A High Linearity Darlington Intermediate Frequency (IF) Amplifier for Wide Bandwidth Applications

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  • Author: Haki Cebi
If amplifiers are used in many applications, including base stations, cable TV and instrumentation. High linearity is one of the most desired features of an IF amplifier. New applications, such as amplifiers used in cable TV, also require very flat gain and low noise. Darlington amplifiers with single or dual RF feedback topologies have been shown to have higher gain, flatness and linearity over a wide bandwidth.1,2 Various device process technologies, including HBT, SiGe and PHEMT among others, have been used in the past. Each technology has its unique advantages. Different active, dynamic and passive biasing techniques have also been used to improve performance over temperature and over the frequency band of operation.3,4 Capacitive peaking techniques are used to further increase the bandwidth, with a trade off in input and output return loss.5 The drawback in most high linearity designs is the big trade off in noise figure (NF).