Patent ID: 6446488
Filing Date: 2002-09-10
Classification: F02D,G01N

Abstract:
A gas concentration measuring apparatus comprising:a gas concentration sensor exposed to a gas, said gas concentration sensor being responsive to application of voltage to produce a current signal indicative of concentration of the gas; and a voltage applying circuit including an operational amplifier which operates on a source voltage developed between a first and a second source voltage developed between a first and a second source terminal thereof connected to a voltage source, the operational amplifier outputting voltage for developing the voltage applied to said gas concentration sensor which has a level changing as a function of voltage inputted to the operational amplifier, wherein an npn transistor is disposed in an output stage of the operational amplifier, the npn transistor serving as a current sink element and connecting at an emitter with ground and at a collector with an output terminal of the operational amplifier, and the operation amplifier is designed to have an amplitude of each of the voltages inputted to and outputted from the operational amplifier which falls within a given input/output voltage range defined between an upper limit and a lower limit of a source voltage range of the voltage developed by the voltage source between the first and second source terminals of the operational amplifier and the amplitude having a difference of less than or equal to 0.6 V between at least one of the upper and lower limits of the source voltage range.