A Sub-pA Current Sensing Front-End for Transient Induced Molecular Spectroscopy

We report an 8-channel array of low-noise (30.3fA/√Hz) current sensing front-ends with on-chip sensors for label-free, restriction-free biosensing. The analog front-end (AFE) consists of a 1 ^st -order continuous-time delta-sigma (CT-ΔΣ) modulator that achieves 123fA sensitivity and 139dB cross-scale dynamic range over a 10Hz bandwidth while consuming 50μW and occupying 0.11mm ² per channel. A digital IIR filter and a tri-level pulse width modulated (PWM) current-steering DAC are used to realize the equivalent performance of a multi-bit ΔΣ in an area/power efficient manner. This platform was used to observe protein-ligand interactions in real-time.