A 0.1–3.2 GHz Reconfigurable LPF With Peaking Reducing and Selectivity Enhancement Using Adaptive Impedance Transformation

This paper presents an on-chip low-pass filter (LPF) for cognitive radio in a 130-nm SiGe BiCMOS technology. The LPF achieves a tuning range of 0.1-3.2 GHz with a 100 MHz step. To address gain variation caused by the frequency peaking effect, we propose an adaptive impedance transformation (AIT) technique, achieving a remarkable ripple of less than 3.01 dB across the entire 0.1-3.2 GHz frequency band. This technique also enhances passband selectivity. Furthermore, we introduce a novel OPAMP featuring a four-stage HBT-CMOS composite pair. Leveraging the inherent advantages of both HBT and CMOS technologies, this OPAMP elevates the GBW from the 0.834 Grad/s of a CMOS-only topology to an impressive 8.33 Grad/s. The LPF requires only 8 mA at 1.5 V and 17.5 mA at 2 V. With its wide-tuning range, the proposed LPF achieves a state-of-the-art figure of merit (FoMT ) of 1939, underscoring its suitability for cognitive radio applications.