Noise Figure Reduction Techniques in LNA's for Wide Band Multistandard RF Receivers

LNA's (Low Noise Amplifier) are widely used in wireless portable personal communication systems; the LNA noise directly affects the overall system performances. Here it is shown how the Noise Figure of a RF (Radio Frequency) Receiver can be reduced while satisfying the common constraints of impedance matching at the input, low power consumption and good linearity. The proposed Noise Figure reduction technique is based on the cold resistance approach and negative or positive feedback; a single BJT LNA, derived from the common base configuration, is considered. The Noise Figure reduction is obtained over a wide frequency band of operation, and is thus suitable for Multistandard applications. Different LNA feedback topologies are compared. It is shown that a Noise Figure lower than the limit of the common base configuration can be achieved, along with a current consuption of a few mA, over a wide frequency band of operation. Noise Figure calculations and circuit simulation results are presented and compared.