Abstract: A differential load amplifier for receiving two measurement currents from a differential piezoelectric sensor and outputting a voltage proportional to a useful signal measured by the sensor. The differential load amplifier includes a subtraction device for determining a difference signal between the two measurement currents received from the sensor, and an integration device including and an integration capacitor for integrating the difference signal determined by the subtraction device. The subtraction device includes a negative immitance impedance converter, and the integration device includes an operational amplifier connected as an integrator. The subtraction and integration devices may also be implemented by a differential current amplifier and an integration capacitor, respectively.

Abstract: A digital frequency demodulator includes a first counter and a second counter measuring the instantaneous and mean values of the period of a frequency modulated signal. A comparator compares the values measured and creates a binary signal of the same frequency as the modulation signal. The measurement of the instantaneous value of the frequency modulated signal is effected by counting the number of reference clock pulses during a period of the modulated signal, and the measurement of the mean value is effected by counting the number of pulses of a clock signal of frequency N times lower than the reference clock during N periods of the modulated signal.