Many researchers are evaluating Ultra Wideband's (UWB's) applicability for short-range, high-speed wireless communications. Yet these systems must first overcome a challenging building block: the low-noise amplifier (LNA). A UWB LNA was recently proposed by Jihak Jung, Taeyeoul Yun, and Jaehoon Choi from Hanyang University in Seoul, Korea in conjunction with Hoontae Kim from the Samsung Advanced Institute of Technology. This CMOS LNA has a common-source feedback topology and wideband matching techniques. It simultaneously satisfies the requirements of multiband OFDM UWB systems in both noise and bandwidth.
The LNA is composed of two stages. The first stage optimizes the low-noise performance while the second one improves the amplifier's linearity. The second stage also uses a shunt-peaking load to extend the 3-dB band at high frequencies. Interestingly, this topology boasts noiseless input matching. The LNA employs the optimum values of feedback resistors Rf (500 to 800 W) to produce wideband input impedance matching without significantly impacting the noise figure. The resistive and capacitive shunt feedbacks also improve stability, gain flatness, and bandwidth.
Measurement results showed maximum gain of 13.5 dB within a 3-dB bandwidth from 1.85 to 10.2 GHz and return loss of less than 10 dB from 3 to 11 GHz. The fabricated LNA achieves an average noise figure of 4.5 dB from 1.85 to 10.2 GHz. The input-referred third-order intercept point and 1-dB compression point are obtained as -1 dBm and -9 dBm, respectively, while consuming 13 mW in a 0.19-µm CMOS process. See "Wideband and Low Noise CMOS Amplifier for UWB Receivers," Microwave And Optical Technology Letters, April 2007, p. 749.