Method and circuit for the conversion of variable physical quantities occurring in vehicles represented as frequencies into numerical values or signals proportional to the frequencies

A circuit for converting a variable physical quantity occurring in a vehicle represented by frequency variations being temporarily disturbed at times into a numerical signal proportional to said variations for further processing comprising:

• a comparator including
• a subtractor having a negative input and a positive input, said positive input receiving a pulse train whose frequency varies proportional to said physical quantity,
• a first integrator coupled to the output of said subtractor, and
• a dead-zone detector coupled to the output of said first integrator, said dead-zone detector providing a first distinct output signal when the output signal of said first integrator is below a predetermined first lower threshold level, a second distinct output signal when the output signal of said first integrator is above a predetermined first upper threshold level, and a third distinct output signal of said first integrator is between said first lower and said first upper threshold levels;
• a filtering means of the n-th order coupled to the output of said dead-zone detector having an output coupled to said negative input, where n is an integer greater than zero, said filtering means including at least one section having a variable transfer characteristic;
• and
• a detector and control circuit coupled to said dead-zone detector and said one section to detect a signal representative of a time derivative of a value proportional to said physical quantity and to provide a control signal for said one section to vary said transfer characteristic if said time derivative signal departs from an area bounded by a predetermined second lower threshold level and a predetermined second upper threshold level, said first lower and said first upper threshold levels lying within said second lower and said second upper threshold levels.