Keywords: rf, rfic, lna, bias, wireless, ism, ghz, gain, noise figure, linearity, ip3, iip3, return loss, 802.11, wlan, ieee Related Parts
APPLICATION NOTE 2874
2.5GHz LNA with Gain Step for 802.11b/g and Bluetooth Applications
Nov 21, 2003
Abstract: This application note presents the design of an LNA at 2.45
GHz for WLAN applications meeting 802.11b/g needs. It presents curves
that show gain, noise figure, input and output return loss, and
linearity.
The MAX2645 is a Silicon Germanium (SiGe) Low-Noise Amplifier (LNA) that features a 25dB gain step, shutdown mode, and adjustable IP3. The LNA has been optimized to improve the sensitivity of CMOS receivers for 2.4GHz, 802.11b and 802.11g applications. The device features +18.7dB of gain, a noise figure of 1.9dB, and an Input IP3 of +0.5dB in High-Gain Mode. In Low-Gain Mode, the LNA has -7.0dB of insertion loss and an Input IP3 of +15.3dB. Supply current is a low 8.9mA in High-Gain Mode, 2.7mA in Low-Gain Mode and typically 0.1uA in Shutdown Mode. The LNA also features an externally adjustable bias control, set with a single resistor, which allows the user to meet minimum linearity requirements while minimizing current consumption. Table 1 below summarizes MAX2645 performance. The schematic for optimizing the MAX2645 for 2.45GHz is represented in Figure 1. Figures 2-6 demonstrate High-Gain, and Low-Gain performance of the LNA versus frequency. For further information, consult the MAX2645 SiGe LNA and MAX2645 EV kit datasheets.
