Microwave Active Filter using Finite Gain Amplifier

This paper deals with the design of microwave analog biquadratic filters using voltage amplifiers. A prototype bandpass filter is monolithically integrated. The chip size is only 1.3 mm2 on GaAs substrate. The filter specifications are: 2Ghz central frequency and a 3dB bandwidth of 40 MHz. A comparison with the SiGe bipolar technology is represented. The circuit represents a building block suitable for use in the cascade realization of higher order filters.

INTRODUCTION

Active filters have many advantages over passive ones because of their positive gain, a very interesting size-quality ratio, as well as an adjustable frequency response. At bwer frequencies, active filters have been widely used and reported. Many researches have led to Rauch, Sallen-Key [1], Deliyannis structures, which use an operational amplifier as an active element. Unfortunately, a low cost and high quality operational amplifiers are not yet developed in microwave frequencies. Our method is the transposition of previous works realized with Sallen-Key structures at low frequencies into microwave frequencies. The aim is to replace the operational amplifier by a voltage amplifier using passive feedback.