Neuromodulation (NM) is the alteration of nervous tissue function through targeted delivery of a stimulus, such as electrical stimulation, into the affected neurological sites in the body. We present a bidirectional NM interface that features 100 mVpp linear input range and ability to sense data concurrent with stimulation (without blanking). The system includes a flexible 8-driver-to-64-contact custom waveform stimulator able to deliver up to 5.1 mA per driver and a 64-contact sensing unit with online blind artifact rejection unit. This artifact rejection unit removes stimulation artifacts from recorded data and allows extraction of neural biomarkers. The NM interface also features an efficient, integrated power management unit that can support various power delivery options. The proposed 64-contact interface satisfies design requirements of human-grade brain implants at unprecedented level of electronic miniaturization compared to state-of-the-art.