Variable resistance circuit, operational amplification circuit, semiconductor integrated circuit, time constant switching circuit and waveform shaping circuit

An operational amplification circuit comprising:

• a variable resistance circuit;
• and
• an operational amplifier, connected with said variable resistance circuit, having an amplification factor varying with the resistance value of said variable resistance circuit, wherein
• said variable resistance circuit includes:
• serially connected N resistors, said N being integer of at least 2, and
• N switches connected in parallel with said N resistors respectively and selectively turned on or off,
• the resistance value of at least one of said resistors is different from the resistance value of another resistor, and
• the resistance value of a parasitic resistance of each of said N switches in an ON state is in proportion to or in positive correlation similar to proportion to the resistance value of the resistor connected in parallel with said switch.

A semiconductor integrated circuit receiving an output signal from an optical pickup, comprising:

• an operational amplification circuit amplifying said output signal from said optical pickup;
• and
• another circuit, wherein
• said operational amplification circuit and said another circuit are integrated into a single chip by a CMOS integrated circuit,
• said operational amplification circuit includes:
• a variable resistance circuit, and
• an operational amplifier, connected with said variable resistance circuit, having an amplification factor varying with the resistance value of said variable resistance circuit,
• said variable resistance circuit includes:
• serially connected N resistors, said N being integer of at least 2, and
• N switches connected in parallel with said N resistors respectively and selectively turned on or off,
• the resistance value of at least one of said resistors is different from the resistance value of another resistor, and
• the resistance value of a parasitic resistance of each of said N switches in an ON state is in proportion to or in positive correlation similar to proportion to the resistance value of the resistor connected in parallel with said switch.

An operational amplification circuit comprising:

• an operational amplifier;
• and
• a variable resistance circuit connected to an input terminal of said operational amplifier, wherein
• said variable resistance circuit includes:
• serially connected N resistors, said N being integer of at least 2, and
• N switches connected in parallel with said N resistors respectively and selectively turned on or off,
• the resistance value of at least one of said resistors is different from the resistance value of another resistor, and
• the resistor having the maximum resistance value is connected to said input terminal among said N resistors.

A semiconductor integrated circuit receiving an output signal from an optical pickup, comprising:

• an operational amplification circuit amplifying said output signal from said optical pickup;
• and
• another circuit, wherein
• said operational amplification circuit and said another circuit are integrated into a single chip by a CMOS integrated circuit,
• said operational amplification circuit includes:
• an operational amplifier, and
• a variable resistance circuit connected to an input terminal of said operational amplifier,
• said variable resistance circuit includes:
• serially connected N resistors, said N being integer of at least 2, and
• N switches connected in parallel with said N resistors respectively and selectively turned on or off,
• the resistance value of at least one of said resistors is different from the resistance value of another resistor, and the resistor having the maximum resistance value is arranged on the side of said input terminal among said N resistors.