Frequency characteristics of CR double-tuned amplifier circuits

• Published in: Electronics & communications in Japan. Part 2, Electronics Vol. 70; no. 2; pp. 62 - 72
• Main Authors: Kurokawa, Susumu, Kohno, Tadashi, Ieyasu, Kenzo
• Format: Journal Article
• Language: English
• Published: New York Wiley Subscription Services, Inc., A Wiley Company 1987
• ISSN: 8756-663X; 1520-6432
• DOI: 10.1002/ecjb.4420700207

In the CR single‐tuned amplifier in general, it is difficult to realize high selectivity and high amplification when a high tuning frequency is specified. We succeeded in reducing the body effect by using a high‐frequency, field‐effect transistor as the reactance transistor and grounding the CR tuned circuit which is a load to the driving circuit. When a double‐tuned amplifier is constructed by cascading such a circuit in two stages, the frequency bandwidth can be enlarged. A stable amplifier was realized with the center frequency of 455 kHz and voltage gain of approximately 80 dB. This paper analyzes the frequency characteristics of such a CR double‐tuned amplifier circuit, deriving the formula for realizing the required double‐hump characteristics. When a single‐hump characteristic is composed by aligning the double‐tuned amplifier to the same tuning frequency, the selectivity is increased by approximately 55 percent compared with the characteristics of the singletuned amplifier, together with a considerable improvement in the roll‐off characteristics. An experimental circuit was constructed. The measurement of the frequency characteristics agreed well with the result of calculation. The double‐tuned amplifier circuit can be applied to the IF amplifier of the receiver.