A　cascaded　instrumentation　amplifier　(CaIA)　with　input-biased　pseudo　resistors　(IBPR)　is　presented　for　implantable　brain　machine　interfaces　(BMI).　The　gain　distribution　of　two-stage　cascaded　amplifiers,　instead　of　a　single-stage　amplifier,　helps　to　achieve　an　input　impedance　of　4.43TΩ　at　100Hz,　and　maintain　the　small　active　area　(0.0128　mm2).　The　input-biased　pseudo　resistors　contribute　to　a　much　lower　high-pass　corner　(fHP=0.00011Hz)　compared　with　the　conventional　structure,　the　input-referred　noise　is　only　3.836μVrms　integrated　from　0.5Hz　to　10kHz　with　0.98μW　power　consumption.Clinical　Relevance　-　This　establishes　an　area-efficient　amplifier　design　with　ultra-high　input　impedance　(4.43TΩ　at　100Hz)　and　hyper-low　high-pass　corner　frequency　(fHP=0.00011Hz),　which　is　suitable　for　long-term　monitoring　of　neural　activities　(including　slow　oscillations)　in　implantable　brain-machine　interfaces.　©　2023　IEEE.