Patent ID: 7239196

Claim:
A filter circuit comprising: a transconductor for outputting an output current proportional to an input voltage; a resistor circuit network receiving the output current of said transconductor; an operational transconductance amplifier having an input terminal connected to a current output line of said resistor circuit network; and an integrating capacitor connected between an input terminal and an output terminal of said operational transconductance amplifier, wherein said resistor circuit network includes (n+1) number of branch nodes formed on a current propagation line for propagating the output current of said transconductor, n number of first resistor elements each connected between two of the (n+1) branch nodes, (n+1) number of second resistor elements having first ends connected to corresponding branch nodes, a third resistor element connected between a last branch node and a low impedance reference potential, and (n+1) number of switch circuits for connecting corresponding second ends of second resistor element to said current output line or low impedance reference potential in accordance with the corresponding bit data of (n+1) frequency characteristic setting bit data, which can be applied externally to the switch circuits, resistance values of said second and third resistor elements being set to several times the resistance value of said first resistor elements.