| 摘要 |
PURPOSE:To control the low and high sound frequencies of an audio signal symmetrically without changing the filter characteristic by converting an output of an LPF circuit and an HPF circuit into a current and using the current so as to control the feedback type amplifier having an inverting input and a noninverting input. CONSTITUTION:An input signal Vi is given to a noninverting input of an operational amplifier 41, the LPF 42 and the HPF 43 via a resistor Ri from an input terminal 1 and an output signal V0 is extracted from an output terminal 2. The output of the LPF 42 is inputted to voltage-current converters 44, 45, and are converted to outputs with currents multiplied by gm(1-KB) and gm(1+KB), respectively, where gm is the mutual conductance and KB is a coefficient controlling the low sound frequencies. Moreover, the output of the HPF 43 is inputted to converters 46, 47, and are converted to current outputs multiplied by the factors ga(1-KT) and ga(1+KT), respectively, where KT is a coefficient controlling the high sound frequencies. |
