1. An apparatus comprising: a first operational transconductance amplifier to determine a voltage drop of a first impedance; a second operational transconductance amplifier to determine a voltage drop of a second impedance and wherein an output node of the second operational transconductance amplifier is coupled to an output node of the first operational transconductance amplifier; and at least one current source to adjust the voltage drop of the first impedance and the voltage drop of the second impedance and to provide a compensating current based on a difference between the voltage drop of the first impedance and the voltage drop of the second impedance.