Patent ID: 6693486
Filing Date: 2004-02-17
Classification: G01F

Abstract:
A signal processing circuit for a differential voltage as the signal to be processed, especially for a magnetoinductive flowmeter, said circuit comprising at least one differentially-operating preamplifier having an input side and an input impedance, said differentially-operating preamplifier being provided on said input side with two input-coupling capacitors, two operation amplifiers each having inputs, and a resistance network connected between said inputs of the operational amplifiers and said input-coupling capacitors, said resistance network comprising two bootstrapped main resistances R1 and R1â€² connected to the input-coupling capacitors, two auxiliary resistances R2 and R2â€² connected in line with each other and together connecting the two boot-strapped main resistances R1 and R1â€² with each other, two auxiliary resistances R3 and R3â€², the auxiliary resistance R3 connect the boot-strapped main resistance R1 and the auxiliary resistance R2 with an input of one of the operational amplifiers, and the auxiliary resistance R3â€² connecting the boot-strapped main resistance R1â€² and the auxiliary resistance R2â€² with an input of the other operational amplifier, an auxiliary resistance R4 connected between the auxiliary resistances R2 and R2â€² and mass potential, whereby time constants for differential signals are smaller than time constants for common-mode signals and said input impedance of the differentially-operating preamplifier is higher for common-mode signals than for differential signals.