| 摘要 |
PURPOSE:To obtain a small time constant applying a simple structure and a small occupied area, by a method wherein a junction capacitance is varied by changing an inverse bias voltage applied to the junction surface of a diffusion layer and an island. CONSTITUTION:A P-type semiconductor layer 22 is stacked on a P-type substrate 21. On the semiconductor layer 22, an N-type resistance island 28 is formed, and a diffusion layer 24 is formed on the island 23 by P-type base diffusion. The island 25 is connected to high potential via a contact 27. Thus an inverse bias voltage is applied to a P-N junction surface, and the diffusion layer 24 is made electrically independent of other circuits. As the junction surface of the diffusion layer 24 and the island 23 is inversely biased, a junction capacitance is parasitic on the surface. When contacts 25 and 26 are made input output terminals, a diffusion resistance acts as a low-pass filter. Then the junction capacitance is varied by changing the potential of the contact 27, so that the time constant of the filter can be changed, and a capacitor is made practically unnecessary. |
