| 摘要 |
PURPOSE:To vary a gain finely over a wide range, by providing a gain control circuit, formed by connecting plural parallel circuits each of a resistance and a switch in series, and change over switches between the output side and input side of an operational amplifier. CONSTITUTION:When the 1st and 2nd changeover switches SW1 and SW2 are both connected to contacts A, one or some of switches S1, S2...S8 in a gain control circuit 3 formed by connecting plural parallel circuits of resistances R (2R, 4R, 8R...128R) and switches S1(S2, S3, S4...S8) in series are turned on option ally and selectively to vary a gain G stepwise while G>=1. Further, a variable resistance VR is adjusted to obtain continuous variation between respective steps. When the 1st and 2nd changeover switches SW1 and SW2 are both connected to contact B, on the other hand, the gain G is varied stepwise while 0<G<=1, and the variable resistance VR is adjusted to obtain the continuous variation between respective steps. |
