Abstract:
The design parameters were thoroughly investigated for a low-noise transistor switch capable of meeting EMI specification requirements when switching direct current. The principles used in the design of the switch were to suppress the current leading to the transistor base and to select a transistor such that the resultant amplitude spectrum of the current was within the required current probe limits. The investigation included the evaluation of transistor parameters for low-noise switching, the proper selection of filter components, and the proper placement of the components. The values for the filter components were based on the transistor gain from which the maximum tolerable amplitude spectrum of the driving voltage waveform was determined. The design parameters were matched against derived general equations which are well tabulated for general utility and are obtained by use of modern network theory where the current waveform and subsequent amplitude spectrum are derived by Laplace-Fourier transform methods.