DE2800645

An improved interface circuit for use between variable voltage analog sensors which are measuring physical parameters and a microprocessor which is processing the data relating to such parameters. The interface unit is of the type employing an analog multiplexer, an analog to digital converter, a voltage to frequency converter, a counter for converting frequency to digital data, and a bus adapter for connection to the microprocessor. The inventive improvement relates to providing the multiplexer as a differential multiplexer having two differential voltage outputs and having a sign detector connected thereto. A switching block is connected between the differential voltage outputs and the voltage to frequency converter and also to the sign detector thereby acting as a selector circuit. The selector circuit passes each voltage output signal of the multiplexer which has a constant sign to the voltage to frequency converter, wherein the counter is an up/down counter whose counting input is connected to the sign detector output.