PURPOSE: To absorb variance of capacitors and resistors subject to circuit integration and secure performance by providing plural sets of at least the resistors or the capacitors subject to circuit integration, providing a switch switching plural elements or the connection so as to control the switch with an external control signal to the integrated circuit.
CONSTITUTION: Plural integrated resistors or capacitors deciding the frequency characteristic of a filter are provided with high specific accuracy and the connection of the integrated circuit resistors or the integrated circuit capacitors is changed over by using a switch controlled from the outside of the IC. For example, a changeover switch 2 and a control signal Vs controlling the switch 2 are given in the IC1 and the changeover switch 2 is thrown respectively to positions 9, 10 depending on the H/L level of the control signal Vs. The cut-off frequency of the positive feedback secondary LPF is switched in Equations I, IIby the control signal Vs. Since the specific accuracy between resistance elements is selected high in the IC, fc1, fc2 are set to a proper value with high specific accuracy by selecting resistors R11, R12.
MIURA KUNIAKI
FUKUSHIMA ISAO
| JPS58170111A | 1983-10-06 | |||
| JPS56166616A | 1981-12-21 |
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