| 摘要 |
PURPOSE:To provide a filter in a substrate particularly without using an external mounted element, by making the cut-off frequency of a transistor which constitutes a filter circuit in one Si substrate lower than the cut-off frequency of the transistor which constitutes other circuit. CONSTITUTION:An N type epitaxial layer 2 on a P type Si substrate 1 having an N<+> buried layer 4 is isolated by P layers 3 and 5, a P layer 6 is provided on an island 2B, a new SiO2 film 8 is opened, and thus a P layer 9 is formed shallower than the layer 6 on an island 2A. The donor is diffused simultaneously over the entire surface resulting in the simultaneous formation of a transistor Q1 at a P base 9, an N<+> emitter 10 and a P<+> collector lead-out part 11 and a transistor Q2 at the P base 9, an N<+> emitter 12 and an N<+> collector lead-out part 13. Succeedingly, a window is opened on an SiO2 film 8, and an electrode 15 is laid. Since the junction of a Q2 base layer for low-pass is deep, and the depths of Q1 and Q2 emitter junctions are the same, the Q2 base width is wide resulting in the decrease of the shield frequency fT. When Q1 and Q2 are connected to a wave detector, a filter circuit is formed. When a Darlington circuit is constituted by combining the Q1 for a general circuit and the element of the same constitution, the decrease of hFE of the Q2 can be compensated. |
