2.4-GHz Tunable Miniature CMOS Active Bandpass Filter with Two Transmission Zeros Using Lumped Stepped-Impedance Ring Resonator

This paper demonstrates a small-size 2.4-GHz CMOS active bandpass filter with two transmission zeros using a lumped stepped-impedance ring resonator. To obtain low insertion loss and small size, four high-Q active inductors using 0.18µm CMOS transistors only are employed in the design. The measured insertion loss is 2.9-dB at 2.4 GHz center frequency with two transmission zeros located at 2.1 GHz and 3.1 GHz, respectively. By tuning the bias currents of active inductors, the center frequency has 1.4 GHz tuning range and the 1-dB bandwidth can be adjusted in the range of 190 MHz to 260 MHz. The demonstrated active filter occupies a small chip area of 0.47 mm × 0.33 mm excluding I/O pads and has 24 dB noise figure. Thus, an active filter with a preceding two-stage common-source LNA for suppression of noise of the active filter is also demonstrated and the resulting LNA + active filter has 6 dB noise figure. The power consumption of the active filter core and the LNA core is 9 mW and 7.2 mW, respectively.