A Low-Cost CMOS Reconfigurable Receiver for WiMAX Applications

This paper presents a low cost solution for lower frequency WiMAX CPE receivers. A receiver which consists of wideband LNA, switching mixer, VCO and reconfigurable low-pass filter have been designed and simulated in different WiMAX receive bands such as in the 2.3-GHz band, in the ISM band (2.4-GHz), and in the 2.5-GHz band, as well as in different channel bandwidths, ranging from 1.75 MHz up to 10 MHz. The zero-IF architecture is chosen as it suits for receivers using OFDM signals with null DC subcarrier. The LNA and switching mixer have been fabricated in 0.18 mum RF- CMOS technology and the measurement results show that these building blocks have a combined RF-to-IF gain of 20-dB, a DSB noise figure of 3.5-dB, an RF-to-IF IIP₂ and IIP₃ higher than +20-dBm and 0-dBm, respectively. The circuit consumes 16-mA from 1.8-V supply and occupies a die area of 0.42 times 0.50 mm². Simulation results of the negative-Gm VCO show that it can oscillate at the desired frequencies with phase-noise performance of better than - 125-dBc/Hz at a frequency offset of 3.5 MHz. A reconfigurable 4^th order of Gm-C low-pass filter (LPF) has been designed using two 2^nd order biquad g_m- C LPFs and its simulation results show that - 3-dB frequency corners can be adjusted to 1.75-MHz, 3.5-MHz, 7-MHz and 14-MHz. Both VCO and LPF are simulated using 0.18 mum RF-CMOS technology.