Low-noise ampLifiers (Lnas) must achieve very low noise figures, good input and output return loss, high linearity, low current, wideband stability, and robust performance to meet the needs of modern infrastructure receiver applications. Examples of such applications include cellular/ third generation (3G), industrial scientific medical (ISM), and WiMAX/fourth generation (4G). To deliver such optimized performance with minimum tradeoffs, Skyworks recommends the use of unique design techniques and a pHEMT process technology in "Ultra-Low Noise Figure, High Gain Amplifier With High Linearity." This 10-page white paper details the different tradeoffs, design options, and implementation of a sub-1-dB, two-stage LNA with a low noise figure (~0.6 dB) to 2.5 GHz, gain above 20 dB, and linearity of more than +34 dBm.
The company found that a two-stage LNA topology with cascaded common-source amplifying stages offered the most flexibility for this design. To improve the third-order intercept point, different impedance terminations were presented to the device. A total device periphery of 300 m was chosen for the first stage of the design in order to provide broadband gain performance with low-current operation. In addition, multiple stability design techniques were used. Technical details, tradeoffs, simulation, and test-board layout and grounding are all covered in this paper to illustrate how an optimized design with pHEMT technology can meet new-product requirements without raising cost or increasing size.
Skyworks Solutions, Inc., 20 Sylvan Rd., Woburn, MA 01801; (781) 376-3000, Internet: www.skyworksinc.com.