Integrated Monolithic Crystal Filter for Citizen Band Transceivers

Abstract

This paper will describe a SSB 10.7 MHz IF filter for CB band transceivers employing an integrated capacitor circuit and four dual mode Monolithic Crystal Filters (MCFs) of AT cut Quartz. With a narrow bandwidth of 2 × 10⁻⁴, an insertion loss of less than 5 dB, and a low temperature coefficient of the center frequency of within ± 20 ppm over the range of − 35 to + 65℃, this filter also meets mechanical shock-resistance requirements. The integrated capacitor circuit consists of thin film Ta₂O₅ capacitors and interdigital gap capacitors formed on both sides of a Fine Grain Alumina (FGA) substrate. Four MCFs are directly soldered to the substrate of the integrated capacitor circuit, allowing this filter to be made smaller and lighter and have better resistance to mechanical shock. Also important, the manufacturing process is suitable for mass production.