HIGH-RELIABILITY DESIGN METHOD OF LC TUNING CIRCUIT AND SUBSTANTIATION OF AGING CHARACTERISTICS FOR 20 YEARS

In 1963, the authors began to develop a tuning circuit (hereafter refe rred to as the 'circuit') consisting of an inductor, fixed capacitors and a variable capacitor. The circuit required very high accuracy and stability, and the aging influence on resonant frequency needed to be Delta f/fo greater than or equal to+/-0.12% for 20 years. When we star ted, there was no methodology available for designing such a long-term stable circuit, so we reinvestigated our previous studies concerning aging characteristics and formed a design concept. We designed the cir cuit by bearing in mind that an inductor was subject to natural and st ress demagnetization (as indicated by disaccommodation), and assumed t hat a capacitor changed its characteristics linearly over a logarithmi c scale of time. (This assumption was based on short-term test results derived from previous studies.) We measured the aging charac teristic s of the circuits at room temperature for 20 years, from 1966. The mea surement results from the 20-year study revealed that the aging charac teristics predicted by the design concept were reasonably accurate.