| 摘要 |
PURPOSE:To reduce the variable quantity of the threshold value of an MOS transistor constructing a source follower circuit by a method wherein impurity concentration on the surface of a semiconductor substrate whereat a first MOS transistor is to be formed is made higher than impurity concentration of the surface of a semiconductor substrate whereat a second MOS transistor is to be formed. CONSTITUTION:The voltage of the source 2 of a first MOST 5 is fixed to the VSS, while at this time, when a second MOST 9 conducts, and in the source 6 of the second MOST 9, no current remains therein to flow out as output DouT, or when the remainder is extremely small, the level rises up to the level of Vcc-VTH. Accordingly the surface of the substrate of the first MOST 5 is constructed of a P<++> type layer of high impurity concentration, while the surface of the substrate of the second MOST 9 is constructed of a P+ type layer of comparatively low impurity concentration, and an increase of the threshold voltage based on the source voltage rise is suppressed. Accordingly, the variation of the threshold voltage to be generated according to the source potential rise can be reduced to enable stabilization of operation. |
