1.58-GHz Third-Order CMOS Active Bandpass Filter With Improved Passband Flatness

This paper presents a third-order active bandpass filter (BPF), realized in an area of 0.58% λ
₀
by 0.44% λ
₀
at 1.58 GHz (not including contact pads and λ
₀
is the free-space wavelength at 1.58 GHz) using standard 0.18-μm CMOS one-poly six-metal technology. A survey of the literature shows that a prototype of such a BPF has the lowest normalized area per resonator of active BPFs. The synthetic transmission line, which is used in the active BPF herein, enables the prototype to be substantially miniaturized. Moreover, this paper describes a modified composite cross-coupled nMOS resonator that can equalize passband ripples. A comparison between the measured and simulated data verifies the third-order filter response with 8% 3-dB bandwidth at 1.58 GHz. The insertion loss is 0.68 dB at the central frequency with a passband ripple of 1.24 dB and the active BPF consumes 8 mA from a 1.8-V supply.