Accurate Measurement of On/Off Time for 802.11 b/g WLAN/WiMAX LNAs

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  • Author: Ahmad H. Abdelmajid
Digital Automatic Gain Control (DAGC) is used in most WLAN receivers that are compatible with the IEEE 802.11a/b/g standard, using Orthogonal Frequency Division Multiplexing (OFDM) modulation. Most WLAN Systems have a variable gain amplifier (VGA) internal to the receiver section, but some also use an external LNA in the front end section, with some systems also requiring the LNA to have a bypass function. DAGC in WLAN systems is used to automatically control both the VGA inside the transceiver and the external LNA in order to achieve better signal-to-noise ratio and hold the average power of the signal close to the desired level. The turn on and off time of the LNA enable pin and the gain gelect pin must be fast enough to comply with the fast switching time requirement from one signal level to another, so that the DAGC function remains accurate.