| 摘要 |
PURPOSE:To obtain an adjusting circuit eliminating the effect of a residual resistance, by providing a negative feedback circuit which receives an output voltage of a slider sliding on fixed resistors and a predetermined reference voltage and prevents its output voltage from becoming below the reference voltage or over. CONSTITUTION:A front end circuit of a radio receiver or the like is provided with voltage dependant varactor diodes 1-3 for tuning. An output voltage of variable resistors 4-6 connected in parallel is applied to the diodes 1-3 via a switch 7. The resistors 4-6 consist, of e.g., a fixed resistor 15 and a slider 16 and they contain parts 18 and 19 having a residual resistance. The output of the switch 7 is given to a non-inverting input of a comparison circuit 32, and the reference voltage from a power supply 24 is applied to the inverting input via a buffer 36. The output of the circuit 32 is fed back to the inverting input of an operational amplifier 28 of a buffer 27. Thus, the output voltage due to the residual resistance caused at the remotest position of the slider of the variable resistor is suppressed to a prescribed range. |
