Active filter circuit

An active filter circuit comprising:

• a filter circuit main part including a first conductance amplifier and a second conductance amplifier in which conductances are each proportional to currents or voltages of control input signals;
• a first signal generation circuit means for generating a current or voltage which corresponds to a first signal;
• a second signal generation circuit means for generating a current or voltage which corresponds to a second signal;
• a third signal generation circuit means for generating a current or voltage which corresponds to a third signal;
• a first control signal generation circuit for generating a first control signal in accordance with a multiplication of said first signal and a ratio of said second signal to said third signal and supplying said first control signal to said second conductance amplifier;
• and
• a second control signal generation circuit for generating a second control signal in accordance with a multiplication of said first signal and an inverse ratio of said second signal to said third signal and supplying said second control signal to said first conductance amplifier.

An active filter circuit comprising:

• a filter circuit main part including a first conductance amplifier and a second conductance amplifier in which conductances are each proportional to currents or voltages of control input signals;
• a first control signal generation circuit for providing a current or voltage in the form of a first control input signal to said first conductance amplifier, said first control input signal having a value obtained by multiplying a first variable by a second variable;
• and
• a second control signal generation circuit for providing a current or voltage to said second conductance amplifier in the form of a second control input signal, said second control input signal having a value obtained by multiplying said second variable by an inverse value of said first variable.