An improved measurement circuit includes a current transformer and an active feedback circuit operated as a negative resistance that matches the value of the winding resistance of the current transformer. An amplifier in the feedback circuit provides power to drive a secondary current through a sense resistor and the transformer winding resistance, reducing the most significant error source in a current transformer circuit by presenting a negative impedance to the current transformer. Combined with the positive resistance of the transformer's winding, the negative impedance results in a net burden of zero on the current transformer, which eliminates the need for the transformer having to provide power to drive the secondary current. This facilitates the use of smaller transformers while achieving reduced measurement errors. Thus, a single, compact measurement device may be used in a wide range of applications with high measurement performance.