Understanding Smart Sensors - Nomads.usp

262 Understanding Smart Sensors100-mm-diameter membrane provided approximately a 0.017-pF capacitancewithout applied pressure. Using up to 81 individual pressure sensors, whichwere switched in parallel, capacitance values between 1 and 2 pF were achieved.The sensor output varied approximately 0.2 pF over a 1- to 6-bar pressurerange.A multichannel probe designed for measuring single-unit activity inneural structures is shown in Figure 11.6 [7]. Eight active recording sites areselected from 32 sites on the probe shank using a static input channel selector.A large number of recording sites are desirable for sampling the total activitywithin even a restricted tissue volume. In this design, on-chip CMOS circuitryamplifies and multiplexes the recorded signals and electronically positions therecording sites with respect to the active neurons. The neuron signals typicallyhave frequency components from about 100 Hz to 6 kHz, with an amplitudefrom 0 to 500 mV. The on-chip functions of the probe include channel selection,amplification, signal bandlimiting, multiplexing, clocking, power-onreset, and self-testing.Multiple sensing sites are common in chemical measurements. A multielementsmart gas analyzer has been developed that represents one of the mostsophisticated sensors with respect to both operation and data processing [8].The multielement sensor has a number of thin-film detectors to overcome thedrawbacks of an earlier version and to improve selectivity and specificity in analyzinggas mixtures.Output leadsRecordingsitesInterconnectingleadsSignal processingcircuitrySupporting substrateFigure 11.6 Multichannel microprobe sensor. (After: [8].)