A first grounded-emitter amplifier transistor is followed in direct coupled cascade by a second grounded-emitter amplifier transistor. The first grounded-emitter transistor has directcoupled collector-to-base negative feedback to regulate its collector current to be proportional to applied input current. The direct-coupled feedback includes means to regulate the collector-to-base potential of said first transistor to be proportional to the logarithm of the applied input current. The collector current of the second transistor is thereby in fixed proportion to the applied input current and independent of the forward current gain of the transistors.