Smart Sensor Systems

11

Data Acquisition for Frequency- and Time-domain Sensors

Sergey Y. Yurish

11.1 Introduction

The rapid development of microsystems and microelectronics promotes the further development of different time-domain sensors and transducers due to advantages of frequency (period) and duty-cycle as informative parameters of sensors output signals: high noise immunity and output signal power; wide dynamic range; high accuracy of frequency standards (references); simplicity of communication, interfacing, integration and coding.

Frequency–time domain sensors are rather interesting from a technological and fabrication compatibility point of view, because of their metrology performances and the simplifications of the signal conditioning circuitry and measurand-to-digital converter. The simplicity yields a reduction of the required hardware and/or of the chip area. Such sensors are based on resonant phenomena and variable oscillators, whose information is embedded not in the amplitude but in the frequency or the time parameter of the output signal. The output signals are modulated in one of the domains of frequency (f_x), period (T_x = 1/f_x), pulse width (t_p), spacing interval (t_s), duty cycle (t_p/T_x), on-line time ratio or the off-duty factor (T_x/t_p), pulse number (N), phase shift (φ_x) or the single time interval (τ) output. Because the relevant information is simultaneously in both the analog and digital domain, these sensors have been called ‘quasi-digital’. A definition of such sensors is ...