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This work presents a micro-power low-offset CMOS instrumentation amplifier integrated circuit with a large operating range for biomedical system applications. The equivalent input offset voltage is improved using a new circuit technique of offset cancellation that involves a two-phase clocking scheme with a frequency of 20 kHz. Channel charge injection is cancelled by the symmetrical circuit topology. With the wide-swing cascode bias circuit design, this amplifier realizes a very high power-supply rejection ratio (PSRR), and can be operated at single supply voltage in the range between 2.5-7.5 V. It was fabricated using 0.5-μm double-poly double-metal n-well CMOS technology, and occupies a die area of 0.2 mm2. This amplifier achieves a 160-μV typical input offset voltage, 0.05% gain linearity, greater than 102-dB PSRR, an input-referred rms noise voltage of 45 μV, and a current consumption of 61 μA at a low supply voltage of 2.5 V. Experimental results indicate that the proposed amplifier can process the input electrocardiogram signal of a patient monitoring system and other portable biomedical devices.