Stabilized threshold circuit for connection to sensing transducers and operation under varying voltage conditions

Claim 1

Stabilized threshold circuit to obtain a derived output signal from a gas composition sensing transducer (18) comprising a reference voltage generator circuit (l5, 22) connected across the supply circuit (l3, 21) and having stabilized reference output terminals (13, 14); a voltage divider circuit (11, 12) connected to the stabilized output terminals (13, 14) and thus to the reference voltage (Uref) generated by said reference voltage generating circuit; an operational amplifier (10) connected as a threshold switch; an emitter follower transistor (16) having one terminal of the transducer (18) connected to the base thereof, one current supply terminal of the emitter follower transistor being connected to one terminal (13) of the supply circuit and the other current supply terminal being in circuit connection with said stabilized output terminal (14), the operational amplifier having one input connected to the tap point of the voltage divider circuit (11, 12) and the other input to the output of the emitter-follower connected transistor, the other terminal of the transducer (18) being connected to a stabilized output terminal (13) of the supply circuit; and a compensation semiconductor element (20) having a semiconductor junction, one terminal of said junction being connected to the reference voltage, a balancing resistor (19) connected in series with said junction with one terminal thereof, and to the main current path of the emitter follower transistor (16) with the other terminal thereof, to provide a stabilized voltage thereto, the junction characteristics of the compensation semiconductor element being similar to the junction characteristics of the semiconductor junctions of the emitter-follower transistor (16).