An integrated CMOS interface for lambda sensor

Automotive pollution can be reduced by suitably controlling the mixture that is fed to the cylinders. This can be performed by means of a feedback loop including a lambda sond and a processing unit which controls the electronic fuel injectors. This paper describes a CMOS interface which adapts the output signal of a lambda sensor to allow its feeding into the processing unit. It provides a differential to a single-ended conversion with a good common mode rejection, a level shifting around a given reference voltage, and an accurate voltage gain. Both design considerations and the measurements performed on an integrated test structure are presented. The measured variation of the large-signal voltage gain for an input signal of 0 to 1 V is within ±5% when the input common mode voltage ranges from -1 V to 1 V with respect to the negative supply voltage. An output voltage with a precision within ±1 mV is obtained in the presence of an input voltage corresponding to the stochiometric composition of the mixture