In the former IIT Center for Space Human Robotics (CSHR) in Torino and in cooperation with the MINES group, part of the research in the design of electronic circuits has been devoted to the implementation of pressure sensors read-out circuits. This activity has been achieved, in particular, with two different approaches, using commercially available transducers (see, e.g., Flexiforce, or FSR-400), and using in-house fabricated sensors resulting from material science research outputs.
The approach used in this context regards the use of oscillators as read-out elements, in particular ring oscillators, that can be efficiently implemented in a small silicon area or alternatively used as commercial components. This oscillator-based read-out technique is very low complexity and can be effectively used to provide read-out in robotics rehabilitation (see this paper).
ALL-DIGITAL FLEXIBLE CAPACITIVE AND RESISTIVE ROC FOR COMMERCIAL TRANSDUCERS
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.
Related publication:A. Damilano, H. M. A. Hayat, A. Bonanno, D. Demarchi and M. Crepaldi, "A Flexible Low-Power 130 nm CMOS Read-Out Circuit With Tunable Sensitivity for Commercial Robotic Resistive Pressure Sensors," in IEEE Sensors Journal, vol. 15, no. 11, pp. 6650-6658, Nov. 2015.
ALL-DIGITAL CAPACITIVE ROC FOR NANOSTRUCTURED MW-CARBON NANOTUBES-BASED TRANSDUCERS
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.
Related publication:A. Damilano; P. Motto Ros; A. Sanginario; A. Chiolerio; S. Bocchini; I. Roppolo; C. F. Pirri; S. Carrara; D. Demarchi; M. Crepaldi, "A Robust Capacitive Digital Read-Out Circuit for a Scalable Tactile Skin," in IEEE Sensors Journal , vol. PP, no. 99, pp. 1-1.