Miniature high-frequency magnetic amplifiers for magnetic memory sensing

Amplifiers of the magnetic modulator type have been found useful for amplifying signals as small as 10-13 to 10-17 watts.1,2 The most common design utilizes balanced cores and a flux coupled output circuit separate from the excitation circuit. The output is the difference output of the cores and is predominantly second harmonic in content. The zero drift is small because core unbalance results only in generation of a fundamental output component which can be supressed by filtering,3 and the elimination of “series-connected” loads in the excitation circuit reduces drifts arising from excitation amplitude fluctuations 4 Parallel connection of windings which introduces problems of d-c resistance balancing, and the use of output rectifiers which results in drifts arising from d-c feedback, are also avoided to reduce zero drift further.