Noise-Canceling LNA Delivers 4.5-To-5.1-dB Noise Figure Over UWB Band

Ultra-Wideband (UWB Technology promises to transmit data at a high data rate while keeping power low. The industry is therefore counting on it to provide seamless connectivity between consumer-electronics devices for the transmission of high-bandwidth data like video. The front-end, wideband low-noise amplifier (LNA) will be critical to such capabilities. ChihFan Liao and Shen-Iuan Liu of Taipei's National Taiwan University developed a UWB 3.1to-10.6-GHz LNA that employs a broadband noise-canceling technique.

This prototype LNA, which is fabricated in 0.18-┬Ám CMOS, achieves a power gain of 9.7 dB over a 3-dB bandwidth of 1.2 to 11.9 GHz. Its noise figure is 4.5 to 5.1 dB over the entire UWB band. The integrated-circuit (IC) consumes 20 mW from a 1.8-V supply.

If this circuit and design methodology is used, the noise from the matching device should be greatly suppressed over the desired UWB band. This approach also promises to minimize the noise from other devices performing noise cancellation. Of course, the purpose of noise cancellation is to decouple the input matching with the noise figure. To achieve this goal, it cancels the output noise from the matching device.

In the proposed LNA, a 4-pF bypass capacitor provides an AC ground over the full band. By using two inductors for shunt peaking, the bandwidth is extended. In addition, the on-chip inductors' practical Q limits the peaking to less than 1 dB. By reducing the number of high-Q inductors in a filter-based topology, the LNA occupies just 0.59 mm2. See "A Broadband Noise-Canceling CMOS LNA for 3.1- 10.6-GHz UWB Receivers," IEEE Journal of Solid-State Circuits, February 2007, p. 329.

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