MONOLITHIC MICROWAVE INTEGRATED CIRCUIT

PROBLEM TO BE SOLVED: To make a negative feedback amplifier operate stably by decreasing its gain at higher and lower frequencies so as to suppress oscillation. SOLUTION: A series circuit consisting of feedback resistors R1, R3, R4 is connected between the gate and drain of a FET 1. A connecting point of resistors R3, R4 connects with ground via a λ/4 micro-strip line 2a. The resistance of the resistors is selected as R1=50 ohms, R3=20 ohms and R4=5 ohms. Since the λ/4 line 2a is open at a usual operation frequency band, the integrated circuit acts like a negative feedback amplifier having a feedback resistance of 75 ohms. On the other hand, the λ/4 line 2a is short-circuited in a very low frequency as well as a higher frequency such as twice the operating frequency, so that the drain of the FET 1 connects with ground via the R4 (5 ohms) and the gain at the frequency band is decreased to suppress oscillation.