Patent ID: 7400278
Filing Date: 2008-07-15
Classification: H04M

Abstract:
1. An echo prevention circuit comprising: a filter that is inputted with a first digital signal, the filter outputting second and third digital signals; a first DA converter that converts the second digital signal into a first analog signal and outputs the first analog signal; a second DA converter that converts the third digital signal into a second analog signal and outputs the second analog signal; an input/output terminal that outputs the first analog signal or that is inputted with a third analog signal; a subtracting circuit that outputs a fourth analog signal acquired by subtracting the second analog signal from a signal generated by combining the first analog signal and the third analog signal; an amplification circuit that amplifies the signal output from the subtracting circuit and outputs the amplified signal; an AD converter that converts the signal output from the amplification circuit into a digital signal and outputs the digital signal; a response signal acquiring unit that inputs a first signal to the first DA converter to acquire a first response signal from the input of the first DA converter to the output of the AD converter, the response signal acquiring unit inputting a second signal to the second DA converter to acquire a second response signal from the input of the second DA converter to the output of the AD converter; and a filter coefficient setting unit that sets filter coefficients to the filter based on the first and second response signals such that the fourth analog signal becomes a signal generated by removing or attenuating the first analog signal from the signal generated by combining the first analog signal and the third analog signal, the amplification circuit setting a gain to a first gain in response to a first control signal input before acquiring the first and second response signals, the amplification circuit setting the gain to a second gain larger than the first gain in response to a second control signal input after acquiring the first and second response signals.