Speed capabilities of ferrite cores in NDRO operation

Nondestructive readout (NDRO) of ferrite cores with switch times of 4 ns at 80-MHz repetition rates has been attained by permeability sensing of the difference signal between a core at its remanent state (low permeability) and a core at its partially switched (maximum permeability) state. Limited duration interrogate pulses exceeding core thresholds were used. A variety of coercivities, materials, and sizes were investigated. Higher permeability differences were obtained with low-coercivity cores than with high-coercivity cores. Signals of 10 mV were obtained using 21-mil cores 6.7 mils high. Although some cores yield higher difference signals, they are not well suited for memory applications because of their size and drive requirements. Variations in remanent and maximum permeability caused by reset current amplitude were observed. A method for testing and specifying a core for an NDRO application is proposed.