A unidirectional amplifier with Esaki diodes

Two Esaki diodes can furnish unidirectional amplification when used in conjunction with a Hall-effect isolator. The input and output impedances of this amplifier are greater than the absolute value of the negative resistance of the diodes by a factor which is proportional to the voltage gain. The voltage gain-bandwidth product of such an amplifier is
g_{T}/4\piRC
, where g
T
is determined by the isolator and RC is the usual RC time constant of the Esaki diodes. Typically, g
T
is between 0.1 and 1. If one of the diodes is removed, the remaining network still amplifies unilaterally, but the impedance at the diode-less end drops to that of the isolator alone. In addition, a Hall-effect gyrator or circulator can be made essentially lossless by the addition of Esaki diodes.