JPS5560325A - Switched capacitor filter - Google Patents

Abstract

PURPOSE:To realize general IC-implementation by previously forming capacity constituting a switched capacitor as capacity groups with various capacity values and then by selecting fixed capacity from the above-mentioned capacity groups in accordance with characteristics of a desired filter. CONSTITUTION:In N<->-type semiconductor substrate 51, N<+>-type region 53 as a conductive layer is formed through P<->-type region 52 as an insulating layer. The surface of substrate 51 is coated with SiO2 film 54. Switched capacitors CA1-CA5 are all formed on a common model a group of capacitors differing in capacity value, e.g. capacitors 61-68 form an uniform capacitor array. Respective capacitors 61-68 has capacity values (pF) of 0.1, 0.2, 0.4, 0.8...12.8. Mark 70 is the break part of terminal wiring 71 and when a capacity value which switched capacitor CA6 should have is 3.5pF, a total capacity value of 3.5pF can be obtained at break part 70. In general, a group of capacitors consists of the (n)-number capacitors of QX2<j> denoting a minimum value by QpF, a maximum capacity of QX(2<n>-1)pF can be obtained.