| 摘要 |
PURPOSE:To prevent malfunction by arranging plural resistors of a switch section, plural resistors constituting a channel selection control section and plural differential amplifiers to a constant currnt circuit in equivalent symmetry and A/D-converting a voltage D/A-converted by the switch section. CONSTITUTION:A series circuit of resistors R0-R4 constituting the switch section 21, switches SW1-SW4, resistors R10-R14 constituting a channel selection control section 20 and differential amplifiers A1-A4 are arranged to the constant current circuit 81 in the form of equivalent symmetry. An output voltage of a code pattern corresponding to the operating state of the switch section 21 is obtained by an output voltage of the differential amplifiers A1-A4 by A/D- converting the D/A-converted voltage at the switch section 21 by means of the channel selection control section 20. Thus, two leads are enough for connecting the switch section 21 and the channel selection control section 20 and this is the same even when the number of switches is increased. |
