Very Small MMIC Variable Frequency and Q Factor Active Bandpass Filters Using Novel Positive and Negative Feedback Design Techniques

Hideo SUWAKI  Takashi OHIRA  

IEICE TRANSACTIONS on Electronics   Vol.E76-C   No.6   pp.919-924
Publication Date: 1993/06/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Microwave and Millimeter-Wave Technology for Advanced Functions and Size-Reductions)
MMIC,  filter,  feedback,  Q-factor,  unity coupler,  

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This paper presents newly developed very small MMIC bandpass filters along with novel positive and negative feedback techniques. In order to maintain the expected Q factor without unwanted oscillations in the positive feedback loop, the unity-coupler principle is proposed to stabilize the constituent amplifier. A prototype bandpass filter is monolithically integrated in a very small area of only 0.1 mm2 on a GaAs substrate. A sharp factor as high as 5.6/1-30 dB is achieved near the frequency range of 1 GHz. The other technique presented in this paper is to achieve the bandpass function without using any positive feedback. This is negative feedback consisting of feedback elements with the unique variable transfer function of b/(1as). A variable bandpass filter based on this design concept is also fabricated in a 1.21.3 mm2 area on a GaAs substrate. It has both a varactor and varistor integrated in the circuit, resulting in an independently controllable center frequency and Q factor. It is shown experimentally that the Q factor is controllable over a remarkable range of 20 to 400 and the center frequency is broader than 100 MHz at the 1 GHz band. By cascading two of the fabricated MMIC chips, a forth-order frequency response is successfully obtained along with a 35-40 dB forward gain and an in-band gain flatness of 0.35 dB.