| 摘要 |
PURPOSE:To suppress a spike noise when changing over a resistor, by connecting a semiconductor switch to a feedback resistor of a high gain amplifier, and connecting a saw tooth signal generating circuit to its control terminal. CONSTITUTION:Between input/output A, B of a hign gain amplifier 4 is connected a parallel circuit consisting of a resistance 5, and a series circuit of a switching element 13, a resistance 9 and a switch 7, and an input current is converted to voltage and an output signal is obtained. One terminal of a saw tooth signal generating circuit 15 is connected to a control terminal of the element 13, and the other terminal of the circuit 15 is connected to a terminal S of a switch 17. The switch 17 selects output voltage P of the amplifier 4 and reference voltage Q. Output voltage VG of a generator 15 is made-maximum, and the switch 7 is turned on in a state that the element 13 has been made off. Subsequently, when voltage of the generator 15 is raised and the element 13 is turned on, since resistance of the element 13 is varied slowly due to the negative feedback, no spike noise is generated in input voltage VB of the amplifier 4. |
