| 摘要 |
PROBLEM TO BE SOLVED: To provide an FET band amplifier by which high gain can be obtained. SOLUTION: The TFT band amplifier is constituted of a multi-stage amplifier 1 formed integrally on a semiconductor substrate, and a BPF 2 which is connected as an outside component with the amplifier 1. The amplifier 1 is provided with amplifiers 11-15 of five stages and a BPF 16 which is inserted in the middle of the amplifiers 11-15. Each of the amplifiers 11-15 operates as a differential amplifier using a P-channel FET as an amplifying element. The BPF 16 passes band component wider than amplification band of the whole FET band limited amplifier. By eliminating low frequency components of a signal amplified by the amplifiers 11-13 of three stages, 1/f noise can be reduced. By eliminating high frequency components, thermal noise can be reduced. As a result, each of the amplifiers 14, 15 connected with the post stage of the BPF 16 is not saturated by noise component.
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