Summary We present the design of a low‐power high open‐loop gain opamp for use in chopper‐stabilized capacitively coupled instrumentation amplifiers (CCIAs). The opamp utilizes the current‐reuse folded‐cascode topology and a low‐power gain‐boosting technique to maximize its power efficiency and open‐loop gain. The proposed technique is applied to the designs of two CCIAs: the conservative CCIA with a moderate current scaling ratio and the stringent CCIA with a very high current scaling ratio. Utilizing the current scaling ratio of 4:1, the conservative CCIA, designed and fabricated in a 0.18 μm CMOS process, consumes a total current of 1.69 μA from a 0.8‐V supply voltage and achieves a thermal noise floor of 56.5 nV/ Hz. Utilizing the current scaling ratio of 38:1, the stringent CCIA, designed and simulated in a 0.13 μm CMOS process, consumes a total current of 1.4 μA and achieves a thermal noise floor of 48 nV/ Hz. The proposed design technique should benefit the designs of low‐power instrumentation amplifiers in advanced processes in which channel‐length modulation and the limited current consumption and supply voltage make the designs of high open‐loop gain opamps difficult. Copyright © 2017 John Wiley & Sons, Ltd.

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