| 摘要 |
PURPOSE:To simplify control, to decrease the scale of hardware and to decrease a converging time by using a cascade connecting circuit comprising a subtractor and a sample-and-hold circuit in place of a random signal generator and providing additionally an interpolation filter, three polarity detectors, a correlation device, a multiplier and a switch. CONSTITUTION:In order that an adaptive digital filter 8 makes an adaptive operation, the condition is required that the probability that the polarity of a residual echo component in a difference signal (echo + reception signal - pseudo echo) being an output of a subtractor 10 is obtained accurately is not zero by a polarity detector 12. The sample-and-hold circuits SH1-SHR and a subtractor 16 are added to satisfy the condition. In this case, a switch 24 outputs an output of the subtractor 10 at the zero cross point of the reception signal and outputs an output of the subtractor 16 at other points. The correlation of outputs of the polarity detectors 23, 19 is calculated by the correlation device 20. The polarity of the difference signal and the pseudo echo appears at the output of both the detectors respectively and the correlation device 20 outputs a value corresponding to the quantity of the residual echo. Thus, the output is multiplied by 2a to form a step size and the polarity of the detector 12 is given thereto and the result is fed back to the filter 8 so as to reduce the converging time. |
