Optimal biasing of magnetoresistance amplifiers

The magnetoresistive amplifier is usually implemented by allowing an input signal current to modulate a magnetic field which, in turn, produces a change in the resistance of an active element in the output portion of the device. Amplifiers of this type may be classified either as a conventional type, which utilizes the normal magnetoresistive effect of the active material, or as a type which employs the characteristics of a superconducting element operating in the resistive transition region. In both cases, there has been reported experimental data which indicates that the power gain for these amplifiers is a function of the biasing magnetic field (or biasing current), and that an optimal value of the bias field exists which results in a maximum value of the power gain. Analytical methods of determining these optimal values are derived and theoretical predictions based on these methods are shown to be consistent with the experimental results.