A self-tuning technique for optimization of dual band LNA

This paper presents a self-tuning technique for optimization of a dual band LNA that can be used in a flexible RF front-end suitable for IEEE 802.11a/b/g WLAN applications. With this tuning technique the LNA can perform self-calibration for the optimal performance. A possible shift in resonance frequency due to process and temperature variations can be compensated by this method. The proposed self-tuning technique is implemented by using a simple RF detector at the LNA output. Based on the DC value provided by this detector the LNA is tuned for a maximum gain through the tuning loop, which incorporates ADC, digital base-band and DAC. We show that the tuning error can be within half LSB of ADC provided the DAC and ADC resolutions are constraint by a specified condition. For 4-bit case this value corresponds to a gain error of 0.4 dB. The LNA has been implemented in 0.2 mum GaAs process offered by OMMICtrade. In measurements the LNA achieves a gain of 15.1 dB and 21.6 dB in the upper and lower band, respectively, with corresponding NF of 3.8 dB and 2.8 dB. In the lower band the measured IIP3 is -3 dBm and 1 dB_CP is -8 dBm.