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Low-frequency noise, i.e., 1/f noise severely limits the low-frequency performance of magnetoresistive sensors for applications as ultrasensitive magnetic sensors. The combination of a flux concentrator and chopping system has been proposed to mitigate the effect of 1/f noise and improve the field sensitivity. This paper reports a high-efficiency chopping system for magnetoresistive sensors. A simple reluctance analysis allows us to estimate the chopping efficiency and optimize the design, and finite-element simulations confirm the operation. Experimental results based on the optimized design using an anisotropic magnetoresistance sensor validate the concept. The sensitivity of the sensor with the chopper at OFF and ON positions is determined to be 0.009 and 0.067%/Oe, respectively, which yields a high sensitivity chopping efficiency, namely 72%.