The system is an all-digital low power Read-Out Circuit with tunable sensitivity (6.7-46.4 mbar/LSB), designed to interface a wide range of commercial resistive pressure sensors for robotic applications. Besides encoding the applied pressure with 8 bit resolution, the ROC provides contact detection as well, monitoring small capacitance variations at low pressure (less than 100 mbar). The circuit detects both capacitance and resistance variation of the connected transducer. Two all-digital sub-systems implement the conversion of the input resistance and capacitance-to-frequency, exploiting an on-chip ring oscillator as timing reference. The active area is 428×159 μm2 and the power consumption is 27.2 μW at Vdd=1.2 V and 1 kHz read-out rate.

The system is a very small active area (221×79 μm2) capacitive Read-Out Circuit (ROC), robust to supply voltage and temperature variations, designed to be replicated in an on-chip array to implement a flexible sensing skin. The design of the circuit is tightly coupled with the design (from a material science viewpoint) of the transducer, nanostructured and carbon nanotube-based. Sensitivity of the complete transducer-ROC can be co-designed with the microelectronic circuit by operating on few digital components, operated in an analog mode. The capacitance-to-frequency conversion relies on two ring oscillators, whose frequency ratio is proportional to the capacitance under-test. The system has a resolution of 5.23 fF per LSB, consuming 1.84 μW at Vdd=1.2 V and 1 kHz read-out rate.