Variable resistance circuit, operational amplification circuit and semiconductor integrated circuit

A variable resistance circuit that has a variable resistance value being gradually variable, comprising:

• a resistance circuit including a plurality of resistors serially connected;
• and
• a switch circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said switch circuit includes a plurality of switches selectively turned on or off,
• said variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more switches being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed, and
• parasitic resistance values of said plurality of switches in an ON state are so set that said variable resistance value varies approximately in steps of a predetermined value.

A variable resistance circuit that has a variable resistance value being gradually variable, comprising:

• a resistance circuit including a plurality of resistors serially connected;
• and
• a bypass circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said bypass circuit includes a plurality of transistors selectively turned on or off, said plurality of transistors are connected to ends of said plurality of resistors respectively, and
• gate widths of said plurality of transistors are so set that said variable resistance value varies approximately in steps of a predetermined value.

A variable resistance circuit that has a variable resistance value being gradually variable, comprising:

• a resistance circuit including a plurality of resistors serially connected;
• and
• a switch circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said switch circuit includes a plurality of switches selectively turned on or off, said plurality of switches are connected to ends of said plurality of resistors, and
• parasitic resistance values of said plurality of switches in an ON state are so set that said variable resistance value varies approximately in steps of a predetermined value.

A variable resistance circuit that has a variable resistance value being gradually variable based on a control signal, comprising:

• a resistance circuit including a plurality of resistors serially connected;
• and
• a bypass circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said bypass circuit includes a plurality of transistors selectively turned on or off based on said control signal,
• said variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more transistors being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed, and
• gate widths of said plurality of transistors are so set that said variable resistance value has approximately linearity with respect to said control signal.

A variable resistance circuit that has a variable resistance value being gradually variable based on a control signal, comprising:

• a resistance circuit including a plurality of resistors serially connected;
• and
• a switch circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said switch circuit includes a plurality of transistors selectively turned on or off based on said control signal,
• said variable resistance value is determined by a combined resistance value of a parasitic resistance of one or more transistors being turned on and one or more resistors being bypassed as well as a combined resistance value of one or more resistors being not bypassed, and
• parasitic resistance values of said plurality of switches in an ON state are so set that said variable resistance value has approximately linearity with respect to said control signal.

A variable resistance circuit that has a variable resistance value being gradually variable based on a control signal, comprising:

• a resistance circuit including a plurality of resistors serially connected;
• and
• a bypass circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said bypass circuit includes a plurality of transistors selectively turned on or off based on a control signal, said plurality of transistors are connected to ends of said plurality of resistors respectively, and
• gate widths of said plurality of transistors are so set that said variable resistance value has approximately linearity with respect to said control signal.

A variable resistance circuit that has a variable resistance value being gradually variable based on a control signal, comprising:

• a resistance circuit including a plurality of resistors serially connected;
• and
• a switch circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said switch circuit includes a plurality of switches selectively turned on or off based on a control signal, said plurality of switches are connected to ends of said plurality of resistors respectively, and
• predetermined resistance values of said plurality of switches in an ON state are so set that said variable resistance value has approximately linearity with respect to said control signal.

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:
• a resistance circuit including a plurality of resistors serially connected;
• and
• a bypass circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said bypass circuit includes a plurality of transistors selectively turned on or off, said plurality of transistors are connected to ends of said plurality of resistors respectively, and
• gate widths of said plurality of transistors are so set that said variable resistance value varies approximately in steps of a predetermined value.

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:
• a resistance circuit including a plurality of resistors serially connected;
• and
• a switch circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said switch circuit includes a plurality of switches selectively turned on or off, said plurality of switches are connected to ends of said plurality of resistors, and
• parasitic resistance values of said plurality of switches in an ON state are so set that said variable resistance value varies approximately in steps of a predetermined value.

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:
• a resistance circuit including a plurality of resistors serially connected;
• and
• a bypass circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said bypass circuit includes a plurality of transistors selectively turned on or off, said plurality of transistors are connected to ends of said plurality of resistors respectively, and
• gate widths of said plurality of transistors are so set that said variable resistance value varies approximately in steps of a predetermined value.

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:
• a resistance circuit including a plurality of resistors serially connected;
• and
• a switch circuit connected in parallel with said resistance circuit for bypassing one or more resistors selected from said plurality of resistors, wherein
• said switch circuit includes a plurality of switches selectively turned on or off, said plurality of switches are connected to ends of said plurality of resistors, and
• parasitic resistance values of said plurality of switches in an ON state are so set that said variable resistance value varies approximately in steps of a predetermined value.