Flexible Linearity Profile Low Noise Feedforward Amplifiers for Improving Channel Capacity

This paper describes a highly linear Low Noise Amplifier (LNA) exhibiting a flexible linearity profile intended as a way to meet future flexible mobile communications standards. This has the potential of inclusion in Ad-hoc Software Defined Radio (SDR) networks where a frequency hand and modulation scheme can be chosen based on the characteristics of the frequency spectrum and user requirements. The linearity profile of the LNA is tailored to cancel distortion generated as a function of the received power profile. This improves the receiver’s tolerance to unwanted signals present in the frequency hand of interest and reduces the requirement of coding and equalisation tu compensate for receiver limitations whilst increasing the available capacity. The flexible linearity profie is achieved hy the use of a feedforward amplifier structure which has the capability of large distortion suppression determined by the gain and phase balances within its two loops. To ensure maximum distortion cancellation in the band, adaptive cancellation is used to maximise the cancellation of harmful distortion.