SIGNAL CONDITIONING APPARATUS AND METHOD EXHIBITING ACCURATE INPUT IMPEDANCE AND GAIN CHARACTERISTICS OVER COMMON MODE RANGE AND OPERATIONAL ENVIRONMENTS

摘要

A signal conditioning device is disclosed that has a signal conditioning circuit that is useful in applications such as automotive applications and that can adjust the detector input signal and provide, for example, a useful output to a fuel-air mixture control system. The signal adjustment circuit uses an amplifier having an input terminal connected to the detector, a detection impedance, an NMOS and PMOS transistor, and a feedback impedance. Detectors, such as oxygen detectors, have a detector output referenced to detector ground, and an input terminal connected to a power supply and power supply ground. The signal conditioning circuit uses a switched impedance to provide an output voltage proportional to the differential voltage between the detector output voltage and the detector ground when the impedance between the signal conditioning circuit input terminals is lower than the detection impedance. If not, the signal conditioning circuit using switched impedance provides an output voltage proportional to the power supply voltage. The signal conditioning circuit samples the differential voltage and power supply voltage upon sensing at a frequency derived from the clock generator. The signal conditioning circuit provides an NMOS transistor coupled to the detector with a negative bias voltage derived from a single power source, thereby allowing operation if the detector ground and the power supply ground are at different potentials. In addition, the fabrication of signal conditioning circuit impedances as capacitors using linear complementary metal oxide semiconductor technology results in very accurate gain and input impedance characteristics.