| 摘要 |
PROBLEM TO BE SOLVED: To automatically adjust the filter and to facilitate the frequency adjustment of the filter by making variable resistance which determines the frequencies of an oscillation circuit and the filter constituted on the same integrated circuit element, and adjusting the oscillation frequency through interlocking control. SOLUTION: When capacitors C3 and C4 of a multivibrator oscillation circuit MV of an FM radio receiver, etc., reaches 80% of a standard value, capacitors C1 and C2 of the filter circuit FL of the same semiconductor integrated circuit vary at the same ratio because of characteristics of the manufacturing process of the semiconductor integrated circuit to reach 80% of the standard value. Therefore, a control circuit CON increases the values of variable resistors RE3 and RE4, and RE1 and RE2 of both circuits MV and FL by 1.25 time at the same time to cancel variation in capacitance, so that the frequencies of both circuits are adjusted to set values. While the frequency of the oscillation circuit is monitored, the resistance values are controlled to make the adjustments to the set values, so that the frequency of the filter can also be adjusted to the set value automatically. |
