Capacitive sensor interface and method

摘要

Electronic interface and method for reading a capacitive sensor that includes one input capacitor (30) or several input capacitors, in which the capacitive sensor is excited with a two-level voltage (Vlow, Vhigh) and read by a charge-sense amplifier whose output is sampled in four successive instants. An evaluation unit (333) is arranged to compute two difference values (V12, V34) between two pairs of samples corresponding to different voltage levels and to combine said difference values into an output value (V_out_raw) proportional to the charge transferred to the input of the charge-sense amplifier and an error value (error_bit) sensitive to a time derivative of a noise current din/dt.

主权项

1. Electronic interface for reading a capacitive sensor that includes one input capacitor or several input capacitors whose capacitance depends from a value that must be measured, the interface including at least one driver generating an electric excitation voltage that varies between a first voltage level and a second voltage level connected to one electrode of the input capacitor, and a charge-sense amplifier connected to another electrode of the input capacitor and arranged to output a signal proportional to the charge transferred to the input of the charge-sense amplifier, the interface comprising:
sampling means operationally arranged to hold four samples of the output of the charge-sense amplifier, a timing circuit triggering determining the instants of said four samples and the excitation generated by said driver such that two of said four samples correspond to said first voltage level, while the two other samples correspond to said second voltage level, and an evaluation unit arranged to compute two difference values between two pairs of samples corresponding to different voltage levels and to sum up said difference values into an output value proportional to the charge transferred to the input of the charge-sense amplifier.