MONOLITHIC HBT TYPE ACTIVE TUNABLE BAND-PASS FILTER

摘要

PROBLEM TO BE SOLVED: To provide an active tunable band-pass filter provided with a negative resistance circuit which generates the tunable amount of a negative resistance to a passive band-pass filter structure so as to compensate a resistance loss. ;SOLUTION: A negative resistance circuit 20 is provided with a bipolar transistor Q1 having a base connected to a passive filter structure through a shunt and a collector connected to a shunt guide element 32. A negative resistance is generated at the base of the transistor Q1 and impressed upon the passive filter structure. A rough Q-factor tuning circuit 36 is coupled with the emitter of the transistor Q1 and supplies a rough tuning amount of the negative resistance. In addition, a fine tuning circuit which supplies the fine tuning of the negative resistance is connected to the emitter terminal of the transistor Q1. The fine tuning is manually or automatically attained by means of a control circuit. Rough and fine tuning functions supply a tunable resistance which removes oscillations and compensates the variation of a resistance loss for realizing an improved Q-factor.;COPYRIGHT: (C)1996,JPO