Systematic Design of EMI-Resilient Negative-Feedback Amplifiers

Abstract

The information transfer capacity of negative-feedback amplifiers, and electronic circuits in general, is limited by three fundamental limitations being noise, bandwidth, and signal power. Electromagnetic Interference (EMI) is not a fundamental limitation, but it also hampers the information transfer. EMI may have such detrimental effects that malfunctioning of the electronic circuit occurs. This may result in loss of information, or worse, possibly dangerous situations. That is a reason why susceptibility to EMI is regulated by law. The ratio of the intended signal and the errors, the Signal-to-Error ratio (SER) can be regarded as a figure of merit of the signal handling performance of an amplifier for a given input signal and electromagnetic environment. EMI from out-of-band signals, i.e., signals with a frequency (much) higher than the bandwidth of the amplifier, may result in a DC shift and detection of the, in-band, low frequency envelope variations (envelope or `AM' detection) of the high frequency interference, caused by even-order nonlinearities in the active devices used. Specifically envelope detection may severely hamper the SER, since this will often be a signal in the pass band, while DC-shifts may not be in the pass band. This work focuses on reducing the errors introduced by the fundamental limitations and EMI in negative-feedback amplifiers. A systematic design approach for application specific negative-feedback amplifiers with specified SER is proposed in this work. It enables the designer to calculate noise, bandwidth, EMI, and the required bias parameters of the transistors used in application specific amplifiers in order to meet the SER requirements.