Differential floating dual slope converter

DETAILED DESCRIPTION OF THE INVENTION The invention is shown in typical embodiment in FIG.
1 and includes a pair of input terminals 10 and 12 to which a differential signal is applied from a transducer in a weighing or force measuring system, or from another suitable source.
These input terminals are coupled by way of respective electronically controlled switches 14 and 16 to an input of a preamplifier 18.
The output of preamplifier 18 is applied via a switch 20 and capacitor C1 and resistor R1 to the positive input of buffer amplifier 22.
The buffer amplifier 22 is part of a high input impedance dual slope converter 24 which also includes integrator operational amplifier 26 and comparator 28 connected as shown with integrator input resistor R2 coupling the output of buffer 22 to the negative input of integrator operational amplifier 26 and integrator capacitor C2 coupling the output and the negative input of integrator operational amplifier 26.
The output of comparator 28 is coupled via a resistor R3 and switch 30 to the positive input of buffer 22.
The input terminal 12 is also coupled to a low input buffer amplifier 32, the output of which is coupled to the positive input of integrator 26 and the negative input of comparator 28 and which amplifier provides a reference signal to converter 24.
A resistor R4 interconnects the output and the negative input of amplifier 18 and serves as a gain control therefor.
The negative input of amplifier 18 is also coupled via a resistor R5 to the output of low input buffer 32.
A reference voltage is derived from an appropriate source by a center tapped resistor network 11 including resistors R6, R7, R8 and R9 connected as shown in FIG.
1 to respective switches 34, 36 and 38 all commonly coupled via a capacitor C3 to the junction between capacitor C1 and resistor R1.
The junction of resistors R8 and R9 is coupled via a switch 40, and the junction of resistors R7 and R9 is coupled via a switch 42, to the positive input of an offset buffer 44.
The output of buffer 44 is coupled by a resistor R10 to the negative input of preamplifier 18