Silicon-integrated 2-GHz fully-differential tunable recursive filter for MMIC three-branch channelized bandpass filter design

In this paper, a Silicon-integrated differential-type two-stage recursive active filter based on a cellular approach is presented. This circuit is independently tunable in terms of power transmission gain, center frequency and bandwidth. The chip surface is less than 1.4 mm(2). Measurements demonstrate a 1.9-2.4 GHz center-frequency tuning range with a typical gain of 15 dB and a 3-dB bandwidth of 60 MHz. Gains up to 40 dB and bandwidths as low as 20 MHz are also achievable in the 2.05-2.38 GHz band. In the next step, the design of an integrated three-branch channelized bandpass filter is addressed. To the author's knowledge, this is the first MMIC channelized filter reported to date. The proposed filter uses an active power splitter at its input. Moreover, the branches are based on an elementary tunable recursive stage derived from the topology previously described, thus making the overall filter fully reconfigurable. This second circuit, which chip size is smaller than 3 mm(2), can perform 3-dB bandwidths of approximately 90 MHz and gains up to 20 dB within a 2-2.2 GHz tuning range. Controllable high-selectivity for each rejected band is also obtained through the generation of adjustable out-of-band transmission zeros. These two chips have been implemented using Philips QUBIC4 Si BiCMOS process [1].