This paper proposes two novel and compact low-power tunable AC amplifiers with ultra-low high-pass corner frequency. The circuits are based on alternative AC capacitively coupled feedback topologies using novel implementations leading to better performance in terms of area, power and noise efficiency. This is accomplished by a combination of actively boosting the resistive value of a pseudo-resistor (allowing more than two decades of tuning) and an optimization of the active devices required. Measurement results from a fabricated prototype using a 0.18<inline-formula> <tex-math notation="LaTeX">\mu</tex-math> </inline-formula>m technology are provided to demonstrate the technique. The proposed amplifiers can provide tunable high-pass corner frequencies ranging from 31 mHz<inline-formula> <tex-math notation="LaTeX">\vphantom{_{_{}}}</tex-math> </inline-formula> to 7 Hz, with power consumption as low as 0.425 <inline-formula> <tex-math notation="LaTeX">\mu</tex-math> </inline-formula>W, CMRR of 84 dB, 0.1 mm<inline-formula> <tex-math notation="LaTeX">^{2}</tex-math> </inline-formula> area, 39.7 dB gain, and integrated IRN of 2.42 <inline-formula> <tex-math notation="LaTeX">\mu</tex-math> </inline-formula>V<inline-formula> <tex-math notation="LaTeX">_{\mathrm{rms}}</tex-math> </inline-formula>.