracter is output,
• wherein the adaptive digital filter has such filter coefficients that based on the output signal from the subtracter, the output signal from the third output terminal is the subtracted signal that has had the other than the second input signal removed or reduced.

A method of setting filter coefficients of an echo prevention circuit comprising:

• an input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• an input/output terminal to which an output signal of the first FIR filter is output 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 an output signal of the adaptive digital filter from an output signal of the first subtracter;
• and
• an output terminal to which an output signal of the second subtracter is output,
• the setting method which sets the adaptive digital filter to have such filter coefficients that based on the output signal from the second subtracter, the output signal from the output terminal is the output signal from the first subtracter that has had the other than the second input signal removed or reduced.

A method of setting filter coefficients of a digital signal processing circuit comprising:

• a first input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the first input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• a first output terminal to which an output signal of the first FIR filter is output;
• a second output terminal to which an output signal of the second FIR filter is output;
• a second input terminal to which is input a subtracted signal produced by subtracting the output signal through the second output terminal from a combined signal of the output signal through the first output terminal and a second input signal on an input/output signal common line;
• an adaptive digital filter into which the output signal of the first FIR filter is input;
• a subtracter that subtracts an output signal of the adaptive digital filter from the signal through the second input terminal;
• and
• a third output terminal to which an output signal of the subtracter is output,
• the setting method which sets the adaptive digital filter to have such filter coefficients that based on the output signal from the subtracter, the output signal from the third output terminal is the subtracted signal that has had the other than the second input signal removed or reduced.

A recording medium storing a program for setting filter coefficients of an echo prevention circuit comprising:

• a processor;
• an input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• an input/output terminal to which an output signal of the first FIR filter is output 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 an output signal of the adaptive digital filter from an output signal of the first subtracter;
• and
• an output terminal to which an output signal of the second subtracter is output,
• the program which causes the processor to implement a function to set the adaptive digital filter to have such filter coefficients that based on the output signal from the second subtracter, the output signal from the output terminal is the output signal from the first subtracter that has had the other than the second input signal removed or reduced.

A recording medium storing a program for setting filter coefficients of a digital signal processing circuit comprising:

• a processor;
• a first input terminal to which a first input signal is input;
• a first FIR filter into which the first input signal is input through the first input terminal;
• a second FIR filter into which the first input signal is input at the same time as into the first FIR filter;
• a first output terminal to which an output signal of the first FIR filter is output;
• a second output terminal to which an output signal of the second FIR filter is output;
• a second input terminal to which is input a subtracted signal produced by subtracting the output signal through the second output terminal from a combined signal of the output signal through the first output terminal and a second input signal on an input/output signal common line;
• an adaptive digital filter into which the output signal of the first FIR filter is input;
• a subtracter that subtracts an output signal of the adaptive digital filter from the signal through the second input terminal;
• and
• a third output terminal to which an output signal of the subtracter is output,
• the program which causes the processor to implement a function to set the adaptive digital filter to have such filter coefficients that based on the output signal from the subtracter, the output signal from the third output terminal is the subtracted signal that has had the other than the second input signal removed or reduced.