| 摘要 |
PURPOSE:To increase input dielectric strength, to improve a distortion factor, and to eliminate the influence of an external noise by providing a variable resistance element, an exponential circuit(EXP circuit) which determines the variation curve of the variable resistance element by a control voltage, and a photo-electric circuit which connects the variable resistance element and EXP circuit mutually on the same wafer element. CONSTITUTION:A buffer circuit 9 is provided on one silicon wafer element 8 of a variable resistance circuit, the EXP, circuit 10 is connected to its output, and a switch circuit 11 is connected to the output of the EXP circuit 10. Further, the photoelectric circuit 12 is connected to the output of the switch circuit 11 and the variable resistance element 13 is connected to the output of the photoelectric circuit 12. In this constitution, the circuit 9 connects a control voltage from a control terminal 14 to a next-stage circuit 10 with high impedance. The circuit 10 applies a control voltage which has a logarithmic curve to the resistance element 13 through the circuits 11 and 12 when an external input voltage is linear.
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